MOUNTAIN WEATHER FORECAST

Stevens Pass Mountain Weather Forecast

Tuesday, December 17, 2019, 0730

Current Observations:

24hr Precipitation:      .02swe, 0’ of snow

Temperature profile:    20 base, 30 ridge

Pass level winds:            Light east

Barometer:                   1020mb’s and falling

Sky:                               Pass level fog and mid-level clouds

Radar:    Moisture tracking north into southwestern British Columbia with the majority of the state dry. There are light flurries falling out of the inversion layer.

The Forecast:  Mostly dry today with a few snow flurries possible.   Snow arrives tomorrow morning with heavy precipitation expected Thursday night through Saturday.   See storm details below

Long Range: The heavy precipitation continues through Saturday with Sunday and Monday trending dry.    

Storm totals from 4am tomorrow through 4pm Friday.  +2”swe,  12-15” of snow.

  

The Science:  There is a steep 10 degree temperature inversion this morning with west side freezing level around 4500’.  Cool air trapped in the eastern basin is providing good east flow insolation for Stevens Pass.  The atmosphere will remain dry through early tomorrow morning.

The incoming storm:

A long frontal boundary stretching from Southern Alaska to Southern California will drift east/northeast over the next 24hrs.  Complexities start with a cut off low developing from the Gulf of Alaska parent low.  There is a ton of moisture associated with this storm with +3” of water likely by the end of Saturday.

The battle between the cool air to the east and the warm air streaming in from the southwest will begin late Thursday night.   Freezing levels over the southern Cascades could hit 8000’ with the freezing levels in the north Cascades around 3500’-4000’.  Stevens Pass is right in between with uncertainties in the models.

Another cut-off low is expected to drive in on Saturday with more rain vs snow reindeer games.   Stay tuned as those details become more evident.     

Confidence:  Good - short term.  Timing and temperatures are still very much in question for Friday and Saturday.

Values from 4am today through 4am tomorrow.

Precipitation: Today 24hr water: lt.10 snow: trace Tomorrow’s 24hr water: .5-.75  snow: 6-8” Trend and Timing: Snow arrives after 4am tomorrow morning.   Snow tapers off around 10pm tomorrow night.

Temperature: Low:  22  High:  26 base,  32 ridge Freezing level: +-3500’ Trend and Timing:   Freezing levels will hover around 3500’ with the aid of east flow.

Winds Base: 0-10 E Ridge Top: 5-10 SES Trend and Timing: Pass level east flow will hold until tomorrow afternoon with westerly flow taking over.