Powder Forecast –Friday December 15th, 2017

Ted Schlaepfer CCM  —- Mammoth Mountain WeatherGuy

Forecast Summary:

   Mostly cloudy, windy, colder with flurries/light snow showers Saturday ending evening followed by continued gusty north winds Sunday, then lighter winds Monday.  Dry weather continues Tuesday, then there is a chance for light snow next Wednesday followed by more gusty north winds end of the week.  Dry weather may then last until just before the end of the month with snow chance continuing through early January.

Next update Tuesday 12/19

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 12/16 = 0 – trace”
Sun 12/17 = 0 – trace”
Mon 12/18 = 0”
Tue 12/19 = 0”
Wed 12/20 = 0”
Thu 12/21 = 1 – 4” **2
Fri 12/22 = 0”
Sat – Mon 12/23 – 25 = 0”

December Snowfall = 0”
December Forecast = 15 – 30”
Detailed 5-day Snowfall Forecast:

Sat 12/16 — Light snow/flurries possible by early Saturday and during the day.   Maybe an inch accumulation.

Sun 12/17 thru Tue 12/19 — No snowfall expected all days.

Forecast Discussion:

Short Term:

Dry weather should come to a brief end Saturday as an inside slider type short wave trough digs a bit farther toward the coast during its passage southward Saturday (image below).  Light snow showers or flurries are possible by early Saturday along with colder temperatures and may continue at times through the afternoon.  No meaningful accumulation is expected, but gusty north to northeast should be with continued gusty winds Sunday.

   High pressure rebuilds by Monday (image below) for continued dry weather and lighter winds.   That ridge of high pressure should hold through Tuesday before there is another chance for light snow Wednesday.

Long Range:

   Model consensus has a stronger short wave trough also taking an inside slider type direction through CA and the Sierra next Wednesday (image below), and if you remember from the last post, models were all over the place with solutions regarding this low last week.   They have settled on this solution for now that would produce mostly colder temperatures and wind along with some light snowfall.

   None of the models are currently showing enough snowfall for powder conditions with the latest GFS dry, Canadian showing maybe an inch, while the ECM shows a few inches.   The ECM mean is generally favored right now and it has only a couple inches. The low pressure system is just tracking too far inland to advect needed moisture to produce significant snowfall.

   A few of the ECM ensembles are showing a more favorable direction for the short wave passage off the Pacific to produce snowfall and the event date is still 5-6 days out, so it is certainly likely that the end result will be different as the low could take a more (less) favorable track through CA for higher (lower) snowfall amounts, including a chance for nothing if it moves farther east.   On the bright side, the current low for Saturday was projected to move southward through the Great Basin on the Tuesday update, and is now moving through CA farther west.

   Let’s hope that it moves farther westward on its track through CA, because longer range guidance is favoring sustained upper level West Coast ridging again through at least Christmas for dry conditions.    That upper low is expected to cut-off from the jet over the Gulf of California to basically form an omega block  along the West Coast.   Those blocks are stable and usually last five days to a week.

   That is what is now being favored by the longer range model ensemble suites with dry weather likely through Christmas.  That is also supported by tropical forcing as the MJO will be in phase 8 according to the ECM model (image below).   That strongly correlates to troughing (colder temps) along the East Coast and dry conditions along the West Coast which is exactly what the ensembles are favoring.

    The good news in all of this bad news is that the models are now showing that the MJO could finally move out of the western Pacific (phases 6 and 7) and into phase 1 by the end of the month.   Phase 1 supports West Coast troughing (colder temps) along with wet conditions both in December and January.  That is our best bet to end the dry spell in a more significant way.

   This is what the climate models are probably picking up on.  Both the CFS and ECM favor some sort of storm activity end of the month and through early January.   The CFS shows a weak breakthrough of the westerlies (image below) as the block moves into a better position in northern Alaska.  It keeps the westerly jet active into the second week of January (image below), although it is showing anticyclonic flow increasing over southern extension of the jet, hinting at ridging heading into mid-month.  Latest ECM keeps a trough along the West Coast.

    Both models are showing above normal precipitation over that period with the CFS more bullish (image below) than the ECM.  The CFS keeps it going through the first 10 days of January (two image below) and the latest ECM has cold storms moving through CA through the third week of January.   This year is feeling like 2000, also a weak La Nina year, when there was early season snow, then almost nothing in December (9”) due to deep Midwest/East Coast troughing, followed by an average January (68”) and the big February (124”).  Patience.  WG