MOUNTAIN WEATHER FORECAST

Stevens Pass Mountain Weather Forecast

Day and Time: 0630 Monday 1/7/2019

Current Observations:

24hr Precipitation:  .39 swe, 7”snow

Temperature profile: 26 base, 22 ridges

Pass level winds:- 5-10 W

Barometer: 1004mb’s and rising

Sky: OC

Radar: Scattered snow showers with a weak convergence zone formed

The Forecast:  Diminishing snow showers with some partial clearing can be expected later today.  More snow arrives tomorrow afternoon with rising freezing levels heading into Wednesday.

Long Range: Mixed rain and snow below 4500’ can be expected on Wednesday and Thursday with Friday trending dry.

  

The Science: A dirty ridge, out in front of a developing low pressure system, is the mechanism for tonight’s brief dry period. 

A large low pressure system, tracking toward the Pacific coast, will bring the next round of moisture and rising freezing levels to the Cascades tomorrow.   With the cold air mass in place, snow will be the precipitation type tomorrow and likely into early Wednesday morning.  The southerly flow aloft will strengthen and eventually erode the cold air trapped in the eastern basin as the week progresses.

Confidence in the next 24 hours is good with lowering confidence in the mixed snow/rain event on Wednesday/Thursday.    

Values from 4am today through

 4am tomorrow.

Precipitation: Today 24hr water: >.25 snow: 1-2 Tomorrow’s 24hr water: .5  snow: 4-6 Trend and Timing: Diminishing snow showers today.  A new round of snow arrives around noon tomorrow.

Temperature: Low: 14    High: 26 Freezing level: 2500’- 1500’ Trend and Timing:    Freezing levels will fall below 1000’ tonight with cold east flow influence.  Temperatures begin to slowly rise tomorrow.

Winds Base: 5-10 W shifting E Ridge Top: 5-10 W shifting E Trend and Timing: East flow will develop tonight and strengthen. Watch for gusty down slope winds tomorrow.

Glossary 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.