The Storm

This is an extraordinarily interesting storm.  Features such as atmospheric river, tropical moisture and polar jet all mixed together makes for riveting storm watching. 

 

As you can see from the Sat. photo below, there is a ton of moisture being entrained from as far south as Hawaii.  The moisture is riding up an over the high pressure cell off the California coast.  The stream takes an almost 90degree turn west where it meets the polar jet.  

 

How and when the cold air aloft mixed with the moisture will determine how the  rain vs snow game will play out in the mountains.   Wind is also a major player with models showing 60knot winds above 5000’.   An impressive storm.   

 Enjoy the chaos.

start time sunday dec 1, 8:00 am

MOUNTAIN WEATHER FORECAST

Time and Day: 1000 Saturday

The Snapshot:  Light snow and rain today.  Heavy rain and high winds tomorrow changing to snow tomorrow night.

The Science:  The northern jet stream is taking direct aim at the PNW today while entraining a warm wet tropical air mass.   The warm air mass will meet the Polar jet late tomorrow night which will equate to moderate to heavy snow in the mountains on Monday.  But first, we will have to endure a ton of rain and high winds tomorrow.   

Storm totals.   Water content by noon tomorrow could exceed 3” of water (mostly rain).  6-10” of snow 4am Monday. An additional +-12” by 4am Tuesday.  Timing of cold air aloft and favorable orographics (convergence) could push these totals up.  

4-7day Long Range: Skies will clear on Tuesday with extremely cold temperature being ushered in from the north.  The remainder of the week looks cold and clear.

 

Precipitation:   Water by 4am = 1” Snow equivalent = 0   Total inches of water by noon tomorrow = 1.75 -2” + Total inches of snow by noon tomorrow = 0 at base 2-6 on ridge   Trend and Timing:   Light showers today with precipitation intensifying tonight.  Heavy rain is expected below Hogsback. The upper ridge will have its share of rain but with a mixture of snow.  The snow line hits the highway late tomorrow night.

Base Temp and Freezing levels:                                        Low: 32   High: 42 Freezing level:  4000’     5500’   Trend and Timing:   Freezing levels will rise just above 5000’ today.  Temperatures will begin fall midday tomorrow with freezing levels fall below 4000’ sometime tomorrow night.

Wind:   Base:  10-20 SWS Ridge Top: 15-30 W      Trend and Timing:   High wind advisory will be in effect for early tomorrow morning with gust above 50mph possible along the upper ridges.  Sustained winds above 25mph will be likely through most of the day tomorrow.

Lots of water on the way

This GFS precipitation model is for  Monday 4am.  Black represent 2'5 -4" of water in a 12 hour period.  Sunday/Monday will be extremely wet.  Let us hope that some of it is snow.   

START TME SAT NOV 30 8:00 AM

MOUNTAIN WEATHER FORECAST

 0830 Friday

The Snapshot: Light rain/snow mixture today. The precipitation gradually increases tomorrow.  Expect heavy mixed precipitation tomorrow night with rain on Sunday.  Snow Sunday night and Monday.  

The Science:  The first line of moisture is entering the north Puget Sound area this morning with light rain already falling in the mountains. Strengthening westerly flow will gradually increase the moisture during the next 24-36 hrs. A large warm air mass with a bunch of moisture is leading the charge. So expect heavy precipitation and high winds to begin late tomorrow night and last through Sunday.  The leading edge of the arctic cold front is now schedule to move past the mountain late Sunday afternoon or evening. Snow starts late in the day on Sunday and continues through Monday. 

Storm totals by 4pm Sunday exceed 3” of water.  How much of this will be rain?  That is the question of the day.  An additional 1-2” of water or 1-2 feet of snow will be possible by the end of Monday.  Storm details will be more fine-tuned tomorrow.

4-7day Long Range:  A cold arctic air mass dropping in from the Canadian interior pushes all the moisture south on Tuesday with high pressure developing over the PNW.   This translates to a very cold dry week. There are signs of another system entering the stage next weekend.

 

Precipitation:   Water by 4am = .25  Snow equivalent = 1-2     Total inches of water by noon tomorrow = .25 -.5 Total inches of snow by noon tomorrow = 2-4   Trends and Timing:   Rain with snow mix above 4500’ will begin today. With some luck, the upper mountain will mostly snow.  Intermittent showers continue through the night with precipitation intensifying during the day.

Base Temp and Freezing levels:                                        Low: 32   High: 34 Freezing level: +-4500      5000’   Trend and Timing:   Freezing levels will hover around 4500’ tonight.  Temperatures will be just above freezing tomorrow with freezing levels spiking up to 6000’ on Sunday morning.

Winds:   Base: 0-5 W   Ridge Top: 5-10 W     Trend and Timing:   Winds will not be much of a factor until Sunday.  A high wind event is expected to accompany Sunday’s storm.

 

 

 

MOUNTAIN WEATHER FORECAST

10:30am Thursday

The Snapshot: All the living turkeys will enjoy a few more days of warm sunny weather.  It will not last for long, change is in the air.

