Winter Forecast 2023-2024

Tomer’s Take: A Strong El Nino is likely with a screaming Subtropical Jet across the Southern Tier by January, February, March, April, and May 2024. I believe we’ll see a 30% El Nino Modoki contribution. This puts several major ski resorts on ‘The Bubble’. Atmospheric River (AR) setups are likely along with large East Coast storm storm systems.

My full forecast video:

Pikes Peak Ascent, Run Rabbit Run, Next Colorado Snow Inbound 9/14-9/15

Tomer’s Take: It’s a busy weekend ahead for athletes with both the Pikes Peak Ascent/Marathon and Run Rabbit Run 50/100M. Both events will have weather impacts early in the weekend, drier later. I’m forecasting new snow accumulation above treeline on 9/14 and 9/15 with a cold front and active Subtropical Jet Stream.

Pikes Peak Summit

Snow accumulated on 9/10-9/11. I’m forecasting an additional 3-6 inches between 9/14-9/15.

LIVE summit cam 9/13:

Setup

Below is the forecast jet stream valid 9/14-9/15. Notice the active Subtropical jet and cold front merger.

Snow

Below is forecast snow accumulation between 9/13-9/15. The lightest blue shade is 1-3 inches with escalating values by color. Some mountain locations above treeline (above 13K in particular) could see 6″ or more.

Mountain & Event Forecast

Pikes Peak, Summit Level.

9/14: PM 1-2 inches snow,10-25mph gusts, 25/37F.

9/15: 2-4 inches snow, 10-25mph gusts, 25/28F.

9/16: AM dry, sun, PM flurries, 10-20mph gusts, 20/39F.

9/17: AM dry, sun, PM 40% rain/snow, 15-25mph gusts, 25/43F.

Run Rabbit Run, 10K Level.

9/14: 100% rain after 8am, 44F to 36F.

9/15: Overcast and valley fog, AM 20% rain/snow, PM 40% rain/snow, 35/43F.

9/16: Dry, sun, 37/52F.

Longs Peak, Summit Level.

9/14: PM 3-6 inches snow, 31F to 21F.

9/15: AM 1-3 inches snow, 20/24F.

9/16: Dry, sun, 21/35F.

Nolan’s Course, Summit Level.

9/14: PM 2-4 inches snow, 20/37F.

9/15: 1-4 inches snow, 23/31F.

9/16: Dry, sun, 19/42F.

Snow on Colorado’s 14ers with More to Come

Tomer’s Take: The first snow of the season is covering some of Colorado’s 14ers including Longs Peak. Additional snow accumulation is likely through 9/15. 14er summit temps are now falling into the teens and 20s. Why? An enhanced Subtropical Jet Stream plus remnant moisture from a hurricane.

I also include a forecast for the Run Rabbit Run 50/100 in Steamboat.

Longs Peak Snow

First Snow of the season. Sometimes known as ‘Termination Dust’.

Pikes Peak Summit, 9/11:

The view from Copper Mountain of the 10-Mile Range. Photo courtesy Copper Mountain.

Subtropical Jet

This is a foreshadowing of what to expect this Winter. It acts like a conveyor belt escorting moisture and storm systems off the Pacific directly into the West.

Moisture

Below is forecast total precipitation between now and 9/15. This represents above normal precipitation by September standards. Most of this is rain/snow above Treeline with additional snow accumulation above 13,500′.

Mountain Forecast

Mount Yale, Summit Level

9/11: AM 30% snow, PM 90% rain/snow.

9/12: AM dry, PM 50% snow, 20/42F.

9/13: AM dry, PM 80% rain/snow.

9/14: AM 30% snow, PM 90% snow.

9/15: AM 30% snow, PM 90% snow, 21/35F.

Longs Peak, Summit Level

9/11: AM 30% snow, PM 90% snow, 24/25F.

9/12: AM dry, PM 20% rain/snow.

9/13: AM dry, PM 50% rain/snow.

9/14: AM 40% snow, PM 90% snow.

9/15: AM 50% snow, PM 90% snow, 20/25F.

Maroon Bells, Summit Level

9/11: AM dry, PM 40% rain/snow.

9/12: AM dry, PM 20% rain/snow.

9/13: AM dry, PM 70% rain/snow.

9/14: AM 40% snow, PM 90% snow.

9/15: AM 40% snow, PM 80% snow, 22/35F.

Run Rabbit Run, 9/15-9/16

There is a 50 and 100 mile offering.

Steamboat/Rabbit Ears Pass Area, 10K Level.

9/14: AM dry, then 80% rain/snow after 10am, 44 to 36F.

9/15: AM 40% rain/snow, PM 50% rain/snow, 34/38F.

9/16: Dry, clearing, 35/50F.

