MOUNTAIN WEATHER FORECAST

Stevens Pass Mountain Weather Forecast

Day and Time: 10/7/19

Current Observations:

24hr Precipitation: .19” of rain        

Temperature profile:  47base  

Pass level winds:           

Barometer: 1014mbs             

Sky:  overcast               

Radar:  Heavy showers moving through the Puget Sound region.

The Forecast:  Moderate rain showers shifting to snow showers this evening.  Snow showers can be expected for most of the day tomorrow. 2-4” of snow will be possible by the end of the day tomorrow.  

Long Range:  The second half of the week will be mostly dry and sunny with freezing levels hovering around 4000’.  Warmer and dry for the weekend.

  

The Science: A cold front is approaching the mountains with moderate rain showers out ahead of it.  Once the front passes west of the crest this afternoon, temperatures will fall with the rain shifting to intermittent snow showers.   As the low pressure system slide SE, it will draw in cold air from the interior mountains of Canada.   Freezing level will fall below pass level tonight and possible hit 2000’ by early Wednesday morning.   

Values from 4am today through

 4am tomorrow.

Precipitation: Today 24hr water: .5-.75 snow: 1-2 Tomorrow’s 24hr water: .25-.5  snow: 1-2 Trend and Timing: Rain turning to snow late tonight with precipitation tapering off tomorrow night.

Temperature: Low: 26  High: 48 Freezing level: 5000’ – 3000’ Trend and Timing:    Temperatures will begin to fall this afternoon and bottom out early Wednesday morning.

Winds Base: 5-10 W Ridge Top: 5-10 Trend and Timing: Gusty winds will continue through the night with winds shifting northerly tomorrow.

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.

High/Low Pressure…. High pressure is associated with sinking air that rotates clockwise. High pressure often results in dry and clear weather.  Low pressure is rising air that rotates counter clockwise and results in condensation, cloud formation and precipitation.