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wximpact Seattle, WA

Page history last edited by alerner2@... 12 years, 3 months ago
Weather Impacts

Seattle, Washington






                                           City of Seattle, Washington





Geographic Location 



Sitting in between the Olympic Mountains to the west and the Cascade Mountains to the east, Seattle, Washington can be found in the lowland hills on the eastern banks of the Puget Sound. Seattle’s proximity to both the Pacific Ocean and Canada has allowed it to become the largest urban metropolis north of San Francisco, CA covering an area of 83.9 mi2. [A2]


Seattle: Latitude: 47.63 N, Longitude: 122.33 W


A6, A7



The Puget Sound is the lifesource for most of the population in Washington State. Tourism, recreation, fishing and other port jobs such as importing and exporting goods, as well as water to provide for millions of people are all provided by the Puget Sound.  The Pacific waters are able to flow into the state about 50 miles to Seattle, and then part both north into Canada towards Vancouver, and south to both Tacoma and Olympia, Washington’s capital. A3



Seattle ranges from sea level to an elevation of 450 feet above sea level. Only 54 miles southeast of the city you can find Mt. Rainer. At 14,410 feet, the stratovolcano is the highest peak in the Cascade Mountains. A4



Mt. Rainer - the tallest peak in the Cascade Mountains to the east of Seattle.


  A8, A34, A37





 What effects does Mt. Rainer have on the Pacific northwest?  If and when Mount Rainer erupts, it can have devastating impacts.  Many predict the eruption will be similar to that of Mount St. Helens, producing pyroclastic flows that destroyed everything in its path for 4 miles from the summit and nearly incapacitated other wildlife for the next 9 miles, when Mt. St. Helens erupted.  Unlike Mt. St. Helens, Mt. Rainer sits much closer to many more populated areas.  Other non-volcanic events have already proven to be destructive in the past.  Most of these are lahars and avalanches falling from the very steep slopes of the volcano due to earthquakes, which happen about 30 times every year.  One debris flow went 60 miles, until it was halted by the Puget Sound! [A35] These lahars and lava flow won't only affect the land nearby the mountain, but can affect vegetation, the quality of water, and cause inestimable amount of monetary damage. [A36] The last time Rainer erupted was 2,200 years ago, but is the third most active volcano in the Cascades.



Distances from Seattle, WA A5



Olympia, WA – 29 mi

Victoria, Canada (British Columbia) – 72 mi

Vancouver, Canada (British Columbia) – 115 mi

Portland, OR – 147 mi

San Francisco, CA – 681 mi

Los Angeles, CA – 957 mi

Chicago, IL – 1,736 mi





When founded, Seattle was built upon the Seven Hills of Seattle.  Although much of the downtown area has been leveled off by human development, the city is still noticeably hilly, with an elevation range of 0-450 ft. above sea level. A15

In addition to re-grading projects that have leveled the city off, many man-made bodies of water exist within Seattle including the Duwamish Waterway and the Lake Washington Ship Canal. The latter connects Lake Washington and the Puget Sound across the city, allowing eastern Washington access to the Pacific Ocean. A total 41% of Seattle is covered by water. A10



Features that define Seattle A15, A10, A16

Puget Sound- Located to the west of Seattle it covers 1,020 square miles, has an average depth of 450 ft., and a maximum depth of 930 ft. just north of Seattle. The Sound allows Seattle access to the Pacific Ocean.

Lake Washington- Located to the east of Seattle, it is the second largest natural lake in the state of Washington. It covers 54.4 square miles, has an average depth of 108 ft., and a maximum depth of 214 ft.

Olympic Mountains- West of the Puget Sound, the Olympic Mountains can be found. The mountains are not exceptionally tall and have a maximum height of 7,962 ft.

Cascade Mountains- Located East of Lake Washington, the Cascade Mountain range spans 700 miles and has a maximum height of 14,410 ft.

Seattle is surrounded by bodies of water. A9 Mountain Ranges also surround Seattle. A11





According to the 2006 U.S. census the population of Seattle, Washington is at 562,106 residents. Gender is almost split down the middle with 49.6% of the residents being female while the other 50.4% are male. Whites make up the majority of the population at 70% followed by Asians at 13.0% followed by African Americans at 8.2% with the rest of the population being split between various other races. There is an estimated 282,414 households with 91.8% of those households being occupied. An estimated 346,584 residents over the age of 16 are employed making a median salary of $58,311 which is a little less than $10,000 more than the U.S. median. A12





Seattle has a temperate climate and is known for its rainy weather. However, the rain in Seattle is usually light or misty, unlike what we as midwesterners think of as rain. The normal average annual precipitation total for Seattle is 37.07 inches. The rainy season in Seattle doesn't officially begin until Ocotber 1. This leads into winter, which is the wettest season. Surprisingly, Seattle only has a mean annual snowfall of 7.1 inches -- it snows in the surrounding mountains. Spring in Seattle is mild and green, but like anywhere, can be very wet at times. Summers in Seattle are usually warm, dry, and sunny, with long days (because of its latitude) and cool nights. The driest time of the year in Seattle is the last half of July and the first half of August. The warm, mild weather often continues into fall, with cooler temperatures at night. A13, A14





By Road

Seattle has a very good bus system that travels all throughout the city and surrounding areas. It is serviced by Greyhound and Gray Line of Seattle within the city. A22


