Tomer’s Take: A major pattern shift hits the West 1/5-1/12. It’s comprised of a 2-3 storm cycle with colder temps and heavy snow accumulation. Before it arrives, a southern track storm system departs CA and slides through UT/AZ/NM/CO 1/3-1/5 with light to moderate snow accumulation. In addition, a vanguard area of light snow races through ID/MT/WY/UT/CO on 1/5.

In the Northeast, moderate to heavy snow accumulation is likely 1/6-1/7. If this stormtrack wobbles north then snow totals increase in VT/NH/ME. A 2nd powerful storm system arrives 1/9-1/10 with 70mph gusts and heavy snow changing to a rain/snow mix.

My afternoon forecast video update:

Current Setup

Water vapor satellite shows the southern track storm system departing CA, and the powerful pattern changing area of low pressure in the north Pacific.

Orange/red = drier air aloft.

Forecast Jet Stream

Pattern changing low diving south from AK/Canada into PNW. Vanguard snow races through Intermountain West 1/5.

Deep trough slides through Intermountain West.

2nd storm system with broad trough traverses the West with cold and snow. A 3rd storm might arrive after.

Forecast Radar & Satellite

Forecast Totals

Grand totals from 2-3 separate storm systems. Doesn’t all accumulate at one time.

*Updated 4:30pm 1/3.

These totals include both 1/6/-1/7 storm system and 1/9-1/10 storm system. 1/6-1/7 stormtrack has wobbled back north a touch increasing these totals. 1/9-1/10 is a powerhouse with 70mph gusts and heavy snow possibly changing to a rain/snow mix.

Tomer’s Take: A major Western pattern shift delivers colder air and big snow totals 1/5-1/11. It’s comprised of vanguard snow 1/5 then two storm systems. #1 occurs 1/6-1/8 followed by #2 on 1/9-1/11. Before all that happens, a storm system hits the Sierra late 1/2-1/3 then takes a southern track through AZ/UT/CO/NM 1/3-1/4.

In the Northeast, the 1/7 stormtrack continues to wobble. If it wobbles back to the north then snow totals increase VT/NH/ME. Another large storm system is possible 1/9-1/10.

My afternoon forecast video update:

Current Setup

Water vapor satellite shows two large storm systems in the north Pacific. The first storm system hits the Sierra late 1/2-1/3 then takes a southern track 1/3-1/4 through AZ/UT/CO/NM. The 2nd powerful storm system is the pattern changer.

Orange/red = drier air aloft.

Forecast Jet Stream

Valid 1/5. First key snow window is 1/5-1/8. The northern branch buckles south with a pattern changing area of low pressure. Vanguard snow races through the Intermountain West.

Valid 1/8. First trough moves east of the Rockies. This marks the end of key window #1. Key window #2 arrives 1/9-1/11.

Valid 1/10. Northern branch buckles south with 2nd large trough. Snow and cold.

Forecast Radar & Satellite

Forecast Totals

CA Snow: Late 1/2-1/3. Rain/snow line starts at 7000′ then drops to 5000′.

UT/AZ Snow 1/3-1/4.

CO/NM Snow: 1/4-1/5.

Forecast includes two storm systems. Key snow windows: 1/5-1/8, 1/9-1/11.

1/7 stormtrack continues wobble. If it wobbles north then snow totals increase VT/NH/ME.

Another large storm system possible 1/9-1/10.

Tomer’s Take: The start of 2024 is mild but a large Western pattern shift is lurking 1/6-1/10. The Polar Jet buckles to the south from Canada and delivers colder air along with widespread snow for UT/WY/ID/CO/MT. California also has a few chances for snow in the Sierra. In the Northeast, we’ll have to watch the storm track on 1/7 closely as a large storm moves within striking distance of VT/NH/ME followed by another large storm system around 1/9-1/10.

My afternoon forecast video update:

Current Setup

Water vapor satellite shows a few different areas of low pressure stacked-up in the north Pacific. All three are players across the West. Low #1 hits CA with snow late 1/2-1/3 (above 7K) then takes a southern track with snow for AZ/NM/UT/CO on/about 1/4. This opens the door for the other storm systems and pattern shift.

