Powder Forecast – Friday, December 6^th, 2019

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 12/7 = 1 – 2” (H20 = 0.15” -0.25”)**4
Sun 12/8 = 16 – 19” (H20 = 1.75” -2.00”)**4
Mon 12/9 = 0 – 2” (H20 = 0.05” -0.15”)**4
Tue 12/10 = 0”
Wed 12/11 = 0”
Thu 12/12 = 0– 1”
Fri 12/13 = 0”
Sat-Mon 12/14– 12/16 = 2 – 8”

December Snowfall = 26”
December Forecast = 60 – 80”

Detailed 4-day Snowfall Forecast:

Sat 12/7 — Moderate to heavy snowfall during the morning with snowfall continuing at times into the evening before becoming heavier again overnight into Sunday morning.  Accumulations 16– 19” by Sun AM with up 24” up top

Sun 12/8 —Heavier snowfall ends during the early morning with scattered snow showers during the day.  Accumulations 0– 2” by Mon AM

Mon and Tue 12/9 and 12/10 —No snowfall expected both days

Forecast Summary:

Short Term (Days 1 – 4):

  Satellite imagery this afternoon (image below) shows a moderately deep low-pressure system well off the California coast and an associated cold front moving into NorCal.  That front is forecast to move southeastward through Central California overnight and into Mammoth early Saturday.

   The ECM model (image below) positions the upper level low just off the CA coast early tomorrow morning with the moist southern branch of the jet stream (purple arrow) aimed right into the Sierra.  So the system will have plenty of moisture to produce good amounts of snowfall.

   The snowfall with the cold front will start early Saturday morning and increase during the early and mid-morning hours before decreasing in intensity during the afternoon and evening.  Models (ECM below) then shift the upper-level low-pressure system southward by early Sunday.  The post-frontal trough (dashed yellow line in the satellite image above) will then produce another period of heavier snowfall overnight Saturday and into early Sunday ending by the time the lifts open.

   Models are generally showing between 2.00-2.50″ of liquid that is lower from the last post.  GFS (image below) has a little over 2” while the Canadian has closer to 2.5” (two images below) and the ECM has about 2” liquid.  This will not be a cold storm and snow ratios will be around 9-10”:1” or lower.  This will be Sierra cement base snow.

   High pressure will then build into Mammoth and California in the wake of the storm system and hold through early next week for a return to dry weather. Should be nice weather Monday and Tuesday with just some high clouds by Tuesday afternoon

Long Range (Days 5+):

    A weak splitting trough will move through the high-pressure ridge around Wednesday next week (image below) for mostly cloudy skies and a chance for flurries.  There could also be some breezier SW winds for wind buff conditions on the upper part of the mountain.

   The ridge of high pressure should then hold into the following weekend before there is a chance for the passage of an upper-level trough around late Saturday or early Sunday of that weekend (image below).  The ECM model is certainly the strongest at this moment with 6”+ of snowfall.

   The GFS has some snowfall on Saturday evening but washes the trough out on landfall.  GFS ensembles (image below) are rather mixed with the solutions.  About a third show a favorable trough in the right location with the others having the jet stream flow too far north for any snowfall.  Right now looks like about a 30-40% it could happen.   The next chance for snowfall would be around Dec 17-18^th and again around the 20^th.  WG