Interstate 5 – Goes north/south through the city of Seattle thereby connecting it to suburbs to the north and south of the city. Interstate 5 connects many of the major west coast cities to Seattle including; Los Angeles, Portland, Sacramento, San Diego, San Francisco, and Vancouver, Canada. A23


State Route 99/Alaskan Way Viaduct – Also goes north/south through the city of Seattle, however the state route is limited to the state of Washington so while it connects Seattle to its suburbs. State route 99 is a local highway so it doesn't connect it to other major cities on the west coast. The Alaskan Way Viaduct is a section of SR99 that is elevated and overlooks Elliott Bay. This makes the Alaskan Way Viaduct one of the more scenic routes of Seattle. There have been recent concerns that the Alaskan Way Viaduct may not be able to stand up to an earthquake and there is a legitimate chance that it will be shut down. Because of this there are several plans on ways to rebuild or replace the viaduct. A24


Interstate 90 – Goes east/west all the way across the country from Seattle to Boston and goes through cities like Chicago and Cleveland. Interstate 90 is the longest interstate in the country. A25



map of Seattle Area Road Map of the greater Seattle Area. A41


By Rail

King Street Station – King Street Station is the major train station in Seattle, which is serviced by Amtrak’s 12 Washington State trains and two Amtrak long distance trains. (Those being the Coast Starlight and the Empire Builder). A24


Seattle, WA : King Street Station King Street Station A42 


By Air

Seattle-Tacoma International Airport - Although there are some smaller airports in and around Seattle the primary passenger airport is the Seattle-Tacoma International Airport in SeaTac, Washington. Over 31 million travelers went through SeaTac airport in 2007. A26


By Sea

Seattle has the largest ferry system in the United States which services eight counties and 10 different routes in Washington. A24



Economics (Alake Kashyap)





Seattle has a history of boom and bust cycles, which usually happens with cities that are as large as Seattle [A17]. Seattle has risen as a company town (A company town is a town or city in which most or all real estate, buildings, utilities, hospitals, small businesses such as grocery stores and gas stations, and other necessities or luxuries of life within its borders are owned by a single company), then gone into abrupt decline, but it has typically used those periods to successfully rebuild infrastructure A17.


In 2006, Expansion Magazine ranked Seattle among the top 10 metropolitan areas in the nation for climates favorable to business expansion and one of the top 20 cities to live in [A18]. In fact, five companies on the 2006 Fortune 500 companies have headquarters in Seattle [A19] Among those are Washington Mutual, Amazon.com, Nordstrom, Starbucks, and Safeco. Boeing used to be the largest company in Seattle, but relocated its headquarters to Chicago.


During World War II, Seattle was the major point of departure for troops leaving for the North Pacific, and Boeing manufactured a lot of the war's bombers (aircrafts). The local economy fell after the war, but climbed after a period with the expansion of Boeing. The climb ws due to the growth of the commercial aviation industry. When this cycle went into a downturn in the late 1960s and early 1970s, many people left the area to look for work somewhere else in the US. It got to a point where local real estate agents put up a billboard that read "Will the last person leaving Seattle – Turn out the lights." [A20]




Technology companies, including Microsoft, Amazon.com, Real Networks, McCaw Cellular, T-Mobile USA, and biomedical corporations such as HeartStream, Heart Technologies, Physio-Control, Medtronic, ICOS, and Immunex, are located in Seattle.. This success produced an increase of new citizens with a population increase within city limits of close to 50,000 between the 1990 and 2000 Census. Seattle's real estate become some of the most expensive in the country. In 2005, Forbes ranked Seattle as the most expensive American city for buying a house based on the local income levels. A21








        Coniferous Forest                                            Harbour Seal                                          Black-Tailed Deer                             The Puget Sound



Before it was cultivated and settled, the Seattle area was characterized by dense coniferous forests most commonly made up of western red cedar, western hemlock, and Douglas-fir. Animal species native to this area include raccoon, sea otter, mink, coyote, black-tailed deer, and the harbour seal. Some birds native to the are are the turkey vulture, bald eagle, blue grouse, seabirds, shorebirds, and waterfowl.



Currently, only about 5% of the original habitat remains due to heavy population growth and urbanization in the area. The ecoregion has therefore been given a conservation status of critical or endangered.A28


Washington's soil is known as Tokul soil. This soil is found west of the Cascade Mountains in the Puget Trough. They extend from south of Seattle up to Canada. Tokul soils, made from volcanic ash, support the coniferous forests present in Washington.A29


Washington is also undertaking a project to restore Seattle's main source of water, The Puget Sound. Along with help of several local governments steps are being taken to improve the aquatic ecosystem of The Puget Sound. Oxygen levels in the water have become so low from chemical pollution that marine life such as fish, crab, sea stars, wolfeels, and octpi are suffocating. In May 2007 The Puget Sound Partnership was formed. This organization was created by the Governor of Washigton in order to create an agenda for actions to save the delicate ecosystem.A32




