7:30 ABS January 1, 2020

Happy New Year!

STORM UPDATE:

Stevens Pass Mountain Weather Forecast

Storm Update Tuesday, December 31, 2019, 1230

Current Observations:

24hr Precipitation:      .5swe, 1 snow

Temperature profile:     33 base, 32 ridge

Pass level winds:            Light westerly,  becoming gusty on the upper mountain

Barometer:                    1011mb’s and falling

Sky:                              OC and raining

Radar:         Plenty of moisture heading into the mountains with freezing levels at +-4700’

The Forecast:   No significant changes to this morning’s forecast.

Storm details:

Storm water totals: 1200 today through 0400am tomorrow = +1.75” SWE,  0” of snow below 4500’ with 1-3 on upper mountain.

Snow totals 4am tomorrow through  4am Thursday = 10”-14”

Freezing levels peak @ 6500’ this afternoon/evening. Freezing levels fall below 5000’ by 4am tomorrow morning with freezing level falling below 4000’ by mid-morning or so.

Winds:  5000’ WSW winds will begin to increase this afternoon.  40+ winds will be possible through the night.

MOUNTAIN WEATHER FORECAST

Stevens Pass Mountain Weather Forecast

Wednesday, 12/31/19, 0730

Current Observations:

24hr Precipitation:      .15 SWE, 1” of snow

Temperature profile:    31 base, 30 ridge

Pass level winds:            light, westerly

Barometer:                   1014mb’s  and falling

Sky:                              OC and snowing

Radar:           Heavy moisture entering Puget Sound and tracking E

The Forecast:  Heavy rain today then turning back to snow tomorrow.  Winds will also crank up this afternoon with ridge top gust +40pmh possible.  Heavy mixed rain and snow turning to snow can be anticipated tomorrow.

Long Range. A similar event is taking shape for the start of the New Year.  Snow on Thursday changing to rain Friday back to snow Saturday.     

  

The Science:  A strong warm front with a long fetch of moisture will drive into the PNW today.  Warm air advection has begun to stream in in from the SW with the leading edge of the approaching warm front entering Puget Sound.  Freezing levels top out above 6000’ this afternoon and then slowly fall through the night. 

The big question is when the rain will turn back to snow and how much snow accumulation we will get tomorrow.  Snow totals tomorrow could exceed 15”.  There will likely be convergence zone activity with and trough wave tomorrow which will aid in orographic snowfall at Stevens Pass. 

There will be a short break Thursday morning with the next system entering the scene Thursday afternoon.   Freezing levels once again rise to +5000’ on Friday with moderate to heavy rain likely.   

Long range models have a strong cold front with cool unstable NW flow arriving over the weekend with measurable snow heading into the first full week of 2020.

Confidence:  Fair

Values from 4am today through 4am tomorrow.

Precipitation: Today 24hr water: 1-2 snow: 1-3    Tomorrow’s 24hr water: 1.5   snow:  10-15 Trend and Timing: Heavy rain today.  Rain switches back to snow tomorrow with good accumulation likely.

Temperature: Low: 31  High: 38 Freezing level: 4000’ – 6000’ – 4500’ Trend and Timing:    Freezing levels will peak around 6000’ this afternoon and then fall through the night.

Winds Base: 5-15 W Ridge Top:  10-20 W with gust +40 Trend and Timing: A high wind warning will go into affect this afternoon with sustained 40+mph winds at and above 5000’.

7:30 ABS Tuesday Dec 31

ABS YES

MOUNTAIN WEATHER FORECAST

Stevens Pass Mountain Weather Forecast

Date: Monday, December 30, 2019

Current Observations:

24hr Precipitation: 0

Temperature profile: 22 base / 31 mid mtn

Pass level winds: Variable, light

Barometer: 1020 steady

Sky:  Partly cloudy, light snow flurries

Radar: There’s a band of light rain in the northern interior, and spotty snow flurries along the crest.

The Forecast: Increasing clouds with a chance of flurries today, stormy with moderate snow then rain/snow mix Tuesday.

The Science: A weak warm front is riding over the top of an east-west oriented high pressure ridge this morning, bringing light rain to the Puget Sound area and isolated snow flurries in the Cascades. The main affect at Stevens Pass will be increasing upper cloud cover and the end of the inversion conditions we’ve had the past few days. A more uniform temperature profile should set up as the Pass level winds have already switched to westerly.