Orange/red = drier air aloft.

Forecast Jet Stream

Valid 1/5. The Northern Branch buckles to the south escorting an area of low pressure into the PNW/BC. A 2nd storm system is riding its coattails.

Valid 1/10. Potential 3rd storm system digging south through Intermountain West.

Forecast Radar & Satellite

Forecast Totals

Southern track storm exits CA and delivers snow to UT/AZ/NM/CO on/about 1/4.

Northeast:

Closely watching storm track on 1/7 with a large storm system passing just south of VT/NH/ME. If it shifts north then heavy snow is possible. Another strong storm system is possible 1/9-1/10.

Tomer’s Take: Confidence is increasing for a significant Western pattern shift after 1/5. The key snow/cold window for UT/WY/ID/MT/CO is 1/6-1/9 with a two storm combo.

The Northeast might benefit from this Western pattern shift. For now, I’ll assume a perfect (best/worst case) setup and trim forecast in coming days.

My afternoon forecast video update:

Forecast Jet Stream

Valid 1/5. Here comes the pattern changing trough dropping south from AK/Canada into PNW.

Valid 1/8. Powerful jet, colder air, and energy sliding through Intermountain West.

Forecast Totals

CA Snow: Late 1/2-1/3, 1/6, 1/8.
Wasatch Snow: 1/6-1/9.

CO Snow: 1/4-1/5, late 1/6-1/9.

Teton Snow: Late 1/5-1/9.

Northeast best/worst case forecast assuming perfect ingredients.

VT/NH/ME Snow: 1/7, 1/9.

Tomer’s Take: The warm & dry stretch for UT/WY/MT/ID/CO finally comes to an end after 1/5. The Polar Jet dives south from Canada with colder air and a storm system 1/6-1/8 with more widespread snow accumulation. Until then, we’re in what meteorologist Cory Gates calls ‘Closed Low Syndrome’.

My afternoon forecast video update:

Current Setup

Water vapor satellite shows three areas of low pressure lined-up in the Pacific with a West Coast trajectory.

Orange/red = drier air aloft.

Forecast Jet Stream

Valid 1/5. Notice the buckling Northern Branch and trough. This is the leading edge of colder Canadian air.

Valid 1/8. Pattern Change: A deep trough and area of low pressure move through UT/WY/CO/ID/MT along with colder air and snow accumulation.

Forecast Radar & Satellite

Forecast Totals

CA Snow: 1/3 & 1/6. Heaviest above 8,000ft.

Northeast: 99% of this accumulation occurs 12/30.

Tomer’s Take: Four different areas of low pressure are lined up for the West Coast and primarily California through 1/7. It’s a mild flow with heavy snow accumulation only at higher elevations. Very little moisture survives the trip into UT/ID/MT/WY/CO through 1/5. The pattern starts to shift after 1/5 with colder air rotating south from Canada into the Lower 48 and a storm system.

My afternoon forecast video:

Current Setup

Water vapor satellite shows an active Pacific flow with strong areas of low pressure lined-up. Main impact is to West Coast.

Forecast Jet Stream

Valid 1/6. A deep trough and colder air dives south into the Lower 48. This could be the pattern changer.

Valid 1/7. Same trough moves east with jet support.

Forecast Radar & Satellite

Forecast Totals

CA higher elevations get bigger totals. Mount Shasta could see 10-20 inches afternoon 12/29 through morning 12/30 above 10,000ft.

UT Snow: 1/4 (light), 1/6-1/7.

WY Snow: 1/1 (light), 1/6-1/7.

CO Snow: 12/31 (light), 1/4 (light), 1/7.

VT/NH/ME: 12/30 (light), 1/4 (light to moderate).

Tomer’s Take: A challenging dry stretch ahead for the Intermountain Rockies including UT/WY/MT/ID/CO through 1/5. After 1/5 a pattern change is possible. Before 1/5 the storm track favors the West Coast including British Columbia/WA/OR/CA.

