Note: John Meriwether is out of the country for a bit, so I will issue forecasts as they are pertinent on my days off. I'll send out an update on Tuesday/Wednesday's storm tomorrow evening.
Time and Day: Monday and Tuesday
The Snapshot: Dry Sunday morning with moderate snow moving in Sunday afternoon.
The Science: 5" seems to be the new daily norm. After yesterday's frontal passage Washington is in a relatively cool trough with moderate upper level westerly flow bringing continued light snow showers. As the trough moves east today, westerly flow will continue to bring moist air into the region and support snow showers throughout the day Monday and into the evening. A tapering of precip is indicated for Monday night/Tuesday morning.
The next feature to impact our region is easily visible on satellite:(http://www.atmos.washington.edu/cgi-bin/latest.cgi?fronts-ir)
A triple point low will begin to affect Western Washington Tuesday afternoon. Currently the precip type looks to be snow on Tuesday and Wednesday morning. There is plenty of moisture with this system and light east flow indicated for Stevens Pass on Wednesday morning. The free air freezing levels are in our favor for all of Tuesday and early Wednesday, so Stevens could pick up significant snow accumulation by daylight Wednesday morning. The rub is that there simply isn't much cold air east of the Cascade Crest this time of year. This event could play out a number of ways so confidence is low in the final outcome by Wednesday morning but the best guess is heavy snow Tuesday night and early Wednesday, with a switch to rain around daylight Wednesday morning. Moderate rain continues during the day Wednesday before the trailing cold front arrives and drops snow levels again.
The Long Range: After a switch back to snow Wednesday night/Thursday morning, Stevens should see light snow accumulations Thursday. High pressure builds into the PNW on Friday, bringing a sunny and warm day. Another low pressure trough moves into the region over the weekend for light snow/rain.
24hr Precipitation ending at 4am:
Today 24hr water = .25-.5 snow = 2-4"
Tomorrow’s 24hr water = 1.0 snow = 8-12+"
Trend and Timing:
Light snow showers will continue Monday, with a decrease overnight and Tuesday morning. Moderate snow begins again Tuesday midday, becoming heavy overnight and early Wednesday morning. A switch to rain is indicated mid-morning Wednesday.
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24hr temperature ending at 4am:
Low: 28 High: 35
Freezing level: 4,000'- 6,000'
Trend and Timing:
Snow levels should remain at or just above Pass level through Tuesday night before spiking to 6,000' or so Wednesday morning.
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24hr Winds (mph) ending at 4am:
Base: W 5-15
Ridge Top: WSW 10-20, then 20-30 Tuesday night
Trend and Timing:
Light to moderate westerly winds Monday and Tuesday, becoming stronger Tuesday afternoon and evening. Easterly Pass level flow is indicated Tuesday night and Wednesday morning as the warm front approaches.
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