MOUNTAIN WEATHER FORECAST

Stevens Pass Mountain Weather Forecast

Day and Time: Thursday 1/17/2019 0630am

It’s good to see the snow back. 

Current Observations:

24hr Precipitation: Snowing .02swe, 0” of snow

Temperature profile: 28 base, 24 ridge

Pass level winds: light and out of the east

Barometer: dropped to 1001mb’s

Sky: OC

Radar: Light snow falling in the mountains will scatted showers to the west.  

The Forecast: Light snow showers will persist today with moderate to heavy snow and warmer temperatures expected to greet the day tomorrow.   

Long Range:  Snow with a short period of mixed rain can be anticipated on Saturday.  Sunday and Monday will be dry under a clearing trend.   

  

The Science: The cold front, associated with the low pressure cell tracking NE along the NW coast has occluded. This will help stabilize freezing levels around 4000’ over the next 24hrs.  Once the front moves east of the crest late tonight, winds will shift westerly with good orographic snow possible. The Puget Sound Convergence Zone will likely form but may be aimed north of Stevens Pass.

A fast moving triple point frontal system with SW warm air advection will move in early Saturday morning.  A short-lived spike in freezing levels (5000’) with cool air quickly filling in will be the game Saturday mornings.  The precipitation tapers off on Sunday and Monday as another high pressure ridge slides into place.

Confidence is good in the next 24hrs,  fair to poor in the timing and intensity of the warm up Saturday morning.

Values from 4am today through

 4am tomorrow.

Precipitation: Today 24hr water: .5-.75  snow: 6-8 Tomorrow’s 24hr water: .75+  snow: 3-5 base, 5-8 upper mountain Trend and Timing: Snow intensifies late tonight and tapers to intermittent showers after 7am tomorrow.

Temperature: Low:  26   High: 30 Freezing level: 2500’- 4000’ Trend and Timing:    Freezing levels will slowly rise to +-4000’ over the next 24hrs.

Winds Base: 0-10 E shifting W Ridge Top: 5-15 Trend and Timing: East flow will shift WSW after 10pm tonight.

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…

Intermountain West…. the mountain ranges between the Rockies and the Cascades.  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 valleys producing good orographic precipitation at the Passes. 

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