*2:30pm 12/1 Update: Bulk of accumulation in Colorado and Utah arrives Saturday evening (12/2) through Sunday (12/3).

Tomer’s Take: The ‘golden combo’ of a moderate to strong intensity atmospheric river, stacked WNW Flow, and high ratios is underway in PNW, BC, ID, WY, UT, and C+N Colorado mountain zones. It’s a three day event, 12/1-12/3, with snow lasting into 12/4 in the Tetons. 1-3 feet at many ski resorts.

My forecast update:

About 6 inches at Aspen Mountain with another foot or more to go.

Current Setup

Water vapor satellite shows the moderate to strong intensity atmospheric river slamming into the PNW with downstream benefits.

Atmospheric River

Forecast Integrated Vapor Transport (IVT) for the WA/OR coast 46.5N/124W. ‘Moderate to strong intensity’.

Forecast Jet Stream

Valid 12/2. Powerful WNW Flow stacked to 10k.

Valid 12/9. Deep trough sinks far to the south and might cut-off.

Forecast Radar & Satellite

Forecast Totals

*Updated 2:30pm 12/1: Additional Snow Accumulation

Bulk of snow accumulation in Colorado and Utah occurs Saturday evening (12/2) through Sunday (12/3).

Jackson Hole, WY snow plume, accumulation over time.

*Updated 2:30pm 12/1.

*Updated 2:30pm 12/1.

VT/NH/ME Snow: Late 12/1-12/2 (Light), 12/3-12/4 (Moderate to Heavy).

*Updated 2pm 11/30. Forecast is on track, no big changes.
Tomer’s Take: A golden combination of jet power, stacked WNW Flow, and moderate to strong intensity atmospheric river (AR) contribution delivers 1-3 feet of accumulation in parts of the PNW, BC, ID, WY, UT, and CO. My forecast numbers for CO are back up – I think the AR contribution and air temps are enough to close the gap.

My forecast video:

Current Setup

Water vapor satellite shows the moisture aloft loading-up with an atmospheric river (AR) reach.

Orange/red = drier air aloft. Moisture = white/blue.

Forecast Jet Stream

Valid 12/2. Powerful WNW Flow stacked down to 10k.

Valid 12/9. Storm system with amplified jet sliding through the interior Rockies.

Atmospheric River

Forecast Integrated Vapor Transport (IVT) valid through 72 hours ending 12/5. The fetch of moisture transport can be traced through the very western Pacific basin.

Forecast IVT valid next 10 days for OR/WA coast at 46.5N/124W. Moderate to strong intensity atmospheric river contribution is likely.

Forecast Radar & Satellite

Forecast Totals

*Updated 2pm 11/30. Forecast is on track, no big changes.

CO Snow: Late 11/30-12/3.

UT Snow: 12/1-12/3.

WY Snow: 12/1-12/3.

PNW Snow: 12/1-12/6.

*Updated 2pm 11/30.

Forecast Snow Accumulation Over Time for mid-mountain Jackson Hole, WY.

*Updated 2pm 11/30.

VT/NH/ME Snow: 12/1-12/2 (Light to moderate accums), 12/3-12/4 (Heavy).

Tomer’s Take: Both jet streams become active and deliver moisture 11/30-12/5. Plus, the northern branch appears to setup a WNW Flow pattern with big snow accumulation in PNW, BC, ID, WY, UT, and CO. The rich flow in the PNW is associated with a moderate to strong intensity atmospheric river (AR).

My Afternoon forecast video update:

Current Setup

Water vapor satellite shows both jets escorting storm systems.

Orange/red = drier air aloft.

Forecast Jet Stream

Valid 12/2. WNW Flow down to 10k delivers with efficiency.

Valid 12/8. Storm system slides into PNW then interior Rockies.

PNW Atmospheric River

Forecast Integrated Vapor Transport (IVT) for WA/OR coast at 46N/124W. A moderate to strong atmospheric river intensity is likely.

WNW Flow Pattern

Valid 12/3. Forecast 10,000ft flow shows the WNW orientation.

