December 5, 2016

8:00start Tue Dec 5th abs


Time and Day:  0700 Monday

The Snapshot:  Colder temperatures with snow today,   Poof-da.
A drying trend begins tonight with more snow expected on Thursday and Friday.  The PNW snow machine continues to run through the weekend.

The Science:  This morning’s radar has snow showers falling over Puget Sound and should reach Stevens Pass by daylight.  Light snow will fall through the day as the approaching low-pressure cell tracks east over the next 8-12 hrs.   Temperatures will continue to fall as cold air from fills in on both sides of the Cascades Crest.  For you mountain weather geeks, this is referred to as the Frazer River Outflow.  Stevens Pass could see single digit low temperatures during early morning hours.

 A small high pressure cell that has formed offshore will bring and end to the snow tonight as it makes its way inland.  Therefore, expect a few days of dry and cold weather before the next systems approaches.   Strong east/west pressure gradients develop over the mountains so watch for strengthening east/offshore winds as the week progresses.

The Long Range:  Higher freezing levels with moderate precipitation will begin on Thursday.  Snow is likely to fall through the weekend under steady westerly flow.

Precipitation Ending at 4am:

Today 24hr water = .25+ Snow = 2-5

Tomorrow’s 24hr water = 0 snow = 0

Trend and Timing:
Snow showers tapering off after sunset.  Water content will be low due to the cold dry air aloft. 

24hr temperature ending at 4 am tomorrow: 
Low:  10   High: 22
Freezing level: +-500 - 0

Trend and Timing:   
Temperatures will continue to fall.  Freezing levels could reach sea level early Wednesday morning.

24hr Winds (mph) ending at 4 am tomorrow:
Base:  0-10 E
Ridge Top:  5-15 E

Trend and Timing:
East flow will develop today and strengthen over the next 24-36 hrs.


December 4, 2016

8:00 Start Mon Dec 5th abs


Time and Day: 1100 Sunday

The Snapshot: Snow tapering off with clear periods this afternoon.  More snow and continued cooling tomorrow.  Cold and dry for Tuesday and Wednesday, with more snow and warming to wrap up the week.   

The Science:  Whew, what a storm with +20” of snow and counting.  The convergence showers are starting to wane with partial clearing beginning.   Pressure gradients will ease a bit today which will produce a short break in the precipitation through early tomorrow morning.  Strong northwest flow will usher in the more cold air with freezing levels dropping to or below 500’ tomorrow. 

A low-pressure trough will track through tomorrow with more snow for Stevens.   A high pressure ridge will strengthen tomorrow night which will produce dry, cold and clear conditions Tuesday and Wednesday.   Cold temperatures will settle in with early morning temperatures in the lower teens tomorrow and possibly single digits by Wednesday morning.   

The Long Range:   More excitement starts on Thursday as the next series of frontal systems prepares to enter the region.   Details are still in question, but snow is likely with warming starting Thursday and lasting into the weekend.

Precipitation Ending at 4am:

Today 24hr water = .25 Snow = 1-3

Tomorrow’s 24hr water = .25-.5 snow = 3-6

Trend and Timing:
Snow will begin again after 4am tomorrow.  Snow diminishes to showers through the afternoon hours.

24hr temperature ending at 4 am tomorrow: 
Low: 12    High: 20
Freezing level: 1500’ - 500’

Trend and Timing:   
Temperatures will continue to drop through the next 24hrs.

24hr Winds (mph) ending at 4 am tomorrow:
Base:  5-10 W shifting E
Ridge Top:  5-15 W gusty

Trend and Timing:
Gusty westerly winds will slowly diminish today and shift easterly tomorrow.


December 3, 2016

6:15 start sun dec 4th ABS

Mountain Weather Forecast

Time and Day: 0645 Saturday

The Snapshot: Light snow showers today, cooler. Heavy snow tonight and Sunday morning with very cold temperatures. Snow ending Sunday mid-morning.

The Science: Yesterday’s warm front stalled near the coast for long enough that the cool air behind it mitigated the effects of the warm-up. Stevens Pass saw 34 degrees in the base area and “sn-aining.” There is 3 inches in the base area this morning and 7 inches on the upper mountain with a nice cooling trend.

For the remainder of the day and early Sunday the Central Cascades will be under strong W-NW upper level flow with lots of unstable, moist air upstream. This pattern particularly favors Stevens Pass. The action should ramp up after 4pm, with snow becoming heavy in the evening hours and continuing through daybreak on Sunday. As the arctic air mass moves into the forecast area in the early morning hours on Sunday, it will push the moisture stream south, leaving Stevens Pass in very cold and dry air aloft. Showers should end abruptly Sunday mid-morning.

Models currently indicate a weak trough crossing Washington during the day Monday, potentially bringing a few more inches of snow. Freezing levels should be near the surface with temperatures in the teens at Stevens Pass.

The Long Range: After the trough moves through on Monday, Washington will be under cool, light northerly flow Tuesday and Wednesday. This will bring dry and cold conditions. Models currently have a ridge building over the West Coast midweek, and more active weather with seasonal norm temperatures at the end of the week.

Precipitation Ending at 4am:

Today 24hr water = 1-1.25 Snow = 14-16”

Tomorrow’s 24hr water =  .25 snow = 2-4

Trend and Timing:
Light snow showers should continue during the day Saturday, becoming heavy after 4pm. Heavy snow will continue all night and into Sunday morning, ending abruptly mid-morning. Day 2 precip amounts will mostly fall in the first few hours of that 24 hour period.

24hr temperature ending at 4 am tomorrow: 
Low:  22   High: 30
Freezing level: 3500-1000

Trend and Timing:   
Temps will rise a little during the day time warming, but mostly remain cool. The arctic airmass enters our region after midnight bringing a strong cooling trend for Sunday morning.
24hr Winds (mph) ending at 4 am tomorrow:
Base: W 10-15
Ridge Top: W 20-30, Gusts to 45

Trend and Timing:
 Gusty westerly winds will strengthen throughout the day Saturday, peaking overnight. Ridgetop winds should turn more NW Sunday morning and relax to the teens.