Major Changes Ahead: Heavy Mountain Snow, Return of Rain

FastCast—Wednesday, Nov. 29 to Saturday, Dec. 2:

One more cold and stagnant day with morning lows in the upper 20s and areas of dense fog and some areas of freezing fog lasting into the afternoon is expected on Wednesday. Highs will only reach the upper 30s to low 40s. However, major changes are afoot. On Thursday, morning lows will reach the low 30s, but fog will lift, temperatures will increase to the low to mid 40s, and rain will arrive. Our stagnant air will clear out, and the lowlands will receive 0.25-0.5” of rain. There will be a brief break in the rain late Thursday, before rain continues on Friday, with another 0.5-1.3” for the lowlands as rain continues through Saturday evening. This storm will bring the first major mountain snow of the season, with the passes likely to receive 18-30”, mainly from Friday to late Saturday. For Friday and Saturday, expect lowland highs in the mid to upper 40s, with lows in the low 40s. Friday will also be breezy across the area, with winds gusting 25-35 mph, strongest near the water.

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Continue reading the full blog below!

Major weather changes are ahead for the Northwest, as the persistent high pressure ridge that has brought an inversion (trapping fog and cold air near the surface) will break up on Thursday. 

However, on Wednesday morning, freezing fog is possible across the lowlands, with morning lows in the upper 20s to low 30s. Fog may persist well into the afternoon in the South Sound as has happened on Monday & Tuesday. Degraded air quality will persist into early Thursday, until onshore winds erode the stagnant air that is in place.

Rain will begin midday Thursday, with a break overnight and then more persistent rain from Friday to Saturday. Mountain snow is most likely from early Friday to late Saturday. 

Let’s start by taking a look at the European model forecast for rain through Saturday night.

Through Saturday night, the European model shows 1-1.5” for the lowlands, with 0.5-0.8” in the rain shadow from Everett to Victoria BC. Areas from Olympia southward to the Willamette Valley will likely receive 1.5-2” of rain, with 1.5-2.5” on the coast. For the mountains below 2,500 feet, expect up to 2” of rain.

Let’s compare the European model rain forecast to the GFS (American) model, seen below also showing rain through Saturday night.

The GFS shows less rain overall, with 0.7-1.3” for the lowlands, a slightly larger rain shadow, extending from Seattle to Bellingham (0.5-0.8” in this area), and totals from Olympia south and on the coast around 1-1.5”. 

Now, let’s shift gears to the first major mountain snow event of the season. Below is the European model forecast for snow through Saturday night.

The European model shows an impressive 18-30” of snow for the passes, mainly from Friday to Saturday. Significant impacts are possible, so stay tuned. Additionally, snow is possible across Eastern Washington from Thursday night into early Saturday. The European model shows 2-4” north of I-90 (up to 6” near Ellensburg and Wenatchee), with 0.5-1.5” for the rest of Eastern WA except the Pullman area, where 3-5” are possible. 

Next, let’s take a look at the GFS forecast for snow, also through Saturday evening, seen below.

The GFS forecast also shows 18-30” for the passes, but has a different forecast for Eastern Washington. This model shows up to 6-8” of snow around Spokane, with 4-6” around the Palouse, but only 1-2” for the rest of Eastern Washington.

We’ll round out this blog by taking a look at the high-resolution UW WRF forecast for rain (Western WA only) through Saturday evening.

The UW forecast shows 0.75-1.5” from Tacoma southward, with 0.5-0.75” from Tacoma northward. The coast gets 1.25-2” in this forecast, with areas from Olympia south getting 1.5-1.75”.

Finally, the UW forecast for snow across Washington through Saturday evening.

The UW forecast also shows 18-30” for the passes, with 4-6” for the Palouse and Spokane area, and 0.5-2.5” for the rest of Eastern WA, except more close to the Cascades. 

The upcoming storms are likely the first of multiple potent storms, with much more active weather possible from the weekend into next week, so stay tuned to the blog for more information!