MOUNTAIN WEATHER FORECAST

Stevens Pass Mountain Weather Forecast

Date: Thursday, December 12, 2019

Current Observations:

24hr Precipitation:     6” / .55” SWE

Temperature profile:  32 base / 30 mid-mtn

Pass level winds:   Westerly, moderate with gusts

Barometer:     1009 steady

Sky:     Obscured / Snowing

Radar:  Widespread snow and rain across the PNW

The Forecast: Windy with fast moving, intense snow showers today and cooling temperatures. Further cooling and continued brief, but intense snow showers Friday.

  

The Science: This morning finds the PNW in a classic winter storm scenario. A deep low in the Gulf of Alaska in conjunction with strong zonal 500mb flow and the jet stream positioned directly over Washington will drive a series of cold fronts and orographic snow showers through our area in the next 48 hours. As moist, mid-level air is forced against the topography, the upper level jet will allow for divergence and enhanced lifting. All these mechanisms promote increased precipitation. An embedded cold front will move thru Washington mid-morning, with upper level flow becoming direct westerly behind it, forming several convergence zones throughout Western Washington.

          The fast moving nature of the upper airmass will make exact timing and precipitation amounts a little tricky to pin down. Over the course of the past few days the higher resolution models have showed convergence zones popping up all over the place, some centered over Stevens Pass and others to our north and south. This pattern will be in place through Friday afternoon when a high pressure ridge begins to build and shift upper level flow to northwesterly.

Long Range:  NW flow should bring continued light snow showers over the weekend at much cooler temperatures. A high pressure ridge building in the Pacific will likely dominate the pattern for the beginning of next week bringing dry conditions.

Confidence: Good in the overall scenario, fair in exact snowfall amounts for today and tomorrow.

Values from 4am today through 4am tomorrow.

Precipitation: Today 24hr water: .75-1.0  snow: 8-12” Tomorrow’s 24hr water: .5  snow: 4-8” Trend and Timing: Snow showers ramping up Thursday afternoon, becoming moderate to heavy.

Temperature: Low: 28   High: 32 Freezing level: 4000’ lowering to 3000’ Trend and Timing:    Cooling during the day and overnight.

Winds Base: W 10-15 Ridge Top: WSW 20-30 Trend and Timing: Winds increasing and becoming gusty this afternoon, with sporadic bursts throughout the day. Dan