Friday December 9th, 2016
Ted Schlaepfer CCM —- Mammoth Mountain WeatherGuy
Rain or snow starts early Saturday and increases Saturday night before ending early Sunday. Rest of Sunday will be dry with the dry weather continuing into Monday. There is a chance for rain/snow on Monday night with a good chance for more precipitation by the middle part of next week followed by a chance for significant snow by the end of the week and/or following weekend. Longer range guidance suggests a chance for snow at times through the end of the month.
Next update Tuesday 12/13.
Snowfall forecast are for the Sesame snow course (Main Lodge)
**Snowfall forecast confidence ranges from very low (1) to very high (5)
Sat 12/10 = 0”
Sun 12/11 = 6 – 10” (H2O = 1.75” – 2.50”) ** 4
Mon 12/12 = 0”
Tue 12/13 = 0” – 3” (H2O = 0.10” – 0.50”) ** 2
Wed 12/14 = 0” – 12” (H2O = 0.00” – 1.50”) ** 2
Thu 12/15 = 0” – 6”
Fri 12/16 = 0” – 12”
Sat – Mon 12/17 – 19 = 12 – 36”
December Snowfall = 9”
December Forecast = 50 – 70”
Detailed 5-day Snowfall Forecast:
Sat 12/10 — Snow/rain increases during the morning with snow levels 8500-9000 during the day falling to 8000-8500 overnight. Accumulations are expected to be a mushy 6 – 10” by Sunday AM. Maybe a couple inches at Canyon early Sunday, probably mostly rain. Up to 2 feet possible up top, more than a foot at McCoy.
Sun 12/11 — Precipitation likely ends before the lifts open, dry rest of the day.
Mon 12/12 — There is a chance for rain/snow overnight Monday and into Tuesday. Any accumulations light and under 3”.
Temps have become rather mild in the subtropical flow that continues into CA today. That doesn’t lend itself well for a big snowfall event associated with the incoming low pressure system models are forecasting to move into NorCal early tomorrow and eastward during the day (image below).
That is because the low pressure system has an atmospheric river embedded within it and that feature will also move inland during the day Saturday (image below). The source for the AR is near Hawaii and in general AR’s are a tropical or subtropical phenomenon and not prolific snowmakers except at the highest elevations of the Sierra.
It will move through the Sierra rather quickly in about 24 hours, but precipitation totals will likely still be impressive as the orographic upslope flow