MOUNTAIN WEATHER FORECAST

Stevens Pass Mountain Weather Forecast

Day and Time:  Friday 1000am

Current Observations:

24hr Precipitation:  .39swe, 7” of snow

Temperature profile:  31base, 27 ridge

Pass level winds: Light westerly

Barometer: 1016mbs

Sky: OC

Radar:  There are some remnant showers left falling in the mountains with the next frontal boundary moving up the Oregon coast.

The Forecast:  There will be another round of moderate snow tonight with a short lived spike in temperatures during the early morning hours.   Snow showers will taper off through the day with rest of the extended weekend mostly dry.

Long Range:  Martin Luther King Day will partly cloudy and dry.  A system pushes in on Tuesday/Wednesday for a chance of measurable snow.   

  

The Science:  A fast moving warm front, currently off of the Southern Oregon Coast, will bring the next round of moisture to the Cascades Mountains tonight.  There will be a short lived spike in freezing levels with that passing of the front.  This is timing out to be sometime between 10pm tonight and 7am tomorrow. 

Cooler upper level NW flow will fill in tomorrow.   The atmosphere will slowly stabilize through the day with snow showers diminishing.   A high pressure ridge moves into place on Sunday for a few days of dry and partly cloudy weather.   

Confidence is good.

Values from 4am today through

 4am tomorrow.

Precipitation: Today 24hr water: .5-.75  snow: 1-3 base, 3-5 upper Tomorrow’s 24hr water: .25  snow: 1-2 Trend and Timing: Wet snow will begin after 4pm with some rain mix possible around midnight.  The precipitation tapers off through the day tomorrow.

Temperature: Low: 30    High: 36 Freezing level: 4000’ -5000’-4000’ Trend and Timing:    Freezing levels will hover around 4000’ today, spike up to 5000’ after midnight and then fall back below 4000’ through the day tomorrow.

Winds Base: 0-5 W shifting E Ridge Top: 5-10 W shifting E Trend and Timing: Winds will shift easterly tonight and the back to westerly early tomorrow morning.  Gusty post frontal winds will be possible.

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…

Inter Mountain West…. The region between the Rocky Mountain 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.