2009 Pacific Northwest heat wave
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The 2009 Pacific Northwest heat wave was a heat wave that affected the Pacific Northwest region of the United States and Canada in late July 2009, particularly areas west of the Cascade Mountains in British Columbia, Oregon and Washington. The heat wave set many new heat records across the area, and broke the previous all-time record high temperature in Seattle by three Fahrenheit degrees (1.7 Celsius degrees). Because the temperatures reached in the heat wave are rare in the Pacific Northwest, few residents own air conditioners.
Temperatures soared to record highs in late July from Medford, Oregon, to Seattle, Washington, and as far north as the Northwest Territories in Canada. The hottest weather occurred from July 26 to August 2, with the peak of the heat from July 28 to July 30. The high of 103 °F (39 °C) at Seattle-Tacoma International Airport on July 29 set the record for the hottest temperature ever in Seattle since records began in 1894, breaking the old record of 100 °F (38 °C) set on July 16, 1941, when the official weather station was located in downtown Seattle, and tied on July 20, 1994, at Seattle-Tacoma International Airport. Nighttime low temperatures were unusually high as well — in the upper 60s and lower 70s °F (about 21 °C). The morning of July 29, Seattle also set a new record warmest low temperature, 71 °F (22 °C), breaking the old record of 69 °F (21 °C) set on September 2, 1974, and tied a day earlier on July 28, 2009.
The heat was not confined to Seattle. Portland International Airport in Oregon reached 106 °F (41 °C) on two consecutive days on July 28 and 29, nearly tying the all-time record there of 107 °F (42 °C). Portland tied its warmest low temperature on record with a low of 74 °F (23 °C) on July 28. While the neighboring city of Vancouver, Washington, tied its all-time record high temperature of 107 °F (42 °C) on July 29.
Record temperatures were also recorded across the border in British Columbia where Vancouver International Airport saw two all time temperature records fall on July 29 and 30 when temperatures of 34.0 °C (93.2 °F) and 34.4 °C (93.9 °F) were recorded respectively. Abbotsford, British Columbia, in the Fraser Valley saw an all-time high when the temperature hit 38.0 °C (100.4 °F) on July 29. Vancouver Island also saw record temperatures which included Port Alberni reaching 40.0 °C (104.0 °F), Comox also saw a 48-year-old record fall when the temperature reached 35.2 °C (95.4 °F).
The heat was part of a summer that was overall very warm in the Northwest. Seattle recorded its second warmest July on record with an average temperature of 69.45 °F (20.81 °C), trailing only July 1941 (average temperature of 69.55 °F (20.86 °C)), and the third warmest month on record, trailing July 1941 and August 1967 (average temperature of 71.1 °F (21.7 °C)). The June 1 to July 31 time period was the warmest on record in Seattle with an average temperature of 66.7 °F (19.3 °C), besting the previous warmest June/July period of 1958 (average temperature of 66.4 °F (19.1 °C)).
Meteorological history leading up to the heat wave
In early July, the Global Forecast System (GFS) and European Centre for Medium-Range Weather Forecasts (ECMWF) models began showing a possible heat wave almost two weeks before the expected event. As the days passed, the models maintained an amazing trend with few changes. As of early Thursday, July 23, the models had the heat wave moving into the area on Saturday afternoon into Sunday, bringing historic highs for northwestern Oregon and southwestern Washington. The most severe heat wave in northwestern Oregon history was in August 1981, when the temperature reached 107 degrees at PDX. During that heat wave, temperatures soared to 100 °F or higher on four consecutive days. The last heat wave to bring three consecutive days of 100 °F-plus temperatures in the area was in 1994.
Early in the week of July 19, several meteorological computer forecast model solutions were forecasting an upper level low (ULL) to move from the central Pacific into the Northwest, and either retrograde to the west or move very slowly across the Northwest. However, model consistency was quite low at this point. By Thursday, July 23, models consistently depicted the ULL stalling over northeastern Washington throughout the weekend. This pushed back the heat wave until the following Monday. However, the area still appeared to be a lock for at least 3–5 days of 90 °F-plus weather. Late in the week, the North American Mesoscale Model (NAM) and GFS models were consistently forecasting the ULL to be kicked to the east by Monday morning, which allowed for a ridge of high pressure to build over Oregon and Washington, and for temperatures to soar to 100 °F or high in valleys east of the coast range.
The NWS Portland office issued an Excessive Heat Watch early Sunday morning.