Land Usage and Other Information


Surrounded by mountains and water, the greater Seattle area features picture-perfect views and abundant recreational opportunities year-round. The city is 84 squares miles in size and has around 6,900 people per square mile. The population of the urban city of Seattle is 569,101 while the entire metropolitan area has a population around 3 million. The metropolitan area also includes cities like Tacoma, Bellevue, and Everett. Seattle is a member of King County, Washington which covers 2,126 square miles of land and also 180.5 square miles of water.A30 Seattle is home to 430 parks which occupies approxametly 6,200 acres or 11% of the cities land area. The largest park in the area is Discovery park which spans 534 acres. The oldest park in the city is Denny Park which was first opened in 1884. A43  Seattle, Washingson is also home to a 3 1/2 acre Japanese Garden National Park. The park features several tea events over the summer. A44 A vast majority of Seattle's land use does not actually occur on land but on the water. One of major commodity exports in the area are fish.A31 









A1 - http://www.hoteldeca.com/assets/03A5EA32-693D-4D73-9F45-2999873FF6AB.jpg








A8 - http://www.flatrock.org.nz/topics/environment/assets/mt_rainer_clouds.jpg

A9- http://en.wikipedia.org/wiki/Image:Seattle_07752.JPG (Image taken by a Wikipedia user)

A10- http://www.exhibits.pacsci.org/puget_sound/PSGeology.html

A11- http://cses.washington.edu/cig/figures/web_pnwtopo1_BIG.jpg

A12- http://factfinder.census.gov/servlet/ACSSAFFFacts?_event=Search&geo_id=&_geoContext=&_street=&_county=seattle&_cityTown=seattle&_state=&_zip=&_lang=en&_sse=on&pctxt=fph&pgsl=010">http://factfinder.census.gov/servlet/ACSSAFFFacts?_event=Search&geo_id=&_geoContext=&_street=&_county=seattle&_cityTown=seattle&_state=&_zip=&_lang=en&_sse=on&pctxt=fph&pgsl=010



A15- http://www.seattle.gov/transportation/steepest.htm

A16- http://dnr.metrokc.gov/wlr/Waterres/lakes/biolake.htm

A17- http://www.villagelife.org/news/archives/5-20-97_rebuildingSeattle.html

A18- http://www.butlercounty.biz/PDF_files/Press_Releases/2006_Americas_Hottest_City.pdf

A19- http://www.visitseattle.org/media/pkHistory.asp

A20- http://www.historylink.org/essays/output.cfm?file_id=1287

A21- http://seattletimes.nwsource.com/html/realestate/2002446059_homeprices21.html?syndication=rss&source=realestate.xml&items=7

A22- http://www.seattle.gov

A23- http://www.fhwa.dot.gov/reports/routefinder/table1.cfm

A24- http://www.wsdot.wa.gov/

A25- http://www.interstate-guide.com

A26- http://www.portseattle.org/seatac/

A27- http://www.pacificnaturetours.com/images/ForestLight.jpg

A28- http://www.city-data.com/city/Seattle-Washington.html http://www.nationalgeographic.com/wildworld/terrestrial.html?id=1&mapServiceName=WW_Terrecos&locWidth=120&locHeight=72&cMinx=-122.436232&cMiny=47.495375&cMaxx=-122.224659&cMaxy=47.734561&size=undefined&detail=undefined

A29- http://soils.usda.gov/gallery/state_soils/#list

A29 - http://www.cityofseattle.net/oir/datasheet/location.htm

A30- http://www.city-data.com/county/King_County-WA.html

A31- http://www.fishing.about.com/b/2006/02/09/seattle-area-fishing-report.htm

A32- http://www.ecy.wa.gov/puget_sound/Overview.html

A34 - http://www.homepage.montana.edu/~escicrs/geog411/geog411_advancedGIS_files/geog411_WebProjects_s07/ProjectFiles/web_parker/MountRainerLaharFlow.bmp

A35 - http://volcano.und.edu/vwdocs/volc_images/img_rainier.html

A36 - http://www.emporia.edu/earthsci/student/zellers1/rainier.htm

A37 - http://www.3dsquared.com/imagesl/pan/MarcA/Summer-Dawn.jpg

A38 - http://images.google.com/imgres?imgurl=http://upload.wikimedia.org/wikipedia/commons/thumb/7/73/Harbour_seal.jpg/800px-Harbour_seal.jpg&imgrefurl=http://commons.wikimedia.org/wiki/Image:Harbour_seal.jpg&h=529&w=800&sz=70&hl=en&start=1&sig2=szgU1JlY5GHXb-FeVv4nIQ&um=1&tbnid=GaeODe8iaK0RJM:&tbnh=95&tbnw=143&ei=wJ_9R6zKAqjmigHjypGEAQ&prev=/images%3Fq%3Dharbour%2Bseal%2Bimages%26um%3D1%26hl%3Den%26client%3Dfirefox-a%26rls%3Dorg.mozilla:en-US:official


A39 - http://cache.eb.com/eb/image?id=65530&rendTypeId=4

A40 - http://www.acm.vt.edu/~jchen/photoAlbum/Seattle/Space%20Needle%20-%20Puget%20Sound.jpg

A41 - http://www.aaccessmaps.com/show/map/seattle_overview

A42 - www.city-data.com/picfilesc/picc31049.php

A43- http://www.seattle.gov/parks/quickfacts.htm#parks

A44- www.seattle.gov/parks/parkspaces/japanesegarden.htm

http://www.komotv.com/news/10686711.html" class="WikiLink">A45 - http://www.komotv.com/news/10686711.html

http://www.blueprintforsafety.org/hail/hformation.aspx#top" class="WikiLink">A46 - http://www.blueprintforsafety.org/hail/hformation.aspx#top


Meterological Occurances in Seattle



By Steve Nowicki




                                                                                             Lightning over the Puget Sound  [B1]




Thunderstorms occur frequently north and south of Seattle due to the Puget Sound Convergence Zone, but the city of Seattle sees only the occasional summer thunderstorm.  Because of this lightning is a rarity for the city itself, but it can be seen in the distance in the convergence zone as shown above throughout the summer months. [B10]




 There are many hypothesis regarding the formation of lightning, however the most prominent include Interface and Induction Charging.


