Powder Forecast – Friday December 9th, 2022
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 12/10 = 0”
Sun 12/11 = 32 – 40” (H20 = 3.50” – 4.25”)**4
Mon 12/12 = 5 – 10” (H20 = 0.50” – 1.00”)**3
Tue 12/13 = 0”
Wed 12/14 = 0”
Thu 12/15 = 0 – 3”
Fri 12/16 = 0 – 6”
Sat – Mon 12/17 – 12/19 = 3 – 12”
December Snowfall = 48”
December Forecast = 95 – 110”
Detailed 4-day Snowfall Forecast:
Sat 12/10 – Snowfall develops during the morning hours, then becomes heavy by the late afternoon and overnight hours. Strong winds likely develop during the day and peak overnight when white-out conditions are expected. Accumulations 32 – 40” Main Lodge, up to 48” up top.
Sun 12/11 – Heavy snowfall and strong winds during the early morning, decreasing by the afternoon and evening, tapering off overnight. Accumulations 5 – 10” at Main by Monday AM, up to a foot up top.
Mon 12/12 – A chance for light snowfall during the morning with flurries during the afternoon. No accumulation expected.
Tue 12/13 – No snowfall expected.
Short Term (Days 1 – 4):
The current infrared satellite image (below) shows a developing storm system moving into the eastern Pacific this afternoon and that storm will turn into the classic winter storm for Mammoth starting tomorrow.
The ECM model moves the upper-level trough southward early tomorrow (image below) and then southward through the Sierra on early Sunday (two images below). The storm will be back by a strong polar jet stream (blue arrow) that will drive a robust cold front southward through CA. It will exit out of the area on Monday (three images below)
The storm will also tap into subtropical moisture as it moves southward into the state tonight and early tomorrow. The ECM model is showing a precipitable water plume (image below) of almost 1.5” of integrated water vapor centered along the Central Coast eastward into the Sierra on Saturday afternoon.
Due to the strong low/middle level winds along trajectory of the moisture plume, it qualifies as a weak to borderline moderate Atmospheric River (AR) (image below). According to the chart, the AR peaks in intensity Saturday evening and night.
The models (Canadian below) drive that moisture-laden front southward through Central CA tomorrow afternoon and night. That is when the heaviest snowfall and strongest winds are expected. Snowfall rates along with the strong winds will result in white-out or blizzard conditions in town overnight into early Sunday.
Since it is an AR, the storm is not a cold one. Snow levels with the bulk of the snowfall will be around 6500 feet before snow levels fall Sunday to near 4500 feet as the snowfall is tapering off. Snow levels will lower further on Sunday night, but not much more precipitation is expected. Thus, this will mostly be base-type snowfall with a layer of colder type snowfall on top at the end.
Model QPF for the storm is almost 6” per the Canadian model (image below) with the GFS (two images below) also quite wet at over 5” while the ECM (three images) is the lowest again at around 4” liquid. I think the ECM is a bit too low, while the others are a bit too high.
Overall, at least 3 feet of snowfall looks good for Main with possibly up to 4 feet or slightly more with most of the snowfall falling by Sunday morning. The top will probably get between 4-5 feet with the event. ECM model is showing copious amounts of snowfall for the Sierra range (image below) Strong winds will likely cause lift holds on both days with Sunday likely a slow opener due to the strong winds. Winds on Sunday should die off during the morning hours somewhat quickly though.
There is a chance for lingering light snow Monday morning with flurries possible in the afternoon. Otherwise, dry weather returns early next week and should continue through Tuesday and maybe Wednesday.
Long Range (Days 5+)
The longer-range guidance is still mixed about the pattern for the latter part of next week and into the following weekend before favoring a dry period to develop over the following week, again pushed back by a few days. This year so far has been the opposite of previous drought seasons when it always seemed that the snow chances would always disappear as we got closer in time. Now the dry periods seem to keep disappearing. No complaints here, hope that trend continues.
The 12z operational runs of the ECM (image below) and Canadian (two images below) models both keep a short-wave ridge over CA through at least Thursday or Friday next week resulting in dry weather. They both show a trough remaining well off the coast.
However, the GFS model (image below) has that trough of low pressure much closer to the coast by mid/end of next week and brings snow back to Mammoth on Wednesday and Thursday. It brings a bit more in over the weekend and QPF from the model (two images below) is just under an inch for the mountain.
The GFS ensemble (image below) and the ECMWF EPS (two images below) also are not in great agreement, although both do show a low-pressure trough over CA. The GFS is just deeper with the low and that would make a difference with any potential snowfall. Current forecast follows a blend of the models and has snowfall chances increasing toward the end of next week and through the following weekend, although it is a low confidence forecast. It could go either way.
Beyond that, the fantasy range models are in agreement again that the long-wave trough will shift eastward by the middle part of the following week (image below). That would result in dry weather through Christmas or slightly longer.
Super long range ECM EPS climate model is still favoring storms to return over the latter part of the month with the model showing above normal precipitation (image below). That is followed by a period of average precipitation into early January (two images below). Average weekly snowfall in January is over a foot. Fingers crossed. WG