Valid 12/3. Forecast 10,000ft moisture (RH%) and streamlines. An efficient flow for the Central and Northern Mountain zones.

Forecast Radar & Satellite

Forecast Snow Totals

*Updated 230pm 11/29: Flow not as strong in CO, cut forecast totals by about 30%

Snow Timeline Cheat Sheet ->

PNW: PM 11/30-12/5, 12/7-12/8

ID: 12/1-12/7

WY: 12/1-12/4, 12/8.

UT: 12/1-12/4, 12/8.

CO: PM 11/30-12/4, 12/8-12/10.

*Updated 230pm 11/29.

*Updated 230pm 11/29.

Tomer’s Take: Both jets turn active 11/30-12/7 with heavy snow likely in the PNW, BC, ID, WY, UT, CO.

In the Northeast, heavy snow accumulation is possible with a coastal storm system 12/3-12/4.

My forecast video:

Crystal clear view of Cody Bowl at Jackson Hole. Next snow arrives late 11/30-12/4.

Current Setup

Water vapor satellite shows what’s coming. Both jets deliver a series of storm systems.

Orange/red = drier air aloft.

Forecast Jet Stream

Valid 11/29. The first minor storm system takes a southern track and helps to break down a small ridge of high pressure.

Valid 12/2. Moist flow into the PNW/BC and storm system moving through WY, CO, NM.

Valid 12/7. Powerful jet running into the PNW and storm system sliding through MT, ID, WY, UT, CO.

Forecast Radar & Satellite

Forecast Totals

*Updated 4:30pm 11/28.

*Updated 4:30pm 11/28.

WY Snow: Late 11/30 through early 12/4 (bulk 12/2-12/3), and 12/6-12/8.

UT Snow: Late 11/30 through early 12/4 (bulk 12/2-12/3), and 12/6-12/8.

CO Snow: 12/1-12/4, and 12/7-12/8.

*Updated 4:30pm 11/28.

*Updated 4:30pm 11/28.

Tomer’s Take: A brief ridge of high pressure dominates through 11/29 then it starts to break down. An active pattern takes shape 11/30-12/6 with both jets contributing.

My video Forecast:

7 inches in 24 hours reported at Killington, VT:

It’s a clear morning at Loveland Ski Area. 12,000ft air temps are around zero. Next snow arrives 12/1-12/4.

Current Setup

Water vapor satellite shows the next area of low pressure approaching CA. This low will take a southern track riding the southern jet. It will help to break down the brief ridge of high pressure.

Orange/red = drier air aloft.

Forecast Jet Stream

Valid 11/28. Notice the shortwave trough sliding into CA.

Valid 12/1. An area of low pressure with jet support moves through UT, WY, ID, CO. Moisture transport continues into the PNW.

Valid 12/6. Riding over the Intermountain West. Rich moisture transport into the PNW.

Forecast Radar & Satellite

Forecast Snow Totals

*Updated 4pm 11/27.

*Updated 4pm 11/27.

Valid 11/30-12/6.

WY Snow: 12/1-12/5 (Bulk 12/2-12/4)

UT Snow: 12/1-12/4.

CO Snow: 12/1-12/4.

NM Snow: 11/30-12/3.

Tomer’s Take: The higher elevations of the Northeast get moderate to heavy snowfall late 11/26 into 11/27 (with rain at lower elevations). Snow levels start high around 2k-3k then drop with bulk of snow in northern VT, NH, ME. Out West, high pressure takes over through 11/29 then the pattern shifts with both jet streams delivering snow 11/30-12/5.

My forecast video:

Forecast Jet Stream

Valid 11/28. High pressure ridge remains in place through 11/29, but notice the shortwave trough sliding into CA. This low pressure will take a southern track and help break down the ridge.

Valid 12/1. Active flow with both jets. Notice the storm system sliding through UT/WY/CO. And, powerful flow into the PNW/BC.

Valid 12/5. Flow turns temporarily quiet, but notice the trough in the Pacific lurking.