Interface Charging


 Interface charging deals with ice formations that exist within a thunderstorm cloud, and there are two types that are involved; small ice crystals and hailstones.  Since these two formations are formed by different processes and are different sizes, they have different electrical charges.  This difference in charge creates an electrical field between the two formations such that when the two collide, electrons will be transferred from the small ice crystal to the hailstone.  Following this transfer, the small ice crystal will be left with a positive charge and will be swept up to the top of the cloud by the storms updraft and the heavier hailstone will continue to fall with a negative charge.  This leaves the thunderstorm cloud with a positive top and a negative bottom.  This difference in charge between cloud regions is what generates lightning. [B8]


Induction Charging


Induction Charging is a feedback mechanism that reinforces and accelerates interface charging.  As interface charging creates an electrical field within the cloud, protons within each ice particle will migrate to the top of the particle and electrons will migrate towards the bottom.  This arrangement enhances interface charging. [B8]


When Lightning Strikes


Lightning occurs because regions of the thunderstorm cloud become extremely positive or negative and contain a lot of energy.  These regions either have protons or electons that are attracted to their opposite charge, and when they find them a lot of energy is transferred, creating the lightning bolt.  Lightning can occur within a cloud itself, from cloud to cloud, or from cloud to ground.  When lightning strikes the ground, protons or electrons are connecting with positive or negative regions of the ground.




                          Lightning formation [B9]                                                                                                     Interface Charging enhanced by Induction





 Lasting Impacts


The amount of energy within in a lightning bolt is simply enormous.  The current within the bolt contains between 15,000 and 30,000 amperes and bolt temperatures are five times greater than the surface of the sun.  Obviously whatever lightning strikes it will destroy.  Seattle only occasionally experiences lightning, but its deadliness is for the most part prevented by lightning rods on the city's skyscrapers. [B8]



                                                                                                 What lightning can do [B11]







Drought Case Study Mark Baker - mpbaker2



A drought is an extended period of time of persistently dry weather that can cause serious economic concerns such as crop damage and shortages in water supply.  Size, moisture deficiency, and duration are all factors considered into the severity of a drought. [B2]


Droughts are the most deadly natural disaster worldwide.  Droughts are different in all different regions.  What may be typical weather conditions in one area may be disastrous conditions elsewhere.   There are actually four different types of droughts: meteorological, agricultural, hydrological, and socioeconomic.  


Meteorological drought – A measure of the break off of normal precipitation levels for a certain area. 


Agricultural drought – When the amount of moisture in the ground is no longer sufficient for a certain type of crop to exist. 


Hydrological drought – When surface and subsurface water supplies are below normal. 


Socioeconomic drought – A situation that occurs when a decrease in water supply begins to affect people’s lives. [B2]






The picture above shows the current drought index for Seattle, WA.  As you can see, there is no sign of a drought through the entire state. 


Case: Seattle Drought of 2001


In 2001, Seattle experienced their second worst drought in the past 75 years.  A huge portion of Seattle’s power comes from a city hydroelectric system.  They use the force of falling water from rain, streams, and snow packs to create power.  “Water is literally the fuel that runs our generators.” [B3] 


The chart below shows the cumulative rainfall for Seattle and it’s surrounding regions that affect the hydroelectric power plants.  The dotted line shows the average over the past 40 years, the green line shows where the region is at currently, in 2008, and the tan line shows the numbers for 2001. 





The drought of 2001 brought many problems among the people of Seattle, making this clearly a socioeconomic drought.  The Department of Health received complaints from nine large utility companies saying that the drought was very likely to affect them.  At this point, Governor Gary Locke declared an energy alert and pleaded that residents and businesses alike try to reduce their energy usage by 10%. This was coupled by the increase in price for the utilities people used. [B4] 


By the end of 2001 there had been 57 emergency water right permits and changes of existing water rights. 75,000 acres of land used for farming had been shut out of commission, 25,000 acres of orchards had been pulled out, and the entire sugar beet industry was out of production. [B4] 


On September 5th, 2001, Seattle finally stopped asking for additional, voluntary water reductions, which was set forth on April 1st and supposed to last until November.  Over the course of the summer, residents and businesses had saved nearly 4 billion gallons of water from the regulations set.  The summer is typically the time when demand is highest, but residents cut back water use by 15%  [B5] 



Eastern Washington was hit the hardest by the drought of 2001.  [B4]  This makes sense because of Seattle’s location, a severe drought is quite uncommon.  Placed conveniently to the east of the Puget Sound, and west of the Cascade Mountains, Seattle typically gets dumped with rain due to the constant rising of air over the Cascades.  However, the 2001 drought wasn’t the first of its nature, as it was hit even harder in 1977. [B4]



