FastCast—Wednesday, May 10 to Sunday, May 14:
A rare May heat wave is beginning to build. Highs will increase to the low to mid 70s across the lowlands on Wednesday and Thursday, with mostly sunny conditions on Wednesday and partly sunny conditions from late Wednesday to Friday. Highs on Friday will increase to the upper 70s to low 80s, then will increase even more on Saturday, likely in the upper 70s to mid 80s. Sunday (Mother’s Day) will be quite hot, with lowland highs reaching the mid 80s to low 90s. On all these days, subtract 3-5 (or more) degrees from highs if you’re near the water. Expect lows in the mid to upper 40s through Thursday, then in the low to mid 50s on Friday and Saturday, and finally increasing to the upper 50s to low 60s on Sunday. Hot conditions will likely continue on Monday and Tuesday, but that is a more uncertain forecast due to the potential for monsoon moisture moving north from the Desert Southwest, which may induce a potential for muggier conditions and possible thunderstorms. Remember that local water temperatures are in the upper 30s to mid 40s (rivers & lakes) to upper 40s/low 50s (Puget Sound & Pacific Ocean). This means that water temperatures are 30-50º below air temperatures. Beware of this when recreating in any bodies of water during this heat wave.
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Continue reading the full blog below!
A May heat wave with potential record-breaking temperatures is ahead. Let’s take a look at the forecasts.
First, the GFS forecast for Wednesday’s highs (Thursday will be similar…but add 1-3º).
Expect lowland highs in the mid 60s to mid 70s on Wednesday and Thursday, with coastal highs in the low 60s to low 70s (warmer inland), and highs in Eastern WA in the mid 60s to mid 70s.
Next, the highs for Friday, also from the GFS model.
By Friday, lowland highs will increase to the mid 70s to low 80s, hottest from Seattle southward. The coast will reach the mid 60s to mid 70s, and Eastern WA will reach the mid 70s to low 80s.
As the next GFS graphic shows, highs will increase even more on Saturday to begin Mother’s Day Weekend.
On Saturday, expect lowland highs in the mid 70s to low 80s north of Seattle and in the low to mid 80s south of Seattle. Areas near Portland could reach the upper 80s. Expect the coast to reach the low to mid 70s on the beaches and the low to mid 80s inland. Eastern Washington will reach the upper 70s to mid 80s.
Sunday (Mother’s Day) is currently forecast as the hottest day. We will look at more forecasts for Sunday in future blogs, but below is the GFS forecast.
In the lowlands, expect highs in the upper 70s to mid 80s north of Seattle and in the mid 80s to low 90s south of Seattle and into Portland. The ocean beaches will peak in the upper 70s to mid 80s, and inland coastal communities will reach the upper 80s to low 90s. Since the “thermal trough” that brings the highest heat will be west of the Cascades, Eastern WA will be slightly cooler, in the low to mid 80s.
To end the blog, we will take a look at the consensus between the two main global models, the European and GFS, showing that a massive ridge of high pressure is expected by the weekend.
First, below is the GFS forecast for late Saturday.
Notice the massive ridge of high pressure extending from the Pacific Northwest into Northern Alberta and Saskatchewan. That will allow the “thermal trough” to build along the West Coast, bringing hot conditions from Saturday through early next week.
Let’s compare this with the European model’s forecast, also for late Saturday.
Wow! The European and GFS are nearly identical (somewhat rare these days), with the European also showing a massive ridge stretching from the Pacific Northwest into the Canadian Shield.
Stay tuned for more information in the coming days, as details get refined for the hottest temperatures and as we monitor the potential for monsoon moisture from the Desert Southwest potentially moving in early next week.
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