Powder Forecast – Friday, December 19th, 2025
Ted Schlaepfer CCM —- Mammoth Mountain WeatherGuy
Snowfall forecasts are valid at the Sesame snow course (Main Lodge) for the prior 24 hours as reported in the 6-7 AM morning snow report.
**Snowfall forecast confidence ranges from very low (1) to very high (5)
Sat 12/20 = 0 – 1” (H20 = 0.15” – 0.25”) **4
Sun 12/21 = 0 – 1” (H20 = 0.25” – 0.35”) **4
Mon 12/22 = 1 – 2” (H20 = 0.35” – 0.50”) **4
Tue 12/23 = 0”
Wed 12/24 = 6 – 10”
Thu 12/25 = 25 – 35”
Fri 12/26 = 20 – 30”
Sat – Mon 12/27 – 12/29 = 3 – 6”
December Snowfall = 0”
December Forecast = 45 – 65”
Detailed 4-day Snowfall Forecast:
Sat 12/20 – Chance for rain in the morning with rain/snow likely during the afternoon and night. Snow levels around 9000-9500 feet. Little or no accumulation at Main, up to 2” at the Top.
Sun 12/21 – Rain/snow likely during the morning, tapering off during the afternoon, Snow levels around 9000-9500 feet—little or no accumulation at Main, up to 4” at the Top.
Mon 12/22 – Chance for rain/snow in the morning, then probably dry. Snow levels around 8500-9000 feet. Little to an inch accumulation at Main, up to 6” at the Top.
Tue 12/23 – Dry during the day, then heavy snowfall develops overnight. Snow levels around 7000-7500 feet. Accumulation at Main 6-10” by Wednesday AM, up to 12” at the Top.
Forecast Summary:
Short Term (Days 1 – 4):
The current infrared satellite image (below) this afternoon shows a frontal system moving into NorCal, and the tail end of the front will move into Mammoth late tonight and early tomorrow, with some rain/snow showers. Snow levels will be around 9000 feet, and not much, if any, accumulation is expected.
The plume of moisture well off the coast, associated with another low-pressure system, will then move into the state tomorrow and S. day. The models (image below) show decent southwest flow into the east, and that flow will have an embedded atmospheric river (two images below).
Heavy precipitation is expected north of Mammoth over the weekend and into Monday as a result, with the ECM (image below) showing less southward into Mammoth versus the GFS model (two images below) that has about three times as much and around 3” of liquid. The ECM EPS (three images below) is similar to the latest ECM above.
Unfortunately, snow levels will mostly remain above 9000 feet through the weekend. It will be a mix of rain and snow for the mountain. Only the Top will see snow the whole time, with Main probably seeing rain most of the time, with snow levels maybe getting down to 8500 Sunday night. Thus, no meaningful accumulation is expected at Main this weekend.
The jet stream and AR will lift northward on Monday afternoon and continue into Tuesday, bringing a period of dry weather. Then the main event will begin on Tuesday night and continue into Christmas Eve.
Long Range (Days 5+):
The longer-range guidance shows a significant snowstorm for the middle and end of next week, and it hints that the pattern will reload again during early January. There are indications it could keep going into mid-January.
The model guidance has generally agreed that a deep upper-level longwave trough will develop along the West Coast by Christmas Eve (image below), with the parent trough moving ashore on Christmas (two images below) for two rounds of heavy snowfall. This pattern is well supported by the ECM EPS (see the three images below).
The 12z run of the ECM model is showing around 6” liquid for the period (image below). The GFS is showing even more at around 8-9” (two images below) Forecast leans toward the ECM EPS (three images below) that has about 5-6” liquid It is still about five days out, so the forecast will likely change.
The good news is that snow levels should come down to around 7000 feet by Christmas Eve and then lower to 5500-6000 feet by Christmas and next Friday Two rounds of heavy Sierra cement are expected with lingering snowfall through Friday Right now, it looks like two to three feet on Wednesday followed by another two feet Thursday into Friday The Top will probably get around six feet of snowfall The system exits eastward on Saturday (image below) and dry weather should return for the weekend.
The longer-range guidance reforms the longwave trough along the West Coast to start 2026 (image below) and suggests enough precipitation and snowfall could fall for powder conditions. The ECM EPS (two images below) shows about an inch of precipitation at the back end of the period, which might be just the start of the next storm cycle.
Both the ECM EPS (images below) and the GFS long-range forecast show generally above-normal precipitation for the first half of January, especially the early part. With a nice base likely in place by then, let the powder days begin, WG.
