Powder Forecast – Tuesday, December 16th, 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)
Wed 12/17 = 0”
Thu 12/18 = 0 “
Fri 12/19 = 0”
Sat 12/20 = 0”
Sun 12/21 = 0 – 2”
Mon 12/22 = 0”
Tue 12/23 = 0 – 2”
Wed – Fri 12/24 – 12/26 = 18 – 30”
December Snowfall = 0”
December Forecast = 40 – 55”
Detailed 4-day Snowfall Forecast:
Wed 12/17 through Fri 12/19 – No snowfall expected all days.
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 6” 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, with clouds moving southward into Mammoth. Only clouds are still expected from this passing weather system, which will move through the central Sierra on Wednesday morning.
High pressure will then rebuild over Central CA Thursday into Friday, before the next weather system moves into NorCal on Friday and Saturday (image below). This one will move a bit farther southward, and precipitation will likely reach Mammoth by Saturday.
Unfortunately, snow levels will be relatively high, generally in the 9000-9500 foot range, so rain is expected on the lower part of the mountain, and snow only from about McCoy to the Top, where a few inches of wet stuff are possible.
Long Range (Days 5+):
The longer-range guidance is continuing to trend more positively heading into Christmas, as a significant shift in the northern hemisphere teleconnection pattern takes place. This pattern looks to hold through the end of the year and into 2026.
The ECM model moves another short wave into CA on Sunday in the zonal flow off the Pacific (image below). There will probably be more rain for the lower part of the mountain and snow for only the Top again
The flow will probably lift northward on Sunday for some dry weather The ECM model is forecasting well over an inch (image below) for the weekend, so another six inches of wet type snow is possible for the Top for a total close to 10 inches of snowfall.
The models are in general agreement that a stronger storm will move into CA around Christmas Eve (ECM image below). It will probably move farther southward than previous storms.
The trough is well supported by the GFS ensemble (two images below), with the ECM EPS showing a chance it may stall off the coast before landfall (three images below). Thus, the details are still uncertain.
The most significant uncertainty is how quickly snow levels will fall, with the ECM model not pushing them below 7000 feet until Wednesday PM/evening. Amounts from the system look impressive, as the GFS (image below) shows over 5” of liquid, a nd the ECM model around 4” (two images below).
It’s been over a week since the forecast changed. The current forecast follows the ECM EPS that has about 4-5” of liquid for the event (image below). That model also keeps snow levels around 8K or higher until Wednesday night, when it lowers them to 7. K Thus, there will be a lot of snowfall up Top. Still, snow ratios may be relatively low at Main with the Sierra cement, and amounts may be only a couple of feet. Not great powder skiing snow, but great base snow.
Both the ECM EPS and GFS ensembles (image below) keep the longwave trough positioned along the West Coast through the end of the year. Hopefully, the jet stream (purple arrow) will be far enough southward for storms/cold air to make it southward into Mammoth. Current guidance says it will be closed.
The fantasy range forecast keeps the storm train going through the first two weeks of January. Both models (images below) show above-normal precipitation for the first week and slightly above-normalcipitation for the second week. It looks like January could be a good month, at least the first half. WG.
