Powder Forecast – Tuesday December 20th, 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)
Wed 12/21 = 0”
Thu 12/22 = 0”
Fri 12/23 = 0”
Sat 12/24 = 0”
Sun 12/25 = 0”
Mon 12/26 = 0”
Tue 12/27 = 0”
Wed – Fri 12/28 – 12/30 = 10 – 22”
December Snowfall = 77”
December Forecast = 90 – 110”
Detailed 4-day Snowfall Forecast:
Wed 12/21 through Sat 12/24 – No snowfall expected all days.
Short Term (Days 1 – 4):
The current infrared satellite image (below) shows a weak weather system situated along the northern CA coast and just some passing clouds elsewhere. High pressure off the coast will build into the state tomorrow.
The high pressure ridge will remain in place on Thursday (image below) for continued dry weather before another weak weather system produces some rain across NorCal Friday and just passing clouds for Mammoth.
High pressure will then build more strongly over the Holiday weekend with the ridge peaking in strength on Christmas Day (image below) for fair weather and unseasonably mild temperatures. Temps up top could get into the upper 30s/low 40s with low to mid-50s possible at Main.
Long Range (Days 5+)
The longer-range guidance has generally trended much more favorable for snowfall since the last update with a series of storms now possible for the last part of the month and into early January.
The ECM (image below) and other models agree that the first chance for snowfall will be around Tuesday next week. For the 12z runs, the GFS and ECM were similar while the Canadian is a bit stronger/wetter.
While the 12z run was promising, the ECM EPS (image below) is farther northward with the short-wave versus the operational models. It is showing about half of the precipitation amounts that the operational models are forecasting. Thus, a little caution is still needed to see if the trough will dig far enough southward for significant snowfall.
Models then move another short-wave trough off the Pacific on Wednesday and into Thursday (image below) for another potential round of snowfall that may continue into Friday. Another concern is snow levels as they may rise to near Main Lodge by the end of the week under the zonal flow off the Pacific that may contain an Atmospheric River (AR).
Overall, the QPF from the 12z runs of the GFS (image below) and ECM (two images below) is around 4” with the wetter Canadian model showing around 6”. Current forecast is a bit more conservative and a blend of the operational models and ECM EPS that has around 2”. Thus, the forecast has at least 12 inches of base type snowfall and maybe close to two feet by the end of the 10-day period.
The longer range ensembles favor another short-wave to move off the Pacific around New Years’ Eve with the ECM model (image below) only slightly faster and more zonal than the GFS (two images below). This would be another warmer type storm with high snow levels, although that detail is too far out in time to call right now.
The fantasy range keeps the storm train going over the first part of 2023 with the ECM EPS (image below) fairly bullish about a deep trough along the West Coast and a zonal jet into Central CA. That could potentially produce an even stronger storm system.
Confidence in the pattern change is decent for such a long time horizon and that is because it looks like the pattern change is due to forcing from the tropics and the MJO in particular. The models are forecasting an MJO event to occur at the end of the month/early January with the signal emerging in phase 5 and moving eastward into phases 6 and 7 in early January (image below).
While that signal is most bullish about warm temperatures across the eastern US, there is also a wet signal for CA during the first week of the month. Thus, the ECM EPS (image below) that is showing over 5” liquid for Mammoth in the 15-day period may be realized. Maybe even the 12z run of the GFS that has over 12” liquid (two images below) for the same time period. Fingers crossed. WG