FastCast--Thursday, Nov. 2 to Monday, Nov. 6:
The atmospheric river has arrived in Western Washington, and will spread rain across the state over the next day. In the lowlands, expect 1-2" of rain, with less in the traditional rain shadow areas NE of the Olympic Peninsula. Mountains and coastal areas will receive more rain (2-3" at the coast, up to 5" in the mountains). Keep in mind that the lowlands will be receiving a high amount of rain in a short amount of time (12-18 hours), so ponding, standing water, and urban flooding are possible. Be aware of clogged storm drains as well. Expect rain to be heaviest from late Wednesday night through early Thursday morning, tapering off through the day Thursday. Warm southerly flow will bring much warmer temperatures, with highs from Thursday to Saturday in the upper 50s to low 60s. From Sunday to Monday, expect temperatures in the mid 50s. Winds will pick up on Thursday morning, likely gusting 25-35 mph across the lowlands, but stronger on Whidbey Island and near the water. Expect a break in the weather from Thursday afternoon through most of Friday. Then, the next storm (and potential atmospheric river) will arrive late Friday, continuing through late Saturday, before the next storm arrives from late Saturday through Monday. Details on those storms are uncertain, so stay tuned for more information.
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Continue reading the full blog below!
An atmospheric river is currently impacting Washington, with heavy rain expected through Thursday for most of the region. Let's take a look at the forecast!
First, the European model forecast for total rain through Friday morning.
This forecast shows 1-2" in the lowlands (most from Seattle to Tacoma, in the foothills, and in Whatcom County). Additionally, this forecast shows 1.5-3" on the coast and from Shelton westward, with 0.7-1.3" in the Willamette Valley and 3-5" in the Olympics and Cascades. Eastern Washington gets widespread rain with this forecast, showing 0.5-0.8" for Ellensburg and Yakima, 0.3-0.6" for Moses Lake and the Tri Cities, and 0.6-1.2" for Spokane and Pullman.
Let's compare this to the GFS (American) model, seen below (also showing total rain through Friday).
This forecast has a few differences. It also shows 1-2" for the lowlands, with the most from Seattle to Olympia. Areas from Seattle north will get 0.8-1.3" in this forecast, with a rain shadow over the NE Olympic Peninsula and Whidbey/Camano Islands. Eastern Washington gets less rain overall in this forecast, with the Spokane and Pullman areas getting the most, around 0.4-0.6". The Cascades and Olympics get 2-4", with 1-3" on the coast.
Now, let's take a look at the high-resolution NAM forecast, showing total rain through Friday morning.
The NAM shows 0.9-2" for the lowlands, with the most between Seattle and Olympia and in the foothills. This forecast also shows 1.5-3.5" on the coast, 5-10" in the mountains, and 0.3-1.3" in Eastern Washington, most near the Idaho border. This forecast also has a small but very pronounced rain shadow near Port Townsend and Sequim.
Finally, the UW WRF high-resolution forecast for rain through Friday morning, specifically zoomed in on Western Washington.
This forecast shows 0.75-1.25" of rain from Seattle to Olympia, with up to 1.25" in the foothills, 1-2" on the coast, and 2-5" in the mountains. Areas from Seattle northward get 0.3-1.25" in this forecast, most along the I-5 corridor from Arlington to the Canadian border.
Forecasts have a relative consensus on the metro area getting 0.75-2" of rain from late Wednesday night through midday Thursday. Ponding, standing water, and urban flooding are possible. Hydroplaning and low visibility will be a concern, so drive prepared!
There is also a potential (but somewhat unlikely) for winds gusting up to 40 mph, especially from Tacoma south and from Everett north, mainly Thursday morning, adding to potential storm impacts. Coastal areas, especially from Ocean Shores southward, will gust up to 45-50 mph, strongest early Thursday morning on the immediate coastline.
We will round out this blog by taking a look at the warming temperatures. Below is the European model forecast for Thursday's highs.
On Thursday, expect lowland highs increasing to the upper 50s to low 60s, with coastal highs in the mid 50s, Willamette Valley highs in the low to mid 60s, and mountain highs in the mid to upper 40s. Eastern Washington will reach the mid 40s to low 50s, except the upper 50s to low 60s for the lower Columbia Basin.
Next, Friday's highs, also from the European model.
On Friday, temperatures will warm in the lowlands, with highs reaching the low 60s for most locations, with some areas, mainly in Whatcom County and on the coast, remaining in the upper 50s. The Willamette Valley will reach the low to mid 60s. Eastern Washington will reach the mid 50s to low 60s south of I-90, and will remain in the mid 40s to low 50s north of I-90.
Finally, the highs for Saturday, seen below.
Saturday will be balmy across the region, with lowland and Willamette Valley highs reaching the low to mid 60s (warmest in the foothills). The coast will remain in the upper 50s, but Eastern Washington will begin warming up more, with most areas except Wenatchee and the North Cascades warming to the mid 50s to mid 60s, warmest around the Tri Cities and Walla Walla.
Finally, a quick preview of what's ahead for the metro area. Below is the European EPS ensemble forecast for 24-hour precipitation in Seattle through the next 2 weeks.
Notice the current system (red outline) and the upcoming Saturday system (purple outline). For the current system, nearly every ensemble member shows 1-2" of rain, but there is less agreement amongst the ensemble members for the Saturday system. Forecasts are still coming into agreement on that system and the next system, slated for Sunday/Monday. Regardless, an active period is upon us in the Northwest, so stay tuned for updates!
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