What the hell is happening?
Global warming plays a double role in this particular heat wave. The meteorologists at The Weather Network (Canada) note that this highly unusual heat bubble is courtesy of an unusually strong Pacific storm that is feeding warmer air into a dome of hot air. To this, add the extra flexibility of the storm track since the far North is being warmed faster than the temperate latitudes.
This is an unusual dome of hot air. It is centered in central British Columbia, and the 500 mb height tops out near 599 dam, but that the 599 reports southeast wind implies the center of the ridge is to its southwest and possibly higher. When such a dome shows up without a cool marine layer underneath, records are going to fall.
Temperatures at 850 mb can be used on sunny summer days to estimate the high temperature at sea level. They ranged from 23 C to 26 C at 0000Z (5 pm PDT). This time of year, the high temperature near sea level can be estimated by adding 13-17 C. This would mean 36 to 43 C, or 97 to 109 F.
Today Seattle saw highs of 97 F to 103 F, while the Portland area endured 105 to 109 F. Update: Portland’s official temperature hit 108 F today, the hottest day in Portland’s recorded history. The Puget Sound cities near I-5 broke their daily records by 12 F, while areas less likely to enjoy cooling from the Pacific tied or broke their records by smaller amounts. The rule-of thumb worked well in Portland, but not in Seattle. (That’s probably why NWS stations functional forecast offices all around the country. There is no human way to understand the effect of the local geography and land-use patterns for every locality in the country.)
Anyway, going into the future, let’s see how conditions will evolve 24 hours from now. 5 PM local time is about an hour after the daily high is usually measured.
First, the 500 mb
We see that the GFS has lobbed 20 m off the height of the ridge, which is a good thing. Unfortunately the GFS initialized the ridge 10 — 20 m too low, that is, it looked at the observations and concluded that the ridge was only 5980 m high when in fact it was 5990 or maybe even 6000 m high. Still, heights of 595 hPa supported 105 F in Indiana in 2012 and 598 hPa supported 108 F in LaCrosse, Wisconsin during the July 1995 killer heat wave, so 597 hPa is plenty.
Now on to the 850 hPa
Appealing to the initialization, it appears the initialization was maybe 1 — 2 C too warm. So instead of 27-34 C inland, we may only be dealing with 25.5 — 32.5 C inland. In short, the 850 hPa temps may only rise by 1.5 C near the Oregon coast, 3.0 C near Portland and Seattle and 5 C in areas seeing the greatest heating.
So, what supported 100 F weather in Seattle now supports 105 F. What supported 107 F in Portland now supports 112 F. Medford is not at sea level, so it will top out somewhere around 110 F instead of 117 F.
Also note the little low pressure analyzed near the California-Oregon Line. This is called a thermal trough. These frequently develop near the mouth of the Colorado River when a low area adjoining higher areas is strongly heated. As a low, it develops a circulation that come out of the east. It’s a weak circulation, but it will be drawing downslope winds into the Williamette Valley.
The high-resolution NAM is usually used for mesoscale events like derechos. It is 1-2 C conservative than the GFS. If this model verifies, Seattle sees 102 F, Portland 109 F and Medford 107 F.
An unwelcome development for the I-5 corridor is that it’s becoming apparent that the thermal ridge will not hop the Cascades until Tuesday, which would mean that whatever happens Sunday will repeat on Monday. NAM is extra-aggressive here south of Portland, which would mean that Portland would stay at 109 but Salem would break 110 F on Monday.
Environment Canada reported 43.3 C (109.9 F) in Lilooet, BC, roughly 110 miles north of the US border. I suspect that Canada will see its all-time record of 45 C tied or broken Sunday and Sunday’s record broken Monday. Environment Canada predicts 44 C (111 F) in the Fraser Valley east of Vancouver Sunday and 45 C (113 F) Monday.
How I hope that these model are wrong and the usual suspects on the Right get an opening to laugh. God, I hope I’m wrong!
Three days of all-time record-breaking heat is inconceivable to most Americans. It will not be inconceivable in the Pacific Northwest nor in British Columbia.
Longer-term Summary
The center of the hot dome will migrate northeastward. Environment Canada says that temperatures in north-central Alberta will reach near 40 C while southern Alberta generally stays under 37 C. From there the core of the heat will roughly follow the 58th-60th Parallels with near 100 F at Fort Liard NT earlier in the week, weakening into the mid-30s over northern Saskatchewan and Manitoba, and ending Thursday with 28 C at Arviat, NV (61.1 N) and 31 C at Churchill, MB (58.7 N) Inland areas of NW Ontario and eastern Manitoba (north of 52) will stay warm Friday (32 C), with James Bay and Hudson Bay communities only entering the mid- to upper 20s C.
(Reference: 40 C = 104 F, 38 C = 100 F, 35 C = 95 F, 32 C = 90 F, 30 C = 36 F, 27 C = 80 F)