Powder Forecast –Tuesday, November 20th, 2018
Ted Schlaepfer CCM —- Mammoth Mountain WeatherGuy
Mostly sunny weather today ends tomorrow with snow expected by the afternoon. Snow will become moderate/heavy at times into early Thanksgiving before tapering off morning hours. Snow is then expected to return by Friday morning and last at times into Saturday morning before ending.
Dry weather is then expected Sunday and through early next week before the next chance for snowfall is expected around Wednesday/Thursday next week. Additional chances are then favored over the following weekend and into the next week. Overall, the storms next few days should provide the start of a needed base layer and powder days are possible by the end of next week.
Next update Tuesday 11/27
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)
Wed 11/21 = 0”
Thu 11/22 = 12 – 14” (H20 = 1.20” – 1.35”)**3
Fri 11/23 = 2 – 3” **3 (H20 = 0.20” – 0.35”)**3
Sat 11/24 = 8 – 10” (H20 = 1.00” – 1.20”)**3
Sun 11/25 = 0 – 1”
Mon 11/26 = 0”
Tue 11/27 = 0”
Wed – Fri 11/28 – 30 = 6 – 15”
November Snowfall = 0”
November Forecast = 25 – 35”
Detailed 4-day Snowfall Forecast:
Wed 11/21—Dry through midday, then snowfall develops by late afternoon and continues overnight, heavy at times. Accumulations 12 – 14” by Thanksgiving AM, 15”+ up top.
Thanksgiving 11/22—Snow showers end by lift opening, then dry until late at night when snow likely redevelops. Accumulations 2 – 3” b Friday AM.
Fri 11/23—Snow is expected at times during the day and overnight. Snow levels rising by the late afternoon/evening to near 8K. Accumulations 8 – 10” by Saturday AM.
Sat 11/24—Snow showers end morning hours, then dry rest of the day. Maybe an inch accumulation.
Mostly sunny weather ends today with increasing clouds expected during the day tomorrow. Pacific satellite imagery shows a developing low-pressure system and a cold front off the California coast (image below) that will move ashore onto the coast early Wednesday. That will lead to snowfall starting in Mammoth late afternoon tomorrow and then lasting overnight into Thanksgiving morning.
The latest ECM model (image below) moves the trough axis through the Sierra 4 AM Thursday and snowfall should taper off fairly quickly afterward. Latest QPF (Quantitative Precipitation Forecast) from the ECM is around 1.35” and the GFS is slightly lower. Snow levels won’t be an issue, starting out around 6.5K before lowering to around 5K early Thursday. Looks like around a foot for Main Lodge and 15+ for the powder fields.
There will be a break between storms with dry weather expected most of Thanksgiving and into the evening hours before the next system possibly arrives late at night. The models (ECM below) move the upper-level low mostly eastward well north of Mammoth, but the system will have abundant moisture (weak Atmospheric River or AR) and a strong associated southern branch of the jet stream.
That means the Sierra from about Kirkwood northward will receive the bulk of the precipitation and Mammoth will be in the southern fringe. The ECM model is the most aggressive with the southern extent of the precipitation with the GFS farther northward and shows less than an inch for Mammoth (image below). The Canadian is more similar to the ECM and shows about 1.25”. The ECM means has a little over an inch and current forecast favors a blend of the models.
The other factor to consider with the second storm is snow levels. They should start out well below town Friday morning with the cold air already in place, but the warm advection associated with the AR should producing rising levels through the afternoon and evening possibly up to 8K. It should stay all snow at Main, but the quality of the snow should get heavier by Saturday AM when it finally ends. Overall, the second storm should produce just under a foot at Main of good base type snowfall with lower snow to water ratios than the first storm.
Dry weather should return by Saturday midday and then last for the rest of the Holiday weekend. ECM model keeps the dry weather ongoing with a ridge (image below) through early next week.
Longer range guidance is then favoring the passage of another trough around the middle/end of next week. The ECM operational model (image below) moves a fast moving upper level low through the Sierra next Wednesday night/Thursday with about a foot of snowfall for Mammoth followed by ridging. The Canadian is similar.
However, the GFS is faster and not nearly as progressive with the longwave trough. It moves a low into NorCal a day early (image below) and around next Wednesday while keeping the jet stream flow off the coast zonal end of next week. That allows subsequent short waves to move into the state (two images below) for additional rounds of precipitation and snowfall for Mammoth into the following weekend (three images below). GFS adds up the snowfall over the 10 day period to over 3 feet (four images below).
A few of the ECM ensembles show the GFS solution, but the vast majority are more progressive like the operational model. However, many of the ensembles show the passage of another upper-level trough over that same first weekend of December. So the exact solutions are still mixed, but there certainly looks like a decent chance for two more storms end of next week and again over the following weekend. And hopefully, with an established small base, these could be powder day storms.
For what it is worth, the fantasy period of the GFS keeps the storm train rolling into the middle part of the following week. Not sure I believe that as more ensembles favor ridging, but the 15-day model QPF (image below) would be great if it materializes with almost 5-6” liquid for Mammoth. Nonetheless, the longer range ECM climate model shows more storm chances over the second week of December and through mid-month. So hopefully there will be additional powder days on a building base layer. WG