Sunday, July 26, 2009
Thunderstorms and the Upcoming Major Heat Wave
Last night there was some thunderstorms and rain from the central Sound northward associated with an upper level low/trough over the region (see upper level chart and radar image above and below). The action was greater to the north, particularly over southern British Columbia. Air rotates counterclockwise around lows and convection forming to the northeast rotated into BC and northern western Washington. But there wasn't enough rain to make a difference. As the trough/low moves out it sets the stage for the big action this week--a major, multi-day heat wave (my book has several sections on thermal troughs and their importance if you are interested). As I will describe below, we could have several days in the 90s and some locations in the south Sound could hit 100F.
Heat waves actually are the most dangerous weather phenomenon around the world...many more people die from them then hurricanes, tornadoes, and windstorms. And the elderly are the most vulnerable...particularly those without air conditioning (which includes most people in our region). So if you know some older folks in a hot apartment or house...it will be good to check on them. Long heat waves like this week allow time for buildings to heat up...which makes it all worse. But we have an advantage over most regions...our water stays cool and going to the shore of Puget Sound, the Strait or the Pacific brings cooler temps. And we don't have the high humidities like the eastern U.S. so sweating works well. And the dry air allows temperatures to cool at night. Another good reason to live in the NW!
Today (Sunday) will see temperatures getting into the upper 80s F for most of western Washington away from the water. During the week an upper level ridge will build over the region and high pressure will be strongest to the east. This will bring warm air aloft AND offshore (easterly) flow.....much more easterly flow than we have seen the past several weeks. This configuration brings downslope warming on the western slopes of the Cascades as air is compressed. With warm temperatures a thermal trough will build northward into western Washington...this is the pattern that gives us the highest temps. (see graphic for pressure prediction for Wednesday)
Looking at the latest computer models, it appears that we will warm progressively into mid-week and Wednesday or Thursday will be the warmest. High 80s today, lower 90s tomorrow, mid nineties on Tuesday, and upper 90s on Wednesday and Thursday--with some locations even higher each day (central and southern Sound on the east side). We could easily have five 90+ days in row--if we do so, we will tie the record for consecutive days above 90F in the Seattle record. If we beat 90F today, we could establish the record this week. (I am NOT hoping for this, I have to sleep at night too).
To get you "warmed up" for this event, I have placed below the computer forecasts for 5 PM on Wednesday and Thursday. The lightest colors are temps of 96-100F!
The surface is extraordinarily dry. I did not talk about the other issue...wildfires....but this is the kind of situation that can produce big fires west of the Cascades. People forget that the west can get huge fires...hopefully not this time. And there is one more threat in this purgatory of heat...high ozone values. Sustained warm temps in the 90s can produce very high ozone values...particularly on the lower slopes of the Cascades, which the nitrogen oxides of the city mix with the volatile organics emitted by vegetation (terpenes). Enumclaw and Pack Forest are often the worst spots.
The bottom line of all this is this is a very serious, and perhaps historic, heat wave.
Finally, let me note I will be speaking in Leavenworth on Friday evening if anyone is interested...see info on the side panel.
Posted by Cliff Mass at 7:52 AM