                             THUNDERSTORMS bemoras2

FREQUENCY-   While rain is very prevalant in Seattle, thunderstorms are rather uncommon. The National Oceanaic and Atmospheric Administration only has a record of 8 reported cases thunderstorms and high winds since 1950 in the King County area.[B13] While Seattle experiences very rare cases of thunderstorms, they are very prevalant in the areas north and south of Seattle due to the Puget Sound Conversion Zone. [B10]






FORMATION- All types of sever thunderstorms require the same four basic elements in order to form. 1) A source of moisture 2) a condtionally unstable atmosphere 3) a mechanism to trigger the thunderstorm's updraft (this can occur either through lifting or heating of the surface) 4) vertical wind shear. There are however, expections to these elements. For example, an airmass thunderstorm can form in the absence of a vertical wind shear. this thunderstorms are also known as isolated thunderstorms and tend to last for only a few hours. There are also Mesoscale Convection Systems. These storms are known for this damaging straight-line winds and heavy rainfall. Frontall Squall Line storms are the largest of all thunderstorms with the squall line stretching hundrerds of kilometers long. Finally, there are supercells. These are by far the most damaging and severe type of thunderstorm there is. The unique thing the storms is that due to its circulation, it behaves as one large storm rather than smaller storm cells. [B8]



[B15] [B16]





LASTING EFFECTS- The are numerous lasting effects of thunderstorms due to what accomapny thunderstorms. Most thunderstorms are accompanied with lightinging with has enough electrical engery to burn 5 times hotter than the surface of the sun. High winds also frequent thunderstorms. Winds gusting to high speeds can knock over trips, toss debry and damage homes. It is also a possibilty for tornados or microbursts to develop out of thunderstorms. High property damage and human casualties can occur from what develop out of thunderstorms. The largest amount of damage recorded by a thunderstorm on Seattle adds up to $25,000.[B13]




Amanda Lerner (alerner2)



A tornado is defined as a violently rotating column of air extending from a thunderstorm to the ground. They often develop out of severe thunderstorms. Below is a description of the stages of formation of a tornado. [B18]

 Before thunderstorms develop, a change in wind direction and an increase in wind speed with increasing height creates an invisible, horizontal spinning effect in the lower atmosphere.

 Rising air within the thunderstorm updraft tilts the rotating air from horizontal to vertical.

 An area of rotation, 2-6 miles wide, now extends through much of the storm. Most strong and violent tornadoes form within this area of strong rotation.

Woodward OK (Ron Przybylinski)

 A lower cloud base in the center of the photograph identifies an area of rotation known as a rotating wall cloud. This area is often nearly rain-free. Note rain in the background.

Woodward OK (Ron Przybylinski)

 Moments later a strong tornado develops in this area. Softball-size hail and damaging "straight-line" winds also occurred with this storm. [B18]


The Puget Sound Convergence Zone, an area where wind blown in from the ocean and split by the Olympic Mountain range converges, also contributes to the formation of tornadoes in the Seattle area. [B20] Some tornadoes can also develop out of waterspouts. A waterspout is a weak tornado that develops over water and can sometimes move inland and become tornado. [B18] 


Although the probability of tornadoes striking Seattle are very weak, it is not impossible. The National Weather Service believes that tornadoes are actually under-reported in the Northwest, due in part to a common belief that tornadoes do not occur in this region. In recent years, with a growing population, more reports have been made. Below is a chart of major tornado incidents reported in Seattle and the surrounding areas.


Currently, Seattle does not have an audible warning system to alert inhabitants of tornadoes, except along the waterfront. [B17]  Western Washington experiences only a few tornadoes each year. Tornadoes are associated with a few changes that can act as warning signs, though, such as dark, greenish skies, large hail, a wall cloud, a loud roar, and heavy storms. [B18] The last major tornado in Western Washington touched down in Vancouver on April 5th, 1972, and killed six people. [B19]


Major Incidents [B17]







King County


Four F0 tornadoes confirmed in western King County. None caused damage.


Vancouver, WA


This region storm demonstrates that deadly tornadoes have happened in the Northwest. An F2 tornado developed as part of a regional windstorm near Portland, Oregon. It moved across the Columbia River and killed six people, injured 300 more and caused $6 million in damage in Vancouver, Washington on April 5, 1972.




A tornado (F3) in South King County topples signs and damages buildings causing $500,000 in damage. This tornado occurred during a regional windstorm. It started as a waterspout then moved inland.




The area's first confirmed tornado (F1) touches down west of Sand Point, severely damaging several homes. It picked up a carport and tossed it down onto the neighboring house. Everyone in the house was caught by surprise, but there were no casualties.



Case Study:

First Recorded Tornado in Seattle

September 28, 1962




On September 28, 1962 at approximately 5:55 p.m. a witness saw two clouds merge into a funnel and reach the ground, bringing with it 100 m.p.h. winds. Nicknamed "Bouncing Betty" by the locals, the tornado first hit near the Sand point area of Seattle, and in 15 minutes traveled across Lake Washington to Juanita. The tornado damaged eight homes in Sand Point, formed a 100 foot high waterspout over Lake Washington, and finally toppled 70 trees when it hit Juanita. Many fences, roofs, and cars were damaged by debris but no fatal injuries were recorded. After about 15 minutes, the funnel cloud spun back into a mass of gray clouds that was otherwise a typical late summer storm.


