Powder Forecast – Tuesday, December 10^th, 2024

from 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.

Sesame Snow Course

**Snowfall forecast confidence ranges from very low (1) to very high (5)

Wed 12/11 = 0”
Thu 12/12 = 0 – 1”
Fri 12/13 = 3 – 5” (H20 = 0.35” – 0.50”)**3
Sat 12/14 = 1 – 3”
Sun 12/15 = 15 – 20” (H20 = 1.50” – 2.00”)**2
Mon 12/16 = 0”
Tue 12/17 = 2 – 5”
Wed – Fri 12/18 – 12/20 = 0”

December Snowfall = 0”
December Forecast = 40 – 60”

Detailed 4-day Snowfall Forecast:

Wed 12/11 – No snowfall expected during the day/evening, snowfall develops late at night. Accumulations 0 – 1” by Thursday AM at Main.

Thu 12/12 – Moderate snowfall is expected during the day, tapering off in the afternoon and ending at night. Accumulations 3 – 5” by Friday AM at Main, 6”+ up top.

Fri 12/13 – Dry during the morning, then flurries are possible during the afternoon, and light snowfall overnight.  Accumulations 1- 3” by Saturday AM.

Sat 12/14 –  Moderate to heavy snowfall should reach Mammoth by Saturday afternoon and continue Saturday night before ending Sunday morning. Accumulations 15 – 20” by Sunday AM at Main, 24” up top

Forecast Summary:

Short Term (Days 1 – 4):

  This afternoon, the current infrared satellite image (below) shows a high-pressure ridge over California and high clouds moving into the state ahead of a weakening weather system. Another weather system moving into the eastern Pacific will bring some snowfall on Thursday.

   The models (ECM below) move a short-wave trough into CA on early Thursday and a front southward through the Sierra. It will move through rather quickly, and the jet stream is rather weak and not oriented southwestward long enough for a good spillover into the eastern Sierra.

  The models differ a bit in the precipitation forecast. The ECM is the driest (image below) at around 0.25”, and the GFS is the wettest (two images below) at about half an inch. The National Blend of Models (three images below) is about a third of an inch between the two.

  The forecast follows the NBM/GFS for the most part, with snowfall starting early Thursday and peaking during the morning hours before decreasing during the afternoon and ending at night. Just enough should fall for at least low-end powder conditions by midday Thursday, with powder conditions likely up top on Friday morning.

  Friday, there may be some flurries during the afternoon and then light snowfall overnight ahead of the next storm. This stronger storm will move into NorCal later Friday and then Central CA and Mammoth during the day Saturday and Saturday night. 

The ECM model (image below) forecasts a deep trough with moderate to strong southwest flow into the Sierra for good spill-over into the Mammoth/eastern Sierra region.

 Moderate to heavy snowfall should reach Mammoth by Saturday afternoon and continue Saturday night before ending Sunday morning. The models generally favor over an inch of liquid precipitation, with the ECM and GFS both forecasting (images below) around 1.5” or slightly more.

  Due to the deep trough and strong jet stream, the forecast leans toward the wetter side. A foot or more is expected at Main and possibly around two feet up top. There may be enough snowfall by Saturday morning/midday for powder storm riding on Saturday, with Sunday being a powder day mountain-wide.

Long Range (Days 5+):

   The longer-range guidance suggests a chance for an additional storm early next week and then again toward the end of next week before dry weather returns for the Christmas time frame.  The next chance for snowfall might not be until the end of the year or early 2025.

  The next potential storm is forecast to move into the state on Monday into Tuesday. The latest run of the ECM model (image below) weakens it and keeps it farther north when it moves ashore. The GFS model (two images below) differs and is deeper/farther southward with the trough.

  Model QPF shows the expected differences with the GFS, the wetter model (image below) at around 0.75” and the ECM (two images below) much drier at less than a tenth of an inch. The ECM EPS is only slightly wetter at about two-tenths (three images below). Hopefully, the forecast will trend wetter, but right now, it only favors a couple to a few inches of snowfall.

  Dry weather is then favored for mid-week next week, with the guidance suggesting another trough may move into the West Coast toward the end of next week or early the following weekend (image below).  It is currently favored to stay in NorCal, but many of the ensembles have it farther southward, reflected by about an inch in the quantitative precipitation forecast by the ECM ensemble mean (two images below). If it does move southward, it could be quite wet, as there is a strong jet stream backing it, fingers crossed.

   As mentioned in previous posts, if the MJO moves into phase 7 by the end of the month and/or early January, then analogs favor storminess for central and northern California.  None of the guidance is showing anything yet, although the CFS is continuing to trend wetter for January.  Fingers crossed.  WG