Monday Night Weather Update

No FastCast tonight...keep reading below for an update on lowland and mountain snow, Tuesday morning low temperatures, and the incoming heavy rain for the lowlands.

Monday was quite active across the region, mainly from Tacoma northward. Many areas received snow pellets, some areas received impactful snow pellet/hail accumulations, and the mountains received more snow. Snoqualmie Pass recorded 13" of snow today due to persistent Convergence Zone banding.

A break in precipitation is expected on Tuesday morning (some Convergence Zone bands in the North Sound will linger into early Tuesday morning), before the next system spreads rain and mountain snow into the area starting Tuesday afternoon (morning on the coast). That's where we pick up the forecast...

Let's start with the NAM high-resolution forecast, showing total snow through Wednesday evening.

This forecast highlights the potential ongoing Convergence Zone activity, showing that there's a chance of snow from Seattle/Bellevue north and east. I wouldn't believe these accumulations for the lowlands (as they are likely overdone), but that being said, you can't rule out 0.5-1" for some isolated areas under heavy snow banding.

For the mountains, expect an additional 18-30" of snow, mainly falling late Monday night through early Tuesday morning and from midday Tuesday onward, picking up in intensity through the evening. This will likely cause difficult road conditions on the passes, so be prepared!

Next, let's compare that to the HRRR high-resolution forecast, seen below.

This forecast indicates that potential Convergence Zone activity will be further south, but still very light, with isolated higher accumulations around Lynnwood and Redmond. This just represents another potential scenario for where precipitation bands set up.

In the mountains, this forecast agrees with the NAM, also showing 18-30" of new snow at the passes.

One important note for mountain snow is that from Wednesday morning to late Wednesday evening, precipitation will likely change to rain. This is most likely for Snoqualmie Pass and potentially on White Pass. Stevens Pass will most likely stay all snow on Wednesday. Precipitation will change back to heavy snow by Wednesday night, likely continuing into Thursday.

Now, let's take a look at the NWS NBM forecast for low temperatures on Tuesday morning.

Expect lows in the lowlands to reach the upper 20s to low 30s, with the coast only dropping to the mid 30s. Eastern Washington will drop into the low to mid 20s, with the lower Columbia Basin remaining in the upper 20s to low 30s. Any areas that saw precipitation on Monday have the potential for icy spots on roads on Tuesday morning, especially if frozen precipitation covered roads at any time. Be aware of this on Tuesday morning!

Finally, while a lot of the talk has been on snow lately, the lowlands are going to receive quite the rain event over the next couple days as systems bring significant rain from Tuesday afternoon to Thursday. Below is the European model forecast for total rain through Thursday evening.

In the lowlands, expect 1.75-2.5", most from Seattle southward, with a rain shadow bringing 1.25-1.75" from Everett to Bellingham. The coast will be quite sodden, with 3-4" of rain expected. 

We will cover the upcoming storms more in Tuesday night's blog, so stay tuned!