Forecast Radar & Satellite

Forecast Totals

CO/NM Snow: 11/30, 12/1, 12/2, 12/3.

UT Snow: 11/30, 12/1, 12/2, 12/3, 12/4 (Bulk occurs 12/2-12/3)

WY Snow: 12/2-12/5.

PNW Snow: 11/30-12/7.

NE Snow: Late 11/26-11/27.
Snow levels run 2k-3k initially then drop.

Tomer’s Take: Snow is moving out of UT & WY and into CO & NM with snow accumulation through 11/25. Then, the pattern shifts with high pressure ridging 11/26-11/29. The jet resets 11/30-12/5 with a stormier pattern and potential moisture loading on both jets.

My forecast video:

Forecast Radar & Satellite

Forecast Totals

Bulk of this accumulation occurs after after 11/29.

Both north and south jets become active 11/30-12/5.

Tomer’s Take: A Canadian cold front is diving south through WY into UT, CO and NM 11/23-11/25. Forecast snow totals are down slightly (-15%), but snow ratios remain high with much colder air. Then it’s a drier stretch with high pressure ridging 11/26-11/30. Pattern might turn stormier after 12/1 as jet resets.

My forecast video:

Current Setup

Water vapor satellite shows the Canadian cold front diving south.

Orange/red = drier air aloft.

Forecast Jet Stream

Valid 11/24. Door is wide open for colder air to plunge south through MT, WY, UT, CO, NM.

Valid 12/2. After high pressure ridging 11/26-11/30, the jet resets and turns more active for the West on/after 12/1.

Forecast Radar & Satellite

Forecast Snow Totals

Forecast totals are down slightly but ratios remain high with much colder air.

Tomer’s Take: The next western storm system hits 11/22-11/25 in MT, UT, WY, CO, and NM. It delivers much colder air and higher snow ratios. Then, the pattern shifts with a much drier stretch through 11/30 and high pressure ridging. Stormier pattern might develop on/after 12/1 as jet stream resets.

Snow continues today across the higher elevations of VT, NH, and ME.

My forecast video:

You can see the problem at Jackson Hole, 11/22 @7am. The snow line is halfway up the mountain. We need colder air to drop the rain/snow line down to the valley floor. The next cold front will do just that with much colder air on/after 11/23.

Current Setup

Water vapor satellite shows the lurking Canadian cold front. It dives south through MT on 11/22.

Orange/red = drier air aloft.

Forecast Jet Stream

Canadian cold front dives south through UT & CO into NM.

Drier period 11/26-11/30 with high pressure ridging. Pattern turns stormier on/after 12/1 as jet resets.

Forecast Radar & Satellite

Forecast Snow Totals

*Updated 4pm 11/22.

MT Snow: 11/22-11/23.

WY Snow: 11/23.

UT Snow: PM 11/23-11/24.

CO Snow: Late 11/23, 11/24, 11/25.

NM Snow: PM 11/24-11/25.

*Updated 4pm 11/22.

Much drier 11/26-11/30. Pattern starts to shift on/around 12/1 with snow developing in CA.

Tomer’s Take: A Canadian cold front races south through MT, WY, UT, CO, and NM between 11/23-11/25. The flow shifts after 11/25 and turns much drier through 11/30.

Clear as a bell this morning at Alta, UT. Snow arrives around 5pm on 11/23.

Crystal clear at Loveland Ski Area. Snow arrives around 5pm on 11/24.

Current Setup

Water vapor satellite shows the next storm system in the PNW/BC and Canadian cold front.

Orange/red = drier air aloft.

Forecast Jet Stream

Valid 11/24. Jet supports Canadian cold front digging south. Door is wide open for colder air.

Valid 11/30. Quiet Intermountain West with bulk of energy directed to PNW/BC and to Northeast.

Forecast Radar & Satellite

Forecast Snow Totals

*Updated 2pm 11/21.

MT Snow: Late 11/22 through early 11/24.

UT Snow: Late 11/23 through early 11/25.

CO Snow: Late 11/23 through 11/25.

NM Snow: 11/24-11/25.

*Updated 2pm 11/21.