Foreshadowing Winter: Rain/Snow with Subtropical Jet hits Colorado 9/10-9/15

Tomer’s Take: Rain/Snow appear likely for parts of Colorado between the afternoon of 9/10 and 9/15. The 14ers could see snow accumulation. Why? The Subtropical Jet is back plus it will entrain some of CAT-5 Jova’s moisture. Remember it from May, June and early July? This is a foreshadowing of what to expect this Winter. My take, this will be a big Winter in parts of Colorado. I’ll release my complete Winter Forecast soon.

CAT-5 Hurricane Jova

The Subtropical Jet will absorb and then transfer some of Hurricane Jova’s moisture into Colorado between the afternoon of 9/10-9/15. This will encourage additional rain/thunderstorms/snow.

Subtropical Jet

Remember the Subtropical Jet when it was a major player during May, June and early July 2023? It nailed parts of the West with heavy precipitation. This is an efficient transport pattern.

Below is forecast jet stream level valid 9/11. Notice the Subtropical Jet is back.

Below is forecast precipitable water percent of normal valid afternoon of 9/10. Some of Jova’s moisture shield becomes entrained and transported.

Below is forecast precipitation valid 9/11. This represents above normal precipitation by September standards in Colorado.

Specifics – Mountain Forecast

Longs Peak, Summit Level

9/10: 90% PM Rain to Snow with accumulation, 26/33F.

9/11: 90% Snow with accumulation, 23/30F.

9/12: PM 40% Snow, 23/34F.

9/13: PM 30% Snow, 26/35F.

9/14: PM 60% Snow, 28/32F.

9/15: PM 60% Snow, 19/30F.

Chicago Basin, Summit Level

9/10: PM 30% Rain/Snow, 35/49F.

9/11: 40% Rain/Snow, 32/42F.

9/12: 80% Rain/Snow, 29/39F.

9/13: 90% Snow with accumulation, 27/32F.

9/14: 80% Snow, 25/37F.

9/15: PM 40% rain/snow, 21/40F.

Update: Labor Day Weekend Mountain Forecast

Tomer’s Take: A dip in the jet, trough of low pressure, and small surge of Monsoon moisture remains in my forecast for the West between 9/1-9/5. I say 9/5 now because there might be one additional small area of low pressure riding the coattails. This pattern delivers cooler mountain temps and rain/snow/thunderstorms. Snow accumulation appears possible across parts of higher elevation WY and MT. Overall, areas impacted 9/1-9/5 include PNW, Northern CAN, CO, UT, WY, ID, AZ, MT.

Current Setup

Water vapor satellite shows the shifting storm track in the PNW. This delivers a dip in the jet, trough of low pressure, and taps into a small surge of Monsoon moisture between 9/1-9/5. Red/orange = drier air aloft.

Active Jet

Below is the forecast jet stream valid 9/2. Notice the jet coddling an area of low pressure over CA/West Coast.

Trough

Below is forecast mid-atmosphere pressure anomalies valid 9/4. Notice the primary storm system over the Intermountain West, but also notice the second smaller area of low pressure riding its coattails. This may keep things active through 9/5.

Precipitation

Below is forecast precipitation valid 9/4. Green/blue = rain/snow/thunderstorms.

Specifics

Chicago Basin, CO

9/1: AM dry, PM 30% rain/thundestorms.

9/2: AM dry, PM 30% rain/thunderstorms.

9/3: AM dry, PM 40% rain/snow/thunderstorms.

9/4: AM 20% rain/snow, PM 30% rain/snow.

9/5: AM dry, PM 20% rain/snow/thunderstorms.

Kings Peak, UT

9/1: AM 10% rain/thunderstorms, PM 60% rain/snow/thunderstorms.

9/2: AM 20% rain/snow, PM 90% rain/snow.

9/3: AM dry, PM 100% rain/snow.

9/4: AM 60% rain/snow, PM 50% rain/snow.

9/5: AM 80% rain/snow, PM 20% rain/snow.

Grand Teton, WY

9/1: AM 60% rain/snow, PM 30% rain/snow.

9/2: AM dry, PM 20% rain/snow.

9/3: AM 40% snow, PM 90% snow.

9/4: AM 90% snow, PM 30% snow.

9/5: AM 70% snow, PM 40% snow.

Granite Peak, MT

9/1: AM 40% rain/snow, PM 30% rain/snow.

9/2: AM dry, PM 10% snow.

9/3: AM 20% rain/snow, PM 90% snow.

9/4: AM 80% snow, PM 80% snow.

9/5: AM 10% snow, PM 40% snow.

Labor Day Weekend Mountain Forecast Looks Active

Tomer’s Take: A dip in the jet stream, trough of low pressure, and small surge of Monsoonal moisture hits the Intermountain West between 9/1-9/4 then the pattern dries out. Who’s included? AZ, UT, NV, CO, WY, ID, MT. Precipitation will include rain, snow, and thunderstorms.