Tonight the ridge should flatten out as a westerly jet begins to take aim at the PNW. The first in a series of vigorous storms will move in Tuesday morning. Freezing levels are favorable for snow to start the event, and moderate accumulations can be expected during the day tomorrow. A switch to rain looks likely mid-afternoon as the warm sector arrives and pushes freezing levels above 5,000’. The trailing cold front should sweep through overnight on Tuesday, dropping freezing levels below pass level again with continued precip (snow).  

Long Range: Light to moderate snow expected Wednesday with convergence zones popping up, making for varying snowfall amounts. Another, colder storm arrives Thursday with favorable snow accumulations for Stevens Pass. Active weather continues through the weekend with lowering freezing levels.

Confidence: Poor starting Tuesday morning for exact snowfall amounts and timing of precipitation-type changes. 

Values from 4am today through 4am tomorrow.

Precipitation: Today 24hr water: .10 snow: Trace-2” Tomorrow’s 24hr water: 1-1.5”  snow: 6-8” Trend and Timing: Mostly dry Monday with precipitation beginning as snow Tuesday morning, switching to rain in the afternoon, and back to snow early Wednesday morning.

Temperature: Low: 21   High: 33 Freezing level: 4000’ Trend and Timing:    As the inversion scours out this morning, the temp profile should become more uniform, steady temperatures thru Tuesday morning.

Winds Base: West 5-10 Ridge Top: WSW 10-15 Trend and Timing: Light winds increasing to moderate Monday evening.

7:30 Start No ABS Monday December 30th

MOUNTAIN WEATHER FORECAST

Stevens Pass Mountain Weather Forecast

Date: Sunday, December 29, 2019

Current Observations:

24hr Precipitation: 0”

Temperature profile: 23 base / 31 mid mtn

Pass level winds:  Light easterly

Barometer:  Steady at 1016

Sky:  Foggy / overcast

Radar:  Light showers across the Olympic Peninsula and South Sound

The Forecast: Foggy and cold with inversion conditions in base area, partly cloudy and warmer mid and upper mountain.

The Science: A slow moving, weak low pressure system off the Washington coast is pushing up against higher pressure inland this morning and spreading light rain to the Olympic Peninsula. Little more than high clouds will reach the Central Cascades. The pressure gradient is driving east flow thru the mountain passes, creating surface inversions and locally cold temperatures and fog. As the low pressure sinks south and dissipates, a positively tilted high pressure ridge will lean over the PNW for Monday, bringing another dry day and mild temperatures aloft.

Long Range: A significant pattern shift is in store starting New Year’s Eve as a strong jet begins to drive several storms into our region. Freezing levels start near/above Pass level but lower throughout the second half of the week. Details to come.

Confidence:

Values from 4am today through 4am tomorrow.

Precipitation: Today 24hr water: 0 snow: 0 Tomorrow’s 24hr water: <.10  snow: trace Trend and Timing: Dry today and daylight hours Monday, chance of light snow early Tuesday morning.

Temperature: Low: 23   High: 35 Freezing level: 5,000’ / surface at Pass level Trend and Timing:    Free air freezing levels will rise today, east flow will keep inversion conditions and below freezing temperatures on the lower half of the mountain.

Winds Base: E 5-15 Ridge Top: E 5-10 Trend and Timing: East flow thru the Pass will continue thru Monday morning.

7:30 Start No ABS Sunday the 29th

MOUNTAIN WEATHER FORECAST

Stevens Pass Mountain Weather Forecast

Date: Saturday, December 28, 2019

Current Observations:

24hr Precipitation: .15” SWE / 2” snow

Temperature profile: 27 base / 26 mid mtn

Pass level winds: Light westerly

Barometer: 1018 steady

Sky: Overcast

Radar: Light, spotty showers near the crest

The Forecast: Partly cloudy with a snowflake or two possible today. Warmer temps and partly cloudy Sunday.

Long Range:  The weak ridge remains in place Sunday and Monday, allowing for mild days with a few sun breaks. The next chance for snow arrives Tuesday/Wednesday, with a pattern shift looking possible for the end of the week. Stay tuned.

  

The Science: A weak low pressure center will flop onshore today, becoming cutoff from the main upper level flow and basically shearing apart. It will mostly have the effect of bringing a warmer airmass into our area, rising freezing levels and surface temperatures. East flow should develop this afternoon, bringing potential inversion conditions to the mountain passes.