Strong thunderstorms are common in the Seattle area, but the tornadoes that can sometimes develop are not. Given that so many bodies of water surround Seattle, it is a common misconception that tornados cannot affect the area. The tornado of 1962 illustrates this point because it was not well forecasted. Many residents, instead of taking precautionary safety steps, watched in amazement as the tornado passed through their towns. Although there were no fatal injuries, there were some damages to personal property. [B21]


If nothing else, the 1962 tornado acted as a warning to residents of the area. Although tornadoes are uncommon in the Seattle area, they are not impossible. This was the first recorded tornado in Seattle's history but it was not the last.


 Mountain Snowstorms


Despite its geographical position directly south from Canada, Seattle does not receive too many snowstorms in general. The most snow storms occur during the month of September, where Seattle averages 1.8 inches. By the time that March rolls around, the average snowfall fall in is around .3 inches. [B23].  On average, Seattle will have one to two snowstorms a year. The majority of snowstorms occur in the Cascade Mountains of Washington. Extratropical cyclones, particularly systems that develop in the Pacific Ocean, are responsible for mountain snowstorms in the western US. Yet, because of the scarcity of thunderstorms in the city of Seattle, when even a couple inches fall, traffic becomes devastatingly dangerous compared with other cities that expect lots of snow each winter. (Montreal, Detroit, Minneapolis)


Of course one of the major devastations associated with mountain snowstorms are avalanches. The Cascade Range receives extensive precipitation due to its size and orientation to the flow of Pacific marine air. In this type of maritime climate, it is common for air temperatures to rise above freezing and for precipitation to change from snow to rain during mid-winter storm cycles. Temperatures can change several degrees within minutes, thus causing abrupt changes in precipitation type. These conditions frequently cause the release of avalanches. [B24].


Just a few months ago, December, 2007, a snowshoer vanished in an avalanche that struck Mt. Rainier. In the week leading up to the avalanche, over 5 feet of snow fell onto the mountain. However, the danger of an avalanche was deemed “considerable” on that cold day in December, so hikers were still allowed to roam the mountain’s trails. However, out of nowhere an avalanche swept up a snowshoer while his friend watched from a higher-up spot. The friend began digging and digging but failed to find his friend buried in the several-foot high pack of snow covering thousands of square feet. In 2007, 5 people died because of an avalanche in the Cascade Mountains. [B25] Thus, mountain snowstorms are definitely considered a severe and sometimes fatal weather condition.


[B26]  "Avalanche in Motion"




Floods (alake kashyap)





Since 1993, there have been four major floods in the Seattle area. The biggest being in Snoqualmie Falls. A Pacific weather system brought large amounts of rainfall from November 2 through 7. This caused flooding until November 11th. This storm caused 104 homes to be destroyed, 206 homes with major damage, and 572 received minor damage. In total, this storm costed 11.1 million dollars in property damage. That accounts for 45.3% of the total cost of all floods in Seattle since 1993 [B27].



Below is a clip of Snoeualmie Falls during its flooding stage.

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 [B28]                                                                                                  pictured above, flood damage to a town South of Seattle [B32, B33]


Time of the year floods occur

Floods in the Seattle area tend to occur later in the year, contrary what many people think (that flooding usually occurs in the Spring). Looking at the data over the past 15 years, 75% of the floods that have taken place in the Seattle area have been in September or later. In fact, the most damaging flood (Snoeualmie Falls) took place in November, as mentioned above [B27]


How floods develop meteorlogically

How floods develop meteorologically is fairly simple. It usually takes a thunderstorm to produce floods, but it can also be caused by non-stop continuous rain over an extended period of time. Rain plays a role in the hydrologic cycle in which moisture from the oceans evaporates, condenses into drops, precipitates (falls) from the sky, and eventually returns to the ocean via rivers and streams to repeat the cycle again. However if the rain continues to fall over an extended period of time, or very rapidly over a short period of time, floods have a very good chance of taking place [B32]



Lasting Impacts

Below I have posted two examples of what type of damage and lasting impacts floods can do to the Seattle area. the videos below are from storms that have caused major flooding in the metropolitan Seattle area.


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 [B29, B30]

Unique Aspects

There are a few unique aspect to floods and the Seattle area. First, I found it quite surprising that the amount of floods that occured were not much higher. Seattle has a reputation for being a city where it rains constantly. To have found only 4 major floods in the past 15 years really caught me off guard. I did notice that since 1993, there have been 227 recorded floods in all of Washington [B27]. The most expensive flood occured in Lewis County, totaling 50 million dollars, or 20% of all costs of the 227 recorded floods combined.


Below, a few images of what floods have done as far as damage goes in the Seattle area [B32, B33]






Brian Bajjalieh (bbajjal2)


Hail is a common occurrence in severe thunderstorms however severe thunderstorms are not a common occurrence in Seattle, Washington. Seattle gets thunderstorms but they rarely become severe because they are not able to get strong like they do in the Midwest and thus the occurrence of hail is not that often [B34].  The main reason that thunderstorms do not become so strong in the Northwest is because the ocean stays a constant 50-55 ºF year around [B34]. This has affects on the air coming inland making it warmer or cooler (depending on the time of year). Because the severity of thunderstorms depends on the instability of air, the storms stay relatively weak because the temperature change as the air rises is not as great which means that the air will not get to unstable. However, occasionally cold air will sweep in and if you mix this with the mountainous topography of Seattle, severe thunderstorms can and will form.





