Powder Forecast –Friday March 6th, 2020
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 3/7 = 0 – 1”
Sun 3/8 = 2 – 3” (H2O = 0.20” – 0.30”)**3
Mon 3/9 = 0”
Tue 3/10 = 0 – 3”
Wed 3/11 = 3 – 6”
Thu 3/12 = 1 – 3”
Fri 3/13 = 0”
Sat – Mon 3/14 – 3/16 = 2 – 6”
March Snowfall = 9”
March Forecast = 40 – 60″
Detailed 4-day Snowfall Forecast:
Sat 3/7—Light snowfall develops during the late morning hours and continues at times into the evening hours before tapering off overnight. Accumulations 2 – 3” by Sunday AM, 4” up top.
Sun 3/7—No snowfall expected other than a chance for flurries late PM/evening. No accumulation expected
Mon 3/8—Light snowfall is possible during the day, better chance overnight. Light accumulations possible by Tuesday AM
Tue 3/8—Snowfall is possible at times during the day and overnight into Wednesday. Moderate accumulations (3 – 6”) possible by Wednesday AM.
Short Term (Days 1 – 4):
Infrared satellite imagery (below) today depicts an upper level trough and associated frontal systems off the West Coast and high pressure moving eastward out of CA. Clouds and winds should continue to increase rest of today as the system approaches the state.
Models (image below) split the system with the stronger portion moving into NorCal and the PacNW where most of the precipitation will occur. The tail end of a dissipating front will move into Mammoth tomorrow morning and light snowfall should start by mid or late morning and continue into the late afternoon or evening before ending overnight.
The models are not showing much snowfall with the passage of the front with the GFS (image below) in agreement with the ECM that liquid amounts will be around a quarter inch. So it should mostly be a dust on crust event, although I would not be surprised to up to 4” up top and sometimes that can be enough for fun turns.
Models then move another upper level trough southward (two images above-green box) into the eastern Pacific where it will form a closed low and cut off from the jet stream. In the meantime, weak high pressure will build into central CA Sunday and into Monday for dry weather in Mammoth except for a chance for flurries Sunday evening.
Long Range (Days 5+):
As is typical during dry winters, potential favorable patterns in the extended range end up less favorable as verification gets closer and our latest example is next week. The ECM model and others are showing a closed low off the CA coast early next week (image below), but not as deep or with the moist southwest flow the ECM model depicted in the last update.
That system will slowly move into SoCal through mid-week (image below) while weakening and bands of precipitation will move into central and southern CA starting Monday night or early Tuesday. Depending upon the exact trajectory of the upper low that is still uncertain at this time, some of those bands will produce periods of mostly light snowfall in Mammoth with snow levels around 7000 feet.
The latest GFS is the wettest of the models (image below) with over an inch of liquid in Mammoth for almost a foot of snowfall. The ECM model is drier and farther southward and only shows about a half an inch of liquid for maybe six inches of snowfall. The ECM mean has about 0.75” Monday night through Wednesday. So it looks like some decent amounts of base snow are possible, but not enough to make a huge long term difference.
Dry weather should return for the latter part of next week before the models move an upper level low southward from the Gulf of Alaska over the following weekend (image below). The ECM has trended farther eastward with the low and it is now looking like another inside slider. So many chances this season have ended up as sliders. The Canadian is the only model that still shows a favorable solution. It is still over a week out and forecasts can revert back.
The next favorable chance according to the GFS and ECM ensemble models is in the fantasy range and about two weeks out (image below). The ensembles are favoring a rather deep trough and are in strange good agreement for such a long range forecast.
There are a couple good reasons to have some faith this time. First, that is right around the spring equinox and the seasonal change should result in continued weakening of the AO strong positive phase. The stratospheric polar vortex naturally dies off during the late winter and spring and it is partly responsible for the warm/dry winter this year across most of the northern hemisphere mid-latitudes as it was unusually strong/persistent and locked into the troposphere below, keeping the cold air confined to the arctic. That could allow the jet stream to finally move southward for an extended stay.
Second, the MJO actually might be in a more favorable phase this time. As mentioned a few posts ago, I was skeptical of some of the longer term guidance showing good precipitation in early March with the MJO moving into historical dry phases 6 and 7. Now (image below) the models are forecasting it to finally move into the Indian Ocean phases two and three that historically have been associated with heavier precipitation in March, especially phase 3 in week 3. That is what the current ECM is showing. WG