 

The Science:  Warmer western air, pushed by the northern jet stream, will wash out the chilly air trapped in the eastern basin today. This will rise freezing levels in the mountains and enable the developing systems to enter the region.  A warm front arriving early Saturday morning will bring light rain with periods of mixed snow starting tomorrow night and lasting through early Sunday morning. 

 

The timing of the strong frontal system tracking in on Sunday is still in question.  As of now it appears that this system could start out as heavy rain in the morning with the rain changing to snow later in the day.  Heavy snow is expected Sunday night into Monday.

 

4-7day Long Range: Snow with freezing levels below 500’ is likely to persist into Monday.  High pressure developing on Tuesday will bring a return to the sun with very cold temperatures.  Long range models have this dry cold period lasting through all of next week.  

Precipitation:   Water by 4am = 0 Snow equivalent = 0   Total inches of water by noon tomorrow = 0 Total inches of snow by noon tomorrow = 0   Trend and Timing:   Today will be dry with increasing clouds.

Base Temp and Freezing levels:                                        Low: 34   High: 45 Freezing level:         5500’     4500’   Trend and Timing:   Freezing levels will rise above 5000’ today.  Temperatures drop slightly tomorrow with freezing levels reaching 4500’ late afternoon or evening.

Winds:   Base: 0-5 E shifting W Ridge Top: 0-5 E Shifting W   Trend and Timing:   Winds will shift westerly tonight.  Winds won’t be a factor until Sunday.

start time november 29th friday 8:00 am

Start Time Thursday 28th---8am

MOUNTAIN WEATHER FORECAST

Time and Day: 1030 Wednesday
 

The Snapshot: Partly cloudy today and tomorrow with dry conditions prevailing in the mountains through Friday.

The Science:  After a few more days of fairly benign weather, the polar jet is expected to take aim at the PNW.  This will open the door for a strong frontal system with abundant moisture to track through the PNW over the weekend. 

4-7day Long Range: As of now, this is how it is looking like it will play out:  Light rain reaching the mountains late Friday afternoon with freezing levels around 5000’.  Freezing levels drop to 4500’ on Saturday with mixed snow and rain. A strong cold front arrives early Sunday morning with heavy snow in the mountains possible.   Of course, this is still a few days out so I will be watching this closely as the timing and details become more clear. 

High pressure begins to rebuild on Monday for another prolonged dry period to start the new month.   

Precipitation:   Water by 4am = 0 Snow equivalent =0   Total inches of water by noon tomorrow = 0 Total inches of snow by noon tomorrow = 0   Trends and Timing:   The atmosphere will remain dry through Friday.

Base Temp and Freezing levels:                                        Low: 30    High: 42 Freezing level: 4000’    5000’   Trend and Timing:      Freezing levels will slowly rise during the next 24hrs as the easterly flow gets overtaken by warmer western air.  Daytime temperatures could touch 50f tomorrow afternoon.   Surface temperatures will remain on the warm side through Friday.

Winds:   Base: 0-10 E  shifting W Ridge Top: 5-10 E shifting W   Trend and Timing:   Winds will shift westerly tomorrow night in preparation of the incoming system on Friday.

The Polar Jet

The polar jet forecast model is looking promising for Sunday/Monday. Moderate to heavy snow with freezing levels near sea level is possible.   We will likely have to endure a little rain Friday and Saturday but December should start out with some new snow.  Stay tuned….

MOUNTAIN WEATHER FORECAST

Time and Day: 1000 Tuesday
 

The Snapshot: The Cascade Mountains and most for interior will stay dry today with high clouds. Clear and sunnier tomorrow.

 

The Science: A weak system tracking south along the Washington coast will maintain high cirrus clouds over the PNW for today.  The skies will begin to clear tonight as the pressure increases over the inland NW.  This pattern will continue through early Friday morning.

 

4-7day Long Range:  The next system of interest enters the scene on Friday.  GFS and NAM models have a low pressure system developing off of the BC coast and tracking south into Washington over the weekend.  As of now, light precipitation begins midday on Friday with freezing levels between 4000’ and 5000’ (rain).  The precipitation intensifies on Saturday with freezing levels falling to around 4000’.   A strong cold front pushes in late Saturday night with lowering freezing levels and snow for Sunday and Monday.  All these details will likely change since it is still 4-7 days out.   Snow dancing will help.    

Precipitation:   Water by 4am = 0 Snow equivalent = 0   Total inches of water by noon tomorrow =0 Total inches of snow by noon tomorrow = 0   Trends and Timing:   Dry conditions will continue through early Friday morning.

Base Temp and Freezing levels:                                       Low: 30    High: 40 Freezing level: +-5000’   Trend and Timing:      Freezing levels will continue to hover right around the 5000’ level through early Friday morning. Clear skies and chilly air trapped in the eastern basin will allow early morning temperatures to drop below freezing.

Winds:   Base: 0-5 E Ridge Top: 0-10 E   Trend and Timing: East flow will continue through Thursday.