Powder Forecast –Tuesday, April 20th, 2021
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 4/21 = ~1”
Thu 4/22 = trace – 2”
Fri 4/23 = 0”
Sat 4/24 = 0”
Sun 4/25 = 0 – 1”
Mon 4/26 = 6 – 10”
Tue 4/27 = 3 – 6”
Wed – Fri 4/28 – 4/30 = 0”
April Snowfall = 2”
April Forecast = 10 – 20”
Detailed 4-day Snowfall Forecast:
Wed 4/21 – After some early AM light snowfall, more snow showers are possible through the afternoon hours before ending during the evening. Accumulations trace – 2”.
Thu 4/22 – Dry through the early afternoon, then a chance for a late afternoon/evening snow shower. No accumulation expected.
Fri 4/23 and Sat 4/24 – No snowfall expected on both days.
Short Term (Days 1 – 4):
The infrared satellite image (below) this afternoon shows an upper-level low-pressure system positioned across NorCal where showers and thunderstorms are currently developing across the mountains.
That weather system will slide southward by early tomorrow (image below) to a position over the Central Sierra before moving southward and mostly out of the area by Thursday.
Models are depicting some light snowfall developing late tonight and early tomorrow for a couple of hours, and then snow showers during the late morning and into the evening hours. Not expecting a lot of accumulation and no more than a couple of inches as QPF from the guidance is around 0.10”-0.20” (image below). Snow levels will be around 7000 feet tomorrow morning, then around 8500-9000 feet tomorrow afternoon, so it is not a cold storm.
There will be a chance for a lingering shower late afternoon Thursday, otherwise, high pressure builds into the region Friday (image below) and should hold through Saturday. However, it looks like west winds will increase Saturday during the day and could get gusty.
Long Range (Days 5+):
The longer-range guidance has now trended much more favorable for a late-season surprise snowstorm and spring powder day(s).
The latest 12Z ECM model moves a rather deep upper-level trough into CA (image below) early Sunday and the cold front into Mammoth during the day for increasing snowfall. It keeps the upper-level trough off the coast through Monday and doesn’t swing it inland until early Tuesday (image below) for continued snowfall. That model is showing over 2” liquid and almost 2 feet of snowfall.
The other models move the trough through CA faster on Sunday and Monday by about 12 hours or so with a shorter period of southwest jet stream flow associated with the storm, and thus lesser snowfall amounts. Both the GFS (image below) and the Canadian (two images below) models have about 1.25” and may be up to a foot.
The good news is the GFS ensemble mean has good support for a deep upper-level trough (image below) but is not bullish on big amounts yet as it is only showing about 0.50” of liquid (two images below) or about six inches of snowfall. Overall, it is looking good for a storm and at least low-end powder conditions on Sunday and/or Monday, but the details still need to be sorted out.
The longer-range GFS ensemble mean moves another trough (image below) well north of Mammoth around the middle part of next week. The ECM though, has it farther southward, so there is another chance for snowfall, but probably not a big storm.
The fantasy range guidance then develops rather typical spring weather by the following weekend (image below) and beginning of May with a flat ridge of high pressure over California. May powder days are generally uncommon, so the storm this Sunday/Monday could be it for the season. WG
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