MOUNTAIN WEATHER FORECAST

Stevens Pass Mountain Weather Forecast

Day and Time: Tuesday 1/8/2019, 0630

Current Observations:

24hr Precipitation:  .14swe, 2”snow

Temperature profile: 22base, 18ridge

Pass level winds: 5-10 E

Barometer: 1019mb’s steady

Sky: high clouds

Radar: the approaching moisture is entering the SW region of the state and tracking NE.

The Forecast:  Snow today with rising temperatures.  The battle between rain and snow begins after midnight tonight and will continue through most of tomorrow.

Long Range: A drying trend begins and Thursday and will likely continue through the weekend.   

  

The Science: A low pressure system with an embedded triple point will track through the PNW today.  Cold air trapped in the eastern basin will provide ample east flow shelter for the warm advection coming along for the ride.  Freezing levels will rise to +4500’ tonight. The winner between the warm air from the SW and the cold east flow will determine how much snow the Pass will receive over the next 24-36hrs.  

Confidence in the precipitation amounts and type is poor to fair.

A high pressure ridge forming over the Intermountain West will begin to divert the moisture stream starting on Thursday.  A split flow pattern will likely provide the PNW with a dry weekend.  Temperatures will be on the mild side for mid January with freezing levels stationed +-4000’ through the weekend.   

Values from 4am today through

 4am tomorrow.

Precipitation: Today 24hr water: .5 -.75  snow: 4-8 Tomorrow’s 24hr water: .75  snow: 2-4 Trend and Timing: Snow arrives mid-morning and is expected to change to mixed rain and snow after midnight.

Temperature: Low: 18    High: 28 Freezing level: 1000’ – 4000’ Trend and Timing:    Freezing levels will slowly rise today peaking near 4000’ around midnight.

Winds Base: 5-10 E Ridge Top:5-15 E Trend and Timing: East flow will strengthen today.  East flow should hold through the night and most of the day 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…