September Update - Winter 25/26 Season Snowfall Outlook Data

23d (edited) • Weather

September 5th, 2025 – ECMWF Seasonal Model Update

Today’s ECMWF seasonal run keeps the weak La Niña in play a bit longer. Instead of fading quickly, the signal now holds through at least January, with neutral conditions not expected until mid to late February.

Here’s what the maps are showing:

Nov–Dec–Jan: Greens light up across northern California and into the Sierra — often a sign of more storm action and a better shot at building early season snowpack.
Jan–Feb–Mar: More green, though a shade lighter. That’s still a positive signal for a full season’s worth of snowfall. Yes, this far out we’re in “fantasy land,” but green is always the color we want to see.

Take a look at the ECMWF maps below — green shades mark wetter than normal trends, while brown shades point to drier conditions.

September runs are a key checkpoint. If the Sierra stays painted green again in October’s update, confidence builds for a solid and steady winter. For now, it’s encouraging to see the signal lean our way.

— Snowman

👉 Follow the Mammoth Weather Story here: https://www.mammothsnowman.com/mammoth-mountain-weather-forecast/

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