Powder Forecast – Friday, December 6th, 2024
Ted Schlaepfer CCM —- Mammoth Mountain WeatherGuy
Snowfall forecasts are valid at the Sesame snow course (Main Lodge) for the prior 24 hours.
**Snowfall forecast confidence ranges from very low (1) to very high (5)
Sat 12/7 = 0”
Sun 12/8 = 0”
Mon 12/9 = 0”
Tue 12/10 = 0”
Wed 12/11 = 0”
Thu 12/12 = 0 – 2”
Fri 12/13 = 0 – 4”
Sat – Mon 12/14 – 12/16 = 6 – 12”
December Snowfall = 0”
December Forecast = 40 – 60”
Detailed 4-day Snowfall Forecast:
Sat 12/7 through Tue 12/10 – No snowfall expected all days.
Forecast Summary:
Short Term (Days 1 – 4):
The current infrared satellite image (below) this afternoon shows a strong high-pressure ridge centered in the eastern Pacific stretching eastward into the interior West. This ridge will remain in place through Sunday for continued dry weather and mild temperatures for December.
An inside slider short-wave will move southward through the Great Basin on Monday (image below) and slightly colder temperatures and breezy winds will be the result. High pressure then rebuilds into mid-week.
Long Range (Days 5+):
The longer-range guidance favors dry weather ending around the end of next week or over the following weekend. It does not look like a major event right now, but certainly, enough snow could fall for multiple powder days, as the guidance suggests possibly two or three storms.
The latest ECM deterministic run now opens up the westerly flow into CA and moves the first short wave into CA on Wednesday night or early Thursday (image below). It follows that one with a splitting trough on Saturday (two images below) and then moves a stronger and wetter trough into Central/Northern California on Monday/Tuesday the following week (three images below).
The other models also have some trough passages, with the Canadian being the most similar to the ECM and the GFS the most different. But overall, the guidance is not in great agreement with the overall pattern and how exactly it will unfold, which is not uncommon with a 6-10 day forecast.
Unsurprisingly, the ECM model is also the wettest, with the series of storms showing around 2.5”-3.0” for the event (image below), and the ECM Artificial Intelligence Forecast System is similar (cover image). The GFS (two images below) is much drier and has less than an inch. The Canadian only goes out for 240 hours, so it doesn’t capture the entirety of the event, but its amounts through the period are higher than the GFS total.
Those differences between the models can also be applied to the ensemble means of the guidance. The ECM ensemble (image below) has about 1.5” liquid for the event while the GFS has about half that amount at 0.75” (two images below).
Overall, it looks like a good chance that the dry weather will come to an end with the best chance for powder days over the weekend and into the next week as the chance toward the middle/end of next week look rather iffy. I am thinking there is a decent chance for about a foot at Main with the best-case scenario two feet. It should start to come more into focus by the next update.
The fantasy range guidance says a positive Pacific North American (+PNA) will develop in the 11-15 day time frame with a deep trough in the Aleutians and a ridge along the West Coast (image below). That means a return to dry weather that may last through Christmas.
The next chance for snowfall and powder days might not be until the end of the month. Some of the models, like the GEFS (image below), are still saying the MJO will move into phase 7 and remain coherent by the end of the month and early January. As mentioned in previous posts, MJO analogs favor wet weather if that happens.
Hopefully the MJO will remain coherent/strong and continue to move eastward into phases 1 through 3 during January that are wetter for California. The just released ECM monthly forecast flipped from dry to average for January (image below) which is more consistent with the MJO sub-seasonal forcings that are now coming into focus. WG