My afternoon forecast video update:

Current Setup

Water vapor satellite shows an active Pacific storm track with West Coast/BC trajectory.

Orange/red = drier air aloft.

Very little of this moisture survives the trip beyond the West Coast.

Forecast Jet Stream

Valid 1/3. Trough of low pressure rolls through CA/West Coast.

Valid 1/6. Another trough moves through CA/West Coast and into the Interior Rockies. I like the position of the Northern Branch and this could mean more of a pattern shift with colder air.

Stratospheric Warming

We look for clues in the Stratosphere as to what might occur in the Troposphere (lowest part of the atmosphere where we live). This is a macro forecasting tool.

One indicator shows warming in the Stratosphere in 10-15 days. This suggests a shift of the vortex over the North Pole. This can mean colder air is released and rotates south into the Lower 48.

Below, the forecast graphic from the ECMWF points to a shift in the Polar Vortex in 10-15 days. This *might* indicate a cold blast for the Lower 48.

Forecast Radar & Satellite

Forecast Totals

VT/NH/ME rain 12/28-12/29, changing to light snow 12/30.

Tomer’s Take: This is a challenging period with mostly dry conditions across the Intermountain West and rain (again) in the Northeast. The main storm track impacts BC/WA/OR/CA, but very little of this moisture survives the trip into the Interior Rockies.

My forecast video:

Current Setup

Water vapor satellite shows an active Pacific storm track aiming at BC/West Coast. But, very little of this moisture survives the trip into the Interior Rockies.

Orange/red = drier air aloft.

Forecast Jet Stream

Trough of low pressure approaches the West Coast.

Cold air remains trapped in Canada with northern branch. Active subtropical jet delivers a storm system to the Intermountain Weather 1/3-1/5.

Forecast Radar & Satellite

Forecast Totals

PNW/BC rain/snow lines fluctuates 4500′-5500′.

UT Snow: 1/3-1/4.

WY Snow: 1/4.

MT Snow: 1/4.

CO Snow: 1/4.

VT/NH/ME Rain 12/27-12/29, changing to snow 12/30.

Tomer’s Take: Snow will come to an end in Colorado tonight then light wraparound snow on 12/26 returns mainly east of the Divide. PNW/BC gets snow 12/25-12/28 above 5k-6k. Tahoe gets light snow late 12/27, and moderate snow accumulation 12/29-12/30. Still watching the possibility of a New Year’s Eve storm system for the Interior Rockies.

My afternoon forecast video:

Forecast Totals

CO Wraparound light snow 12/26.

CA light snow late 12/27 for Tahoe & Mammoth. Heavy for Mount Shasta.

CA moderate snow accumulation 12/29-12/30.

VT/NH/ME rain 12/27-12/28, light snow 12/29. Possible heavier snow 1/2-1/3.

Tomer’s Take: Two areas of low pressure deliver snow to UT/WY/CO 12/23-12/24. A major storm system hits the PNW/BC with heavy snow 12/25-12/26, and the Sierra might get heavy snow 12/29-12/30.

A storm system crosses the Intermountain West on/about 12/30-12/31 with light to moderate snow accumulation.

My forecast video:

5″ in 24hrs at Alta, UT with another 1-3″ before the storm departs.

Current Setup

Water vapor satellite shows both areas of low pressure merging over UT/WY/CO.

An active Pacific jet inbound to PNW/BC.

Orange/red = drier air aloft.

Forecast Jet Stream

Forecast pattern 1/1/2024. Active flow with both northern and southern branches.

Forecast Totals

UT Wasatch: An additional 1-3 inches 12/23 then drier 12/24 (and beyond).

CO Snow: 12/23-12/24 & 12/30-12/31.

CA Snow: 12/27 (light), 12/29-12/30 (Heavy).

VT/NH/ME: Rain on 12/27 and it *might* change to snow 12/28. Light snow 12/30-1/1.