Storm System

Below is forecast jet stream level valid 9/2-9/3. Notice the dip in the jet stream over the West. This coddles a storm system, gathers moisture, and then moves across the Intermountain West.

Below is forecast mid-atmosphere pressure anomalies. The trough and area of low pressure are well-defined and sets the precipitation wheels in motion.

Precipitation

Below is forecast 24-hour precipitation valid 9/2. You can see the two sources of moisture. One with the storm system and the other from the Monsoon source region. Areas impacted include northern CA, OR, UT, ID, WY, ID, CO, AZ.

Below is forecast precipitation valid 9/4, Labor Day. The bulk of rain/snow/thunderstorms are associated with the storm system by this point in time. Areas impacted include UT, ID, WY, MT, CO and the PNW.

Specifics

Gannett Peak, WY

9/2: 50% PM rain/snow/thunderstorms.

9/3: 20% AM rain/snow, 70% PM rain/snow/thunderstorms.

9/4: 80% AM rain/snow, PM 80% rain/snow.

9/5: AM 20% rain/snow, PM drier.

Granite Peak, MT

9/2: 30% PM rain/snow/thunderstorms.

9/3: 40% AM rain/snow, PM 50% rain/snow/thunderstorms.

9/4: 80% AM rain/snow, PM 80% rain/snow.

Chicago Basin 14ers, CO

9/2: 20% AM rain/snow/thunderstorms, PM 60% rain/snow/thunderstorms.

9/3: 30% AM rain/snow/thunderstorms, PM 100% rain/snow/thunderstorms.

9/4: 50% AM rain/snow, 40% PM rain/snow.

Kings Peak, UT

9/2: 50% AM rain/snow, PM 80% rain/snow/thunderstorms.

9/3: 50% AM rain/snow, PM 100% rain/snow/thunderstorms.

9/4: 50% AM rain/snow, PM 20% rain/snow.

Curveballs: Labor Day Weekend Mountain Forecast and Beyond

Tomer’s Take: In my last update, I highlighted an active weather pattern for Labor Day Weekend and early September across the Intermountain West. The moisture will come in two waves, and you might even say curveballs. The first includes the remnants of a tropical system plus Monsoonal moisture 8/25-8/27, and a Monsoonal surge 8/31-9/2. Beyond this, an active jet stream and Monsoonal remnants produce above normal moisture through 9/15.

Tropical Remnants

Water vapor satellite clearly shows an area of low pressure tracking north from the 4-Corners. This is loaded with tropical moisture. Red/orange = drier air aloft. White/Blue = water vapor aloft.

8/25-8/27

Below is forecast total precipitation percent of normal through 8/27. The green/blue areas represent above normal precipitation. Some areas in UT, CO, WY, AZ, NM run 100-500% of normal.

And, some of this moisture will fall as rain/snow on the higher peaks especially in WY.

A few examples.

Granite Peak, MT:

8/25: AM dry, PM 50% rain/t-storms.

8/26: AM dry, PM 80% rain/t-storms/snow.

8/27: AM 30%, PM 90% rain/snow.

Gannett Peak, WY:

8/25: AM dry, PM 50% rain/t-storms.

8/26: AM dry, PM 40% rain/t-storms/snow.

8/27: AM 30%, PM 90% rain/snow.

Labor Day Weekend

Below is forecast precipitation over Labor Day Weekend. The green represents actual precipitation. You’re looking at a Monsoonal surge across AZ, NM, UT, CO.

September 1-15

Below is forecast precipitation percentage of normal. An active jet stream generates above normal precipitation across parts of the West in green including WY, UT, NV, CO, ID.

Bottom Line

The atmosphere is throwing a few curveballs.

  1. Tropical remnants
  2. Late Monsoon (into September)
  3. Active late Summer Jet (into September)

Hilary could hammer the Western High Peaks with snow and wind

Tomer’s Take: The remnants of Hurricane Hilary could impact many of the high peaks across the West 8/20-8/21 with strong wind and precipitation including very heavy snow on some California 14ers. This assumes the storm system stays on track.

Below, the visible satellite view from GOES-18 shows Hurricane Hilary. I drew on the projected path.

High Peak Impacts

Mount Whitney, CA.

