Powder Forecast – Tuesday, December 9th, 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 12/10 = 0”
Thu 12/11 = 0”
Fri 12/12 = 0”
Sat 12/13 = 0”
Sun 12/14 = 0”
Mon 12/15 = 0”
Tue 12/16 = 0”
Wed – Fri 12/17 – 12/19 = 0 – 6”
December Snowfall = 0”
December Forecast = 30 – 50”
Detailed 4-day Snowfall Forecast:
Wed 12/10 through Sat 12/13 – No snowfall expected all days.
Forecast Summary:
Short Term (Days 1 – 4):
The current infrared satellite image (below) this afternoon shows high pressure parked off the CA coast, with storm systems riding up and over the ridge into the Pacific Northwest and British Columbia. The ridge (image below) will remain mostly in place through the upcoming weekend for continued fair/dry weather and seasonably mild temperatures.
Long Range (Days 5+):
The longer-range guidance is trending more positive after mid-month, suggesting at least a shift in the broader teleconnection pattern. More significant positive changes could lie ahead over the last part of the month.
The latest 12z deterministic run of the ECMWF keeps the high-pressure ridge (image below) mostly in place through the end of next week, with the jet stream well to the north, supporting continued dry weather. The Canadian deterministic model run is similar, and the GFS is drier for the state.
However, the ECMWF EPS favors a zonal flow along the West Coast next week (image below), with the southern branch of the jet stream (purple arrow) centered along the California/Oregon border. That position is too far north for significant precipitation in Mammoth and also suggests high snow levels with any precipitation that does make it farther southward.
A little bump southward with the jet stream, and that could change. Many ECM ensembles show a more favorable solution evident on the precipitation forecast for next week (image below). The ensemble mean shows about an inch of liquid for Mammoth, with most of that falling around Tuesday next week. However, that model also shows snow levels above 8500-9000 feet. It is still too far out to know the details, especially since the deterministic runs do not show snowfall.
The overall teleconnection pattern across North America is expected to change by the end of next week and through the Christmas time frame. The models suggest the trough in the East will fill, and zonal flow will develop along the West Coast as a deep trough replaces a ridge over British Columbia/eastern Alaska. Both the GFS (image below) and ECM (two images below) are showing this pattern, and the key will be how strong the ridge in the Aleutians will be; a stronger high will push the jet stream farther southward.
The ECM has a little stronger zonal flow and is more bullish about precipitation southward into CA, showing around 2” for the period (image below). The Canadian ensemble (two images below) is similar,, while the GFS ensembleshowsg about half the amounts of the other models. Regardless, it is a favorable trend after a very dry start to the month.
The fantasy range guidance is favoring above normal (GFS extended below) or slightly above normal precipitation (ECM two images below) for the last week of the month. Both models show a similar pattern of activity for the first week of January. Just a bit more waiting until powder days are here. WG
