MOUNTAIN WEATHER FORECAST

Stevens Pass Mountain Weather Forecast

Day and Time:  Wednesday 0700

Current Observations:

24hr Precipitation: Raining.  1.95swe, 11” of snow  

Temperature profile: 36 base, 32 base

Pass level winds: moderate,  westerly

Barometer: 1011mbs and holding

Sky: OC

Radar:  rain below 5000’ falling in the mountains with the approaching cold front moving into Puget Sound.  

The Forecast:  The precipitation will begin to diminish this afternoon with gradual cooling.  Light snow showers will linger into tomorrow with a drying trend beginning.  

Long Range:  A stretch of dry, mostly clear and relatively warm weather begins on Friday and will likely last into early next week.  Temperatures, with the aid of the sun, could hit 40f over the weekend.  

  

The Science:  The atmosphere will remain unstable with convergence conditions persisting through the day.  The approaching cold front is expected to pass east of the Cascades in a few hours.  Temperatures will fall a few degrees, the rain will hopefully shift to snow and begin to diminish with the passing of the front.  

High pressure builds over the PNW tomorrow setting up a prolonged dry, partly cloudy and relatively warm stretch of weather.  

Confidence is good.

Values from 4am today through

 4am tomorrow.

Precipitation: Today 24hr water: .25-.5  snow: 2-4 Tomorrow’s 24hr water: .10  snow: trace Trend and Timing: Rain shifts to snow showers today and then tapers off overnight.

Temperature: Low: 30    High: 36 Freezing level: +-4000’ Trend and Timing:    Freezing levels will slowly fall to 4000’ or slightly lower over the next 24hrs.

Winds Base: 5-10 W Ridge Top:  5-15+ W Trend and Timing: Winds will be gusty at times and begin to diminish this afternoon.

Glossary of PNW Weather Terms: 

Storm Water Equivalent (SWE)…. how much water is in the snow or rain

Orographic lift…. an airmass that is lifted as it moves up and over higher terrain. This promotes cloud development, and enhances precipitation.

Dirty Ridge…. a weak, unorganized high pressure ridge.

Advection…. the transfer of heat by the flow of fluid.  For the PNW, this is usually from warm moist air entering the region from the south.

Flow…. wind direction.  In meteorology, the wind direction is always noted where the wind is coming from.   East flow is wind coming from the east; SW is from the south west…

The Inter-mountain West….. the region between the Rock Mountains and the Cascade Mountain ranges.  Mainly Idaho and Western Montana.

Puget Sound Convergence Zone….. This is formed when large scale westerly flow splits around the Olympic Mountains and then converges over Puget Sound.  The flow then accelerates up the river valley’s enhancing the orographic effect at the Passes. 

Occluded Front…..The boundary that separates the cold air mass behind a cold front and the warm air associated with a warm front. When the cold front overtakes the warm front it occludes.