A very positively tilted (ridge axis oriented more west-east) upper level high will move in on Sunday. This configuration of ridge will often allow clouds and light moisture to stream over the top of it and is referred to as a “dirty” ridge. Thus, not expecting full sunshine on Sunday.

Confidence: Good

Values from 4am today through 4am tomorrow.

Precipitation: Today 24hr water: .10  snow: Trace Tomorrow’s 24hr water: 0  snow: 0 Trend and Timing: Light snow flurries possible Saturday, no precipitation expected Sunday.

Temperature: Low: 26   High: 32 Freezing level: 3500-4000 Trend and Timing:    Warming aloft thru Sunday, surface temperatures may stay lower due to east flow influence thru the pass.

Winds Base: Light and variable Ridge Top: W 10-15, then ENE 5-10 Trend and Timing: Winds shifting easterly Saturday afternoon and overnight.

7:30 Start Sat Dec 28th no ABS

Stevens Pass Mountain Weather Forecast

Friday, December 27, 2019, 0730

Current Observations

24hr Precipitation:        .05 SWE,  2’”

Temperature profile:      23 base,  23 ridge

Pass level winds:              Lights, westerly

Barometer:                    1013mb’s and holding

Sky:                            OC and snowing

Radar:           Convergence snow showers in the I-90 corridor and Hwy 2 with scattered showers to the west.

The Forecast:  Snow this morning shifting to intermittent showers tonight.  Mostly dry with a few left over flurries tomorrow.   A repeat performance with another few inches of snow will be possible on Sunday.  

Long Range. Next week starts out warm and dry with more active weather heading into the New Year.   

  

The Science:   Westerly flow with a weak convergence zone effect has kick-in this morning with light snow falling.   A high pressure ridge will drift into place overnight producing a mostly dry day with patchy clouds tomorrow.

A low pressure system with an embedded warm front will bring another round of moisture on Sunday with rising freezing levels.  Next week will start out dry with temperatures above freezing. 

 Models diverge with their take on what may or may not happen next week – but, safe to say that we will be in active weather pattern with systems passing through every over other day or so.  Temperatures are on the uncomfortably warm side of things so we will have to see how the freezing levels play out through the week.      

Confidence:  Good to fair

Values from 4am today through 4am tomorrow.

Precipitation: Today 24hr water: lt. 25  snow: 1-3    Tomorrow’s 24hr water: .10   snow: trace Trend and Timing: Snow shifts to shower this afternoon and tapers off overnight.

Temperature: Low: 23    High:  26 Freezing level: 1500’-3000’ Trend and Timing:    Gradual warming will occur over the next 24-36hrs.

Winds Base: 0-10 W Ridge Top: 5-10 W     Trend and Timing: Winds will be light and westerly today. Surface flow shifts back to easterly tomorrow morning.

7:30 Start Fri Dec 27th no ABS

MOUNTAIN WEATHER FORECAST

Stevens Pass Mountain Weather Forecast

Thursday, December 26, 2019, 0730

Current Observations:

24hr Precipitation:      0

Temperature profile:   17 bas, 23 ridge

Pass level winds:          light, easterly

Barometer:                 1016mbs’ and holding

Sky:                              broken clouds

Radar:                Dry conditions in the mountains

The Forecast:   Snow tonight with snow showers persisting through the weekend.  

Long Range. Warmer and dry conditions will begin the last week of the year.

  

The Science:  A low pressure trough with an associate warm front bring a dose of snow tonight.  Westerly flow will kick in with a short lived convergence zone possible tonight.  A dirty (weak) ridge will slide into place tomorrow with light snow showers lingering through the weekend.

A warmer air mass will bring higher freezing levels on Monday with no significant snow events likely through the week.  

Confidence:  Good

Values from 4am today through 4am tomorrow.

Precipitation: Today 24hr water: .25 snow: 2-4    Tomorrow’s 24hr water: lt .25   snow: 1-3 Trend and Timing: Snow will arrive tonight and shift to intermittent showers tomorrow.

Temperature: Low: 17   High: 24 Freezing level: +-1500’ Trend and Timing:    Freezing levels will remain well below Pass level through tomorrow.

Winds Base: 0-10 E Ridge Top:  5-10 ESE shifting W Trend and Timing: East flow will strengthen today with winds shifting westerly tomorrow.  There may be a short period of gusty post frontal ridge top winds tomorrow morning.