Update on Potential Localized Snow and Chance of Thunderstorms

No FastCast tonight...keep reading below for an update on the potential localized lowland snow and a chance of thunderstorms on Monday.

Here's the overall setup for Monday: Convergence Zone bands and post-frontal showers will combine with a colder airmass to produce localized snow showers and potentially snow pellets. There is also a chance of thunderstorms, mainly in the afternoon. Any afternoon showers could produce an isolated lightning strike.

Let's start with the snow forecast from the NAM high-resolution model. This goes through early Tuesday morning.

This forecast shows some Convergence Zone bands producing 0.25-0.5" of snow from Lakewood to Puyallup, from North Seattle east to Kirkland, and a more robust area of snow from Everett to Bellingham, with 1-3" possible. I'd expect those higher totals to be confined to higher hills and heavier showers.

As you can sese, the mountains will also receive a huge amount of snow, with 1-2 additional FEET possible at the passes.

Next, let's take a look at the HRRR forecast, which shows more snow than the NAM, representing a colder and somewhat snowier scenario.

This forecast shows areas from Olympia southward getting 1-3" of snow (somewhat possible, not very likely). Areas from Tacoma to Seattle could get 0.25-1" in this forecast, with areas from Shoreline to Marysville getting 1-2", and areas from Marysville northward getting 0.3-1". This forecast likely overdoes snow for the entire region, so I wouldn't expect this to happen, but it is still within the realm of possibility.

Now, let's switch gears and take a look at the thunderstorm potential for Monday afternoon. Below is the HRRR forecast for CAPE (measure of instability in the atmosphere) on Monday afternoon.

This forecast shows CAPE values of 100-375 across the lowlands, which is enough for an isolated lightning strike around the region. The NAM high-res forecast (not shown) has much higher CAPE values, showing that instability will definitely be elevated across the region.

To see if these forecasts are on to something, we can look at the European model forecast for lightning flash density (a forecast of where lightning could strike). The image below is for early Monday afternoon.

This forecast shows a decent lightning potential for the South and Central Sound. Remember, any showers on Monday have the potential for thunder & lightning, plus snow pellets (sometimes incorrectly known as graupel) and even brief snow.

Stay safe out there on Monday (especially in the mountains), and if you are on Twitter/X, feel free to tag me (@The_Weatherman2) and report what kind of weather you're seeing!