Powder Forecast –Friday December 8, 2017

Powder Forecast –Friday December 8th, 2017

Ted Schlaepfer CCM  —- Mammoth Mountain WeatherGuy

Forecast Summary:

   Dry with seasonably warm temperatures this weekend and through the middle part of next week with continued fair weather through mid-month, although colder temps are possible by the end of next week/following weekend.  Dry weather should then continue most of the third week of December with a chance for storms to return over last ten days or week of the month.

Next update Tuesday 12/12

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 12/9 = 0”
Sun 12/10 = 0”
Mon 12/11 = 0”
Tue 12/12 = 0”
Wed 12/13 = 0”
Thu 12/14 = 0”
Fri 12/15 = 0”
Sat – Mon 12/16 – 18 = 0”

December Snowfall = 0”
December Forecast = 20 – 35”

Detailed 5-day Snowfall Forecast:

Sat 12/9 thru Tue 12/12 — No snowfall expected all days.

Forecast Discussion:

Short Term:

The dry pattern continues through this weekend as a strong high pressure ridge (image below) remains planted along the West Coast blocking any storms well northward into Alaska.   The ridge will build stronger over CA too resulting in warmer temperatures this weekend with temps probably into the low/middle 50s at Main by Sunday.  December thaw for the lower part of the mountain with limited snow-making at night for Canyon/Eagle areas.

   The models are saying the ridge will hold firm through the middle part of next week (image below) for little change in the overall weather pattern through at least next Thursday.   Temps should get even warmer by next Wednesday and Thursday with spring conditions possible.

Long Range:

   Changes may finally start to occur by the following weekend. The deep trough in the East Coast will start to erode and lift northward and the models are suggesting that the longwave trough will retrograde westward.   This was hinted in the last update and the models are still suggesting it could happen.

   The longwave trough will still probably be not far enough westward for storms to have an over-water trajectory needed to advect  moisture into any extratropical cyclones with changes probably starting as inside slider type storms as shown by the latest ECM model (image below).   It moves it through east of the Sierra next Saturday for colder temps and probably increase northeast winds after its passage.   The GFS model has an even deeper inside slider type short wave trough for even colder temps and more wind.

   The longer range GEFS ensembles are then suggesting the longwave trough will continue to move westward as the East Coast trough peaks in strength and then lifts northward back into the Hudson Bay heading toward Christmas.   This suggests that the dry spell could end after the 20th with a storm possibly having enough over-water trajectory to produce low elevation rain and snow in the Sierra (image below).

   This could be the start of longer term favorable upper atmospheric changes in the teleconnection pattern heading into the end of the month and early January.   The fantasy range of the GFES shows the trough persisting along the interior West in split flow (image below), but more importantly, is favoring high latitude ridging to develop over the Aleutians (black box).

   A ridge or block in there region is usually results in a downstream trough for the West Coast and CA.   Or as some forecasters like to state, key atmospheric pressure indexes like the PNA (Pacific North America Pattern) will switch from positive to negative which is a generally a more favorable pattern for snowfall for the Sierra and Mammoth.

   Longer range climate models have picked up on this trend with the CFS model showing about average precipitation for the Sierra last part of December (image below) with the strongest below normal anomalies along the North Coast where average precipitation is the largest.   This suggests colder type storms that don’t have a subtropical tap—not that I believe such details on a three week forecast.

  Overall, longer range guidance is saying that the RRR (Ridiculously Resilient Ridge) won’t be all that resilient this time and should break down after the 20th and heading toward Christmas.  Even longer range climate models including the newly released ECM monthly model and the NMME climate model are showing a more active January with the NMME showing average precipitation for Mammoth and the ECM model slightly above normal.  Our patience will  be rewarded.  WG