We are now in the driest period of the year in the Pacific Northwest. Below is the daily climatological probability of a trace or more of precipitation in Seattle.
Just amazing: we bottom out from roughly July 5 through August 15th, with the lost few days of July (NOW) the most arid.
Crossing the Cascades to Sunnyside, we find a similar dry period...although the general level is much lower in the arid Columbia Basin.
The reason for this climatological Northwest dry period is clear: the jet stream and storm track are not only weakened in mid-summer, but are also positioned to our north during this period
Furthermore, with cool waters offshore, we don't get many thunderstorms, unlike much of the U.S.
Interestingly, the models are now suggesting that many will experience precipitation during the normally dry period.....let me show you.
Starting with the latest UW WRF model forecast for accumulated precipitation over the next five days, one notes substantial precipitation from northern California into eastern Oregon, with a few showers making it into the southern WA Cascades.
This precipitation pattern has been persistent over the past few weeks, with portions of northern CA and eastern Oregon wetter than normal (see below, green and blue colors).
A number of model runs are showing a significant change in the pattern of the past few weeks with a series an energetic troughs of low pressure pushing south into British Columbia, shifting the rain shield south.
The latest UW extended precipitation total through Monday afternoon (August 4th) shows the moisture. Impressive for this time of the year, with welcome precipitation over the wildfire region east of the Cascade crest.
Puget Sound will be rainshadowed by the Olympics.
The ensemble systems of many forecasts concur with this moist forecast, and the NOAA Climate Prediction Center 6-10 day precipitation forecast is for above-normal precipitation over our region.
Will this rain help to put out the wildfires that are currently burning in the Olympics, the Columbia River Gorge, and the North Cascades?
ReplyDeleteI do wonder if that area of Oregon gets impacted by the southwestern monsoon. The southwest monsoon has to be the weakest monsoon on the planet, but it's the reason why Seattle has drier July/August weather than metro Phoenix. Go a little further north to Las Vegas and the "wet" mid-summer" boon is much less.
ReplyDeleteI'm so used to thinking of Phoenix as always being so dry, that I forget that they actually have much of a rainy season each year. Its hard to believe that our summer weather is often drier than theirs.
DeleteIt seems like there may just be enough precipitation to help with the Bear Gultch fire in the Olympics. It would be great to see some helpful rains fall in the fire on the WA side of Columbia Gorge too. I'm all in for some mid-summer rain
ReplyDeleteI should add that, overall, this July has had very pleasant weather in the Bellingham area and it appears, based on the current forecast, that this month will end up with perfectly normal average temperature (though substantially below normal precipitation) and will also be the coolest July since 2020. Let’s hope that the comparisons with 2020 do not extend to wildfire as I’m sure we all remember that fateful season.
ReplyDeleteI for one haven't forgotten. The fires and smoke that year was downright horrible! For a lot of people, it was the year where the threat of large and destructive wildfires west of the Cascades went from being somewhat distant to very, very real.
DeleteNot sure to what extent the wildfire threat is affected by this, but going through the NWS Seattle NOWData it is striking how anomalously warm the higher elevation stations have been this month compared to those in the lowlands. All of the mountain stations have been well above normal and multiple such stations have average monthly temperatures >4F above normal, while the lowlands have been generally much closer to normal.
ReplyDeleteLooks like lightning storms are likely for later this week and hope Cliff is right about rain with the storms as pre-storm conditions look warm and dry. Will need more than light showers since it has been dry for so long along the Cascade east slopes.
ReplyDeleteThis pattern (SW monsoon pushing in from the South) has been a common one since I was a young man in the 90's windsurfing in the gorge. These pesky South winds would often ruin what otherwise was a good thermal setup across the cascade crest.
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