        Hail is formed when there are up drafts of warm air and down drafts of cold air present in severe thunderstorms. If the downdraft temperature is below 32ºF, raindrops will freeze [B35]. The frozen raindrops can repeat this cycle many times and with each time the drop will warm and refreeze getting larger and larger with each pass and once the now hailstone is heavier than the force of the updraft it will fall to the ground [B35].



Aspects and Impacts         

        Hail is not very unique nor does it have lasting impacts to Seattle. It is unique in that it happens seldom. Most impacts from this event are immediate affects such as property damage. Hail can be very destructive to roofing, cars, and humans if one was unfortunate enough to be caught outside during a hailstorm.




Wind Storms

by: cwendt


The strongest wind events in Puget Sound and the Seattle area typically occur in the fall and wintertime when many storms tend to make landfall across the southern tip of Vancouver Island or the northern tip of Washington State. As the storms track inland, it creates a direct wind path to the low-lying Puget Sound area. The winds are enhanced by the topography here, the Olympic Mountains to the west and the Cascade Mountains to the east, or the I-5 corridor (named as such for Interstate 5 that runs north-south through the area). The storm creates a low pressure to the north, and the higher pressure air to the south races up the corridor and is essentially "squeezed" by the mountains on both sides, accelerating the air as it moves up the corridor.





Seattle is right in the middle of this corridor and receives strong winds anytime a storm comes inland in this way. The speed of the winds depends on the strength of the storm, the track, how strong the pressure gradient, etc. Winds can also be blown over the Cascade Mountains creating strong gusts in the Puget Sound area.




These winds can topple trees, downing phone and power lines and wreaking havoc on cars, homes, and businesses. These create long delays and detours and can cause major monetary damage. [B36, B37, B38]


Case Study - Hanukkah Eve Wind Storm of 2006 - Scott Manson - manson2


The Hanukkah Eve Wind Storm occured on December 14th of 2006 and dissipated on the 15th. It was a Pacific storm that hit the northwest coast of the United States, directly impacting Seattle and the surrounding area. The storm was extremely damaging not only from winds but also the heavy rain associated with the storm. This led to much flooding in the lower laying areas around Seattle. Thousands of trees were uprooted which caused damage to houses, power lines (which resulted in the loss of power to over one million people.) There were a total of 15 fatalities in the Seattle area, only four of which were as a direct result of the wind storm. The others died later due to complications that arose out of the wind storm.  This windstorm formed on the 13th of December, giving only a day to forcast the event before it hit into the West Coast of the United States. The storm was fairly typical although windstorms in the Western part of the country are typically east of the Rocky Mountains and are Chinook type windstorms. This windstorm was typical in terms of the type of effects and windspeeds. Wind gusts reached over 100 miles per hour with also very high sustained wind speeds. The amount of rainfall was perhaps atypical because while associated with windstorms, the amount of rain in some areas during this windstorm set unprecedented records. The implications for Seattle and the surrounding area were devastating. As mentioned previously there were numerous fatalities along with over 250 hospitalizations for other injuries. Between Washington and Oregon there were 220 million dollars of insured damages to structures. Due to this storm Seattle and the surrounding area examined how to better prepare for an event of this nature in the future. [B42] [B43]





Heat Waves - Scott Manson - manson2




Heat waves are periods of unusually hot weather for a given period of time. The reason this definition is vague is because heat waves are defined differently depending on certain areas of the United States.


The National Weather Service will issue a heat advisory in the Western United States (Seattle Region) if the maximum heat index is 98°F to 105°F for 24 hours or longer between May 1 and June 30. Between July 1 and September 30 the required heat index must be between 100°F and 105°F for the same period of time to issue a heat advisory. For a excessive heat warning from the National Weather Service, Seattle must have either a maximum heat index of 106°F or higher for 3 or more hours on back to back days and a minimum heat index of no less than 90°F at night, or a maximum heat index of 115°F or higher regardless of duration. To clarify heat index differs from air temperature in that it takes relative humidity into consideration. As the relative humidity and/or air temperature increase the heat index will increase as well. Heat index is a measure of heat stress on the human body. [B8]




Frequency of Heat Waves in Seattle


Seattle typically has relatively cool summer temperatures due to the position of Seattle on the Pacific Ocean. Typically the position of the jetstream will be north of the area effected by a heat wave, which is rarely the case when looking at Seattle. Due to these aspects heat waves are relatively rare in Seattle; however it also means that they are not as prepared for heat waves when they occur. Heat has typically been one of the more devastating weather-related causes of death in the United States. [B8]


Development of Heat Waves


There are many factors that contribute to the development of a heat wave. The first perhaps being the most obvious is the absence of polar air masses that can move into the region. Typically Seattle will have cold air coming in from the north which will provide a cool front in the summer. With the absence of this, the region will remain unusually warm. The extreme heating of the surface contributes to the development of heat waves. This occurs when there is very little cloud cover which leads to an increase in the air temperature and therefore a high heat index. Dry ground goes hand in hand with this concept in that it prevents cloud formation from evaporation, and it leads to heating of the air temperature near the surface. Finally the absence of vertical mixing of air ensures that cooler, drier air remains aloft and warmer, moister air remains near the surface which of course results in a higher heat index near the surface.  [B8] [B40]


