FastCast—Wednesday, Apr. 5 to Sunday, Apr. 9:
Another calm day is ahead on Wednesday, with a chilly morning (low to mid 30s in the lowlands), and a mostly cloudy day. Rain will move in after dark as a weak atmospheric river parallels the Washington and Oregon coasts. Rain will continue through midday Friday, becoming showery from late Thursday night through midday Friday. Expect rain totals in the lowlands of 0.6-1.3”, most from Seattle southward. On the coast and in the Olympics, expect 1-3 inches. The Cascades will also receive 0.8-1.5”, and snow levels will hover at 4,000-5,000 feet. Eastern Washington will also pick up 0.25-0.5” of rain. Another system, essentially a mini atmospheric river, will impact the area from Saturday through Sunday. This system will bring widespread rain to the region, but rainfall amounts and snow levels aren’t certain yet. Through Sunday, expect highs in the low to mid 50s and lows in the low to mid 40s.
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Continue reading the full blog below!
A weak atmospheric river is ahead for the Pacific Northwest, impacting the region from late Wednesday through midday Friday. The UW forecast below shows the integrated water vapor transport (IVT) values at 2 PM Thursday.
This graphic essentially shows the amount of water vapor in the atmosphere. The atmospheric river is clearly visible…the long trail of red paralleling the WA & OR coasts.
How much rain is expected with this atmospheric river? Let’s take a look at the European model’s forecast below, through Friday night.
In general, expect 0.6-1.3” of rain in the lowlands, most from Seattle southward and on the Kitsap Peninsula. The coast and Olympics will receive 1-3”, and the Cascades will receive 0.8-1.5”, with snow levels at 4,000-5,000 feet, likely bringing rain to Snoqualmie Pass and rain/snow mix (or all rain) to Stevens and White Passes.
One note before we take a look at big changes to the extended forecast. Below is the forecast for low temperatures on Wednesday morning, per the European model.
Expect chilly lows in the low to mid 30s across the lowlands, with outlying areas dropping into the upper 20s. Eastern Washington will drop into the low to mid 20s, except in the upper 20s to mid 30s in the Columbia Basin.
Now…big changes in the extended forecast. If you remember my previous blog, I talked about the NWS Climate Prediction Center (CPC) temperature outlook for April 8-12. That outlook showed a significant warmup ahead for the Northwest. This was due to predictions of a large high pressure ridge setting up over the Northwest, which would deflect weather systems away and bring warmer weather.
However, in the past few days, forecasts have significantly changed, pushing the high pressure ridge further east toward the Rockies and beyond. This has cooled and dampened the forecasts considerably for the Northwest, since we’re now wide open for systems to arrive.
Let’s take a look at the CPC temperature outlook for April 10-14.
This is a huge change from the previous outlook. Now, we’re expecting a 40-70% probability of below average temperatures, a total pendulum shift from the previous blog. You can see the area of above average temperatures on the edge of this map, mainly centered over the Great Plains and parts of the Southern Rockies.
Now for the CPC precipitation outlook for April 10-14. As you’d expect, chillier temperatures will bring some more rain.
This outlook puts Washington in the bullseye of above average precipitation through mid-April, with a 40-60% probability of precipitation being above average. While dismal, this is actually good news, since the snowpack has been below normal for the past few months. With a drier summer ahead, we need all the snowpack possible to help suppress wildfires. Cooler and wetter conditions will help with snowpack and solidify our already strong reservoir capacity.
Stay tuned as active weather continues!
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