Summit LevelGustsSnow
8/1940mphPM 1-3″
8/2060mph1FT+
8/2145mphAM 1-2″

Thunderbolt Peak, CA

Summit LevelGustsSnow
8/1925mphLate 1″
8/2030mph8-16″
8/2130mphAM 1-2″

Kings Peak, UT

Summit LevelGustsPrecip
8/19PM 35mphPM Rain
8/2060mphDry
8/2175mphPM

Grand Teton, WY

Summit LevelGustsSnow
8/1930mphPM 1-3″
8/2030mphPM R/S
8/2150mphDry

Boundary Peak, NV

Summit LevelGustsSnow
8/1930mphLate
8/2025mph6-14″
8/2145mphAM 1-3″

Granite Peak, MT

Summit LevelGustsPrecip
8/1935mphPM R/S
8/2050mphHeavy R/S
8/2160mphDrier

What’s Next? End of August and September Forecast Looks Active

Tomer’s Take: Persistent trough is king out West, and this might foreshadow what to expect this El Nino driven Winter. The seasonal Monsoon was three weeks late and intensity was disrupted. It was a victim of larger scale pattern. Lower atmospheric pressures dominate the West Coast through the end of August and then transition into the Intermountain West 9/1-9/15. Monsoonal moisture gets drawn into the flow as a contributor potentially through 9/15.

Let’s look at Hurricane Hilary. The atmospheric flow pulls this storm system into California and merges it with an area of low pressure currently off the West Coast.

Bath Water – SST’s

Below are 1-day sea surface temperature anomalies valid 8/7/2023 compared to 30-year climatology. Red/orange = warmer than normal. Sea surface temps remain warmer than normal near the Baja, PNW, Gulf, and Atlantic. This feeds tropical development and can affect regional flow.

Pattern Supports Lower Pressures

Below are forecast atmospheric pressure anomalies valid 8/19-8/20. Notice Hilary merging with an area of low pressure. The jet stream buckles and captures both.

Below is forecast total rainfall by late 8/21. Heavy rainfall and thunderstorms are likely from the Hilary/Low combo. An isolated 8-10 inch rainfall total possible in CA.

But, this moisture also hits ID, MT, SW UT, AZ, NV, and OR. Some Monsoonal moisture also gets drawn north and affects UT, CO, WY.

End of August

Below is the Global Forecast System forecast atmospheric pressure anomalies valid 8/29. The persistent trough remains off the West Coast. Also, notice another tropical system is forecast near the Baja.

This keeps some Monsoonal contribution in place for CO, WY, UT, NM.

September 1-15

Below, the Climate Forecast System moves the persistent trough eastward into the Intermountain West. The green represents above normal precipitation totals.

Areas in green receive their precipitation contribution from the Monsoon and an active jet stream.

This also indicates that the Monsoon stays later than normal. Typically, the Monsoon shuts down by September 1.

Below are forecast temperature anomalies for the same period (9/1-9/15). Heavier precipitation would keep temps cooler than normal (in blue) over the Intermountain West.

Bottom Line

Active Western pattern 8/20-9/10 with persistent Western Trough transitioning into the Rockies, Monsoonal moisture, and current/future tropical systems sucked into the flow (like Hilary).

In Colorado, September normally turns drier with the Monsoon shutting down, but that might not be the case this time around. WY, MT, UT, NM, AZ might be in the same boat.

Update: Ultra Season – Managing the Monsoon

Tomer’s Take: The Monsoon is late and weak. Moisture is slowly increasing across the desert southwest. Moisture increases in Colorado on 7/26 and ramps up into the first week of August. AZ, NM, NV, WY, UT, CO can all expect an increase in thunderstorms. The biggest Monsoon surge of the season so far is on tap for August 1-3.

Ultra Season

Hardrock was hot and dry. I’m still working with a few different athletes as they attempt to break FKT’s across CO, WY, MT. So far the Monsoon has been minimal, but that’s about to change on 7/26.

Current Setup

Water vapor satellite shows where the moisture is aloft in the atmosphere. Notice the high pressure and clockwise rotation. It’s starting to entrain Monsoonal moisture and transport it into the desert Southwest.

Late, Weak Monsoon

Normally, Monsoon season runs July 1 – August 31. Atmospheric winds turn southerly transporting in new moisture from the Gulf and Pacific. This moisture hits the Four Corners in waves. Timing the moisture surges is the critical forecasting part. This makes thunderstorms more likely early and late.

Here Comes the Monsoon

For the first time, atmospheric winds turn favorable for Monsoonal moisture. Below is the EPS jet stream forecast valid 8/2/2023.

Below is a forecast timeline comparison. It’s a precipitable water percent of normal forecast. Green/Blue = 100-300% of normal. The first image is valid 7/31, and the second image is valid 8/2. The surge on 8/2 is more significant.

Below is the forecast relative humidity at about 10,000ft valid 8/3. Forecast moisture is deep.

Bottom Line

Expect moisture to increase across AZ, NM, UT, CO, NV, and WY on/after 7/26 through the first week of August.

This will increase the chances for afternoon thunderstorms with heavy rain, frequent lightning, and hail. The storms could develop before Noon and last late into the night.

This will create smaller weather windows.