Unique Aspects of Heat Waves in Seattle


Seattle, like all metropolitan areas, suffers from the Urban Heat Island Effect. The Urban Heat Island Effect explains the difference in temperatures in rural versus urban areas. Urban areas are generally warmer for several reasons. First of all evaporative cooling cannot occur in many urban areas because those particular areas are paved. In paved areas soil moisture is not available and therefore evaporative cooling cannot occur. Secondly, heat is absorbed into building materials and asphalt more readily than in the natural ground which contributes to the higher air temperature. (This is why walking on concrete in the summer hurts more than walking on grass.) Seattle is also unique in that they generally have more moist weather, which means the heat index may be higher than in other areas without as much humidity. Seattle is unique in that regard because they do not necessarily need air temperatures to be as high as other places in order to have a heat wave. [B8]


Lasting Impact from Heat Waves
Heat waves typically have few long term effects because they do not create much physical damage to structures. The biggest impact heat has is the stress on humans. Heat waves cause the most weather-related fatalities in the United States. Other than fatalities heat waves can cause sunburn, heat cramps, heat exhaustion, and heat stroke. The lasting impact of heat waves are the health issues it creates rather than the damage it does to property or geographical areas. [B8][B40]




[B1] - http://bobqat.com/Mazama/Sky/013.html

[B2] - http://www.wrh.noaa.gov/fgz/science/drought.php?wfo=fgz

[B3] - http://www.ci.seattle.wa.us/light/ctracks.html

[B4] - http://www.ecy.wa.gov/news/20501news/2001-081.html

[B5] - http://seattlepi.nwsource.com/local/37701_drought05.shtml

[B6] - http://www.drought.unl.edu/dm/DM_state.htm?WA,W

[B7] - http://www.ci.seattle.wa.us/light/ctracks.html

[B8] - Charlevoix, Rauber, and Walsh. Severe and Hazardous Weather

[B9] - http://www.fas.org/irp/imint/docs/rst/Sect14/Sect14_1d.html

[B10] - http://www.cityofseattle.net/html/visitor/weather.htm

[B11] - http://upload.wikimedia.org/wikipedia/commons/thumb/6/67/Lightning_damage.jpg/800px-Lightning_damage.jpg

[B12]- http://z.about.com/d/saltfishing/1/0/X/1/clouds2.jpg

[B13]- http://www4.ncdc.noaa.gov/cgi-win/wwcgi.dll?wwevent~storms

[B14]- http://earthstorm.mesonet.org/materials/graphics/TstormFreq.gif


[B16]- http://www.ux1.eiu.edu/~jpstimac/1400/FIG10_003.JPG

[B17] - http://www.seattle.gov/emergency/hazards/tornadoes.htm

[B18] - http://www.nssl.noaa.gov/edu/safety/tornadoguide.html

[B19] - http://www.komotv.com/news/archive/4009171.html

[B20] - http://www.komotv.com/news/archive/4009171.html

[B21] - http://www.historylink.org/essays/output.cfm?file_id=886

[B22] - http://starryskies.com/Artshtml/dln/4-00/tornado05.jpg

[B23] - http://metrokc.gov/prepare/docs/HIVA/SevereWeather.pdf

[B24] - http://www.pep-c.org/avalanches/

[B25] - http://www.topix.com/outdoors/2007/12/avalanche-on-mount-rainier-buries-climber


[B26] - http://nsidc.org/snow/gallery/avalanche.jpg

[B27] - http://www4.ncdc.noaa.gov/cgi-win/wwcgi.dll?wwEvent~Storms~WA~king~flood

[B28] - http://www.youtube.com/watch?v=LGm4kzM3358

[B29] - http://www.youtube.com/watch?v=HTxmnf3o_Bs

[B30] - http://www.youtube.com/watch?v=tP-THaSNufo

[B31] - http://www4.ncdc.noaa.gov/cgi-win/wwcgi.dll?wwEvent~Storms~WA~*All~flood

[B32] - http://seattlepi.nwsource.com/local/342450_cityflood06.html


[B33] - http://newschomp.blogspot.com/2007/12/centralia-chehalis-washington-i-5-south.html

[B34] - http://www.komotv.com/news/10686711.html

[B35] - http://www.blueprintforsafety.org/hail/hformation.aspx#top

[B36] - http://www.komotv.com/weather/faq/4306592.html

[B37] - http://www.komotv.com/weather/faq/4347056.html

[B38] - http://seattlepi.nwsource.com/local/296085_winda15ww.html

[B39] - http://www.co.okaloosa.fl.us/images/safety/heatindex.gif

[B40] - http://www.fema.gov/areyouready/heat.shtm

[B41] - http://seattletimes.nwsource.com/ABPub/2007/12/13/2004069934.jpg

[B42] - http://www.wrh.noaa.gov/sew/Windstorm_announcement.php

[B43] - http://www.nwac.us/documents/annual_reports/NWAC_Annual_Report_June_2007


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