Powder Forecast – Friday, December 13th, 2024
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 12/14 = 5 – 7” (H20 = 0.50” – 0.75”)**3
Sun 12/15 = 9 – 12” (H20 = 0.90” – 1.25”)**3
Mon 12/16 = 0”
Tue 12/17 = 0 – trace”
Wed 12/18 = 0”
Thu 12/19 = 0”
Fri 12/20 = 0”
Sat – Mon 12/21 – 12/23 = 0 – 2”
December Snowfall = 9”
December Forecast = 40 – 60”
Detailed 4-day Snowfall Forecast:
Sat 12/14 – Light to moderate snowfall during the morning turns heavy during the afternoon before tapering off late PM and ending evening. Very strong winds during the morning/afternoon. Accumulations 9 – 12” by Sunday AM at Main, 12”+ up top
Sun 12/15 – Tue 12/17 – No snowfall expected for all days except for a chance for flurries or light snow showers Monday night.
Forecast Summary:
Short Term (Days 1 – 4):
The current infrared satellite image (below) this afternoon shows a short-wave ridge over Southern California and a deep low-pressure system off the Pacific Northwest coast, with a frontal boundary stretching southwestward into the eastern Pacific. A developing wave or low-pressure system on the southern boundary will stall the front’s southern movement late tonight and early tomorrow.
The upper-level short wave associated with the developing wave will move inland Saturday morning (image below) and into Mammoth during the afternoon. Moisture upslope southwest flow ahead of the cyclogenesis will increase snowfall in Mammoth overnight with a brief decrease or lull possible tomorrow morning before heavy snowfall occurs during the early afternoon.
The snowfall will taper off rather quickly during the late afternoon and should end in the evening, right around or just before the Night of Lights at Canyon starts.
The ECM model is the outlier, with the QPF at only around 0.90” (image below). The GFS (two images below), Canadian (three images below), and the National Blend of Models (four images below) all show over an inch and around 1.5-2.0”.
The forecast follows the wetter guidance and is calling for about 6” at Main for opening Saturday, followed by another 9-12” during the day. It doesn’t look like Saturday will be a great riders of the storm day, as very strong winds during operations will probably shut down most of the mountain. But Sunday should be an excellent bluebird powder day; make sure to get out there if you can.
The models agree that the next weather system (image below) will stay too far northward for any meaningful snowfall in Mammoth.
The ECM model is dry (image below), and the GFS only has trace amounts (two images below). That is similar to the ECM ensemble mean (3 images below). It will probably just result in passing clouds and breezy winds (wind buff up top).
Long Range (Days 5+):
The longer-range guidance favors dry weather through most of next week and only chances for snowfall through the end of 2024. Even though the guidance is not bullish on any storm events, the MJO remains active and has not been predicted accurately lately, so quick changes in the models would not be surprising.
A high-pressure ridge will build into the state mid-week (image below) before a weakening short-wave attempts to bust through it at the end of the week or early weekend (two images below).
It will probably stay too far northward for any significant snowfall in Mammoth, with the ECM ensemble only showing about a tenth of an inch of precipitation (image below). However, it is still over a week out, so hopefully, that will change.
The latest 12Z ECM does try to move a stronger short-wave trough into the state just before Christmas (image below), and its QPF output (two images below) would result in significant snowfall.
However, that solution is not well supported by the ECM ensembles, with the mean (image below) having the position of the trough much farther northward versus the deterministic run. QPF does show enough for low-end powder conditions (two images below), but that is a product of a handful of ensembles that share the 12z deterministic solution. The GFS doesn’t share that solution, with only a very weak wave moving into the state.
Hopefully, the trend will be wetter as we get closer, and the models will also get a better handle on the MJO. They have been too slow with the eastward progression of the signal, and if it moves faster into phases 6 and 7 toward the end of the month, then the guidance should trend wetter. The latest CFS does have another good storm event for central and northern CA over the last week of the month, consistent with its forecast of the MJO moving into phase 6/7. WG
