Powder Forecast –Tuesday March 20th, 2018

Ted Schlaepfer CCM  —- Mammoth Mountain WeatherGuy

Forecast Summary:

     Snow continues Wednesday and becomes heavier by the afternoon/evening and also when snow probably changes to rain at Canyon.  Heavy wet snowfall continues overnight Wednesday along with strong winds with the heaviest period of precipitation expected Thursday morning when the snow may change to rain at Main too and likely up to Ch. 2.  Snow levels fall Thursday PM/night when heavy snow/rain changes to moderate snow, ending early Friday AM.  Friday should be dry and early Saturday too, then more moderate snow is possible Saturday night and into Sunday morning.  Dry weather is then expected Monday and rest of month with the next chance in early April.  Overall, powder days are expected tomorrow into Friday and then again Sunday, although powder conditions should only be expected in the upper elevations Thursday as any new snow near Canyon will be rain affected.

Next update Friday 3/23

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 3/21 = 8 – 10” (H20 = 0.75” – 1.00”) **4
Thu 3/22 = 12 – 16” (H20 = 2.25” – 2.50”) **3
Fri 3/23 = 14 – 18” (H20 = 2.75” – 3.00”) **3
Storm Total = 34 – 44” (H20 = 5.75” – 6.50”) **3

Sat 3/24 = 0”
Sun 3/25 = 6 – 9”
Mon 3/26 = 0”
Tue 3/27 = 0”
Wed – Fri 3/28– 30 = 0”

March Snowfall = ~92”
March Forecast = 120 – 135”

Detailed 5-day Snowfall Forecast:

Wed 3/21 —Moderate/heavy snowfall during the day becomes very heavy wet snow overnight or possibly heavy rain by early Thursday.   Accumulations 12 – 16” by Thursday AM with up to 24” up top.

Thu 3/22—Heavy wet snow/rain in the morning turns to moderate snow PM and overnight.  Accumulations 14 – 18” by Friday AM with 24″+ up top.

Fri 3/23— No snowfall expected after a chance early AM.  No accumulation after dawn.

Sat 3/24—Chance for snow by late afternoon with snow likely overnight.   Accumulations 6 – 9” by Sunday AM and up to a foot up top.

Forecast Discussion:

Short Term:

  Satellite imagery (below) shows clouds having moved into CA associated with a warm front that is part of a larger upper level trough off the CA coast extending southwest toward Hawaii.  Light to moderate snowfall has begun in Mammoth as a result and should continue overnight while increasing intensity a bit.

   The satellite image also shows a plume of moisture stretching back into the subtropical Pacific ahead of a slow moving cold front that will progress toward the coast tomorrow.  Embedded within that subtropical plume is an atmospheric river (image below) which is a concentrated area of water vapor in the lower troposphere.  You should remember them from last season when about 15 ARs moved into CA and Mammoth over the course of that huge 2016-17 season.

   The models move the upper level trough onto the coast early Thursday (image below) and that is when the most intense precipitation consisting of heavy rain/snow and strong winds is expected with this storm system.   ECM model has over 1.5” liquid between 5 AM and 11 AM Thursday.

    ARs are typically quite mild and there were many rain events last season at 8-8.5K and heavy snow at 10K associated with their landfall and this system will be no different.   Expect the snow to change to rain at Canyon as early as Wednesday late AM/afternoon and it will be likely by overnight into Thursday.  Snow levels early Thursday peak of the event will probably rise to near Ch 2  before colder air spills into Mammoth during the afternoon and night when the precipitation intensity decreases back to moderate.

   The ECM and wettest models are showing around 7-8” of liquid for the crest and around 7” for Main while the drier GFS has about 5-6” for Main and has most of it falling Thursday (image below).  Forecast is a blend of the models are favors around 6” plus for Main and 7” liquid up top.  Snow ratios will be under 8”:1” by tomorrow and could get quite low during the peak event and could be as low as 5”:1” of super wet and heavy Sierra cement.    While there could be a drier layer of snow as the event is ending, this storm will not be like the last few storms of cold dry powder.

   Snow ends early Friday and Friday should be a dry day other than a chance for a light snow shower during the morning.   Climax should be filled in again now after the avy a few weeks ago with probably 5 feet of snow up top in the powder fields.  Let’s hope there aren’t any big slides with avy control as this base snow will likely extend the season into June, if not 4th of July says the Snowman.

   The dry weather lasts into Saturday before the models move the main upper level low pressure system into CA Saturday (image below) into Sunday for another round of snowfall.  Timing right now has most of the snow falling overnight Saturday and into Sunday morning.

   This time the system won’t have a lot of moisture to work with, but will be colder with snow levels around 4000 feet and the drier quality snow too.  GFS is only showing around half an inch (image below) while the ECM has closer to an inch.  Forecast favors 6-9” right now and probably a foot up top and should be a fun layer on top of the cement from the previous storm.

Long Range:

   Long range guidance is then favoring a large scale pattern change  next week with high pressure mostly replacing the trough along the West Coast and CA for a return to dry weather.   The 12Z run of the ECM has the ridge edging into CA by the middle part of next week (image below) shutting closed the storm door that produce the big March.

   Cold dry northerly flow should continue Monday/Tuesday followed by fair and warmer weather, but nothing too warm, toward the end of next week when the ridge moves farther eastward over CA.  Longer range GFS ensemble mean favors this pattern through the following weekend (image below) and end of the month.

   The fantasy range GFS ensemble then redevelops the trough along the West Coast and ridge in the Aleutians and Greenland again (image below).   The 12Z ECM mean is showing it as well.  So there is a chance that snowfall could return over the first full week of April.

   The CFS model favors at least some storms over the first part of the month (image below), although it isn’t showing anything big right now with a normal/slightly below average forecast.   However, looking back at old forecasts from earlier this month, the CFS didn’t catch the current pattern well in the extended either as the storms came in much bigger.  Hopefully that will happen again for spring powder days.  WG