Quote from 3am forecast discussion "..WITH 100 DEGREES POSSIBLE MONDAY IN THE HOTTER INLAND VALLEYS. TEMPERATURES APPEAR ONLY TO GET HOTTER TUE/WED AS THE RIDGE REMAINS OVERHEAD AND GFS/NAM/EC BRING 850 MB TEMPS IN THE VICINITY OF +25 TO +27 DEG C. WITH MOSTLY SUNNY SKIES AND THE ABSENCE OF ONSHORE FLOW...THIS AIR MASS COULD SUPPORT TEMPS PUSHING 105 DEGREES IN THE WILLAMETTE VALLEY. INDEED...LATEST NAM MOS GUIDANCE SHOWS SOME ASTRONOMICAL NUMBERS FOR HIGH TEMPS TUE...WITH HIGHS PUSHING 110 DEGREES IN THE CENTRAL AND SOUTHERN WILLAMETTE VALLEY. FOR NOW...OUR FORECAST HAS THE WARMEST HIGHS AROUND 102-104 IN THE WILLAMETTE VALLEY TUE/WED." 
Record highs began to tumble in Oregon and Washington on Monday, July 27. Portland International Airport eclipsed its old record for the date of 102 (set in 1958), reaching 103; Vancouver, Washington, beat its old record of 100 °F (set in 1998) by three degrees, also reaching 103. Although they fell shy of the records for July 27, several other localities topped the century mark on Monday, including: Salem, 103; Hillsboro, 103; McMinville, 103; downtown Portland, 102; Eugene, 102; and Hood River, 100.
As of August 3, statistics about victims from the heat wave are unknown. The first death related to the heat wave occurred on July 30.
Seattle's daily temperatures during the 2009 heat wave:
- Sunday, July 26: High 89 °F (32 °C), Low 61 °F (16 °C)
- Monday, July 27: High 94 °F (34 °C), Low 65 °F (18 °C)
- Tuesday, July 28: High 97 °F (36 °C), Low 69 °F (21 °C) (Tied July 28 high temperature record set in 1958 and tied in 1998 ... tied all-time warmest low temperature record set in 1974)
- Wednesday, July 29: High 103 °F (39 °C), Low 71 °F (22 °C) (Broke July 29 high temperature record set in 1971; broke all-time high temperature record set in 1941 and tied in 1994 ... Broke all-time warmest low temperature record set in 1974 and tied in 2009)
- Thursday, July 30: High 96 °F (36 °C), Low 62 °F (17 °C) (Broke July 30 high temperature record set in 1965)
- Friday, July 31: High 84 °F (29 °C), Low 58 °F (14 °C)
- Saturday, August 1: High 90 °F (32 °C), Low 57 °F (14 °C)
- Sunday, August 2: High 89 °F (32 °C), Low 60 °F (16 °C) (Tied August 2 high temperature record set in 1977)
Portland, Oregon's daily temperatures during the 2009 heat wave:
- Friday, July 24: High 85 °F (29 °C), Low 59 °F (15 °C)
- Saturday, July 25: High 90 °F (32 °C), Low 63 °F (17 °C)
- Sunday, July 26: High 93 °F (34 °C), Low 61 °F (16 °C)
- Monday, July 27: High 103 °F (39 °C), Low 68 °F (20 °C) (Broke July 27 record set in 1958)
- Tuesday, July 28: High 106 °F (41 °C), Low 74 °F (23 °C) (Broke July 28 record set in 1998, first time ever 106 in Portland)
- Wednesday, July 29: High 106 °F (41 °C), Low 71 °F (22 °C) (Broke July 29 record set in 2003)
- Thursday, July 30: High 96 °F (36 °C), Low 67 °F (19 °C)
- Friday, July 31: High 94 °F (34 °C), Low 62 °F (17 °C)
- Saturday, August 1: High 95 °F (35 °C), Low 63 °F (17 °C) (Broke August 1 record set in 1949 and tied in 1986)
- Sunday, August 2: High 94 °F (34 °C), Low 65 °F (18 °C)
Oregon City, Oregon, topped out at 108 °F (42 °C) on Wednesday, July 29.
- "Seattle hits 103 -- Welcome to the hottest day ever! | Local & Regional | Seattle News, Weather, Sports, Breaking News | KOMO News". Archived from the original on 2013-07-13. Retrieved 2013-07-04.
- Rick Bowmer. "Northwest Heat." AP Images. Press Association, Inc. 2009. Retrieved August 14, 2012, from HighBeam Research: http://www.highbeam.com/doc/1A2-d75bbcb9-91a0-4077-998a-e27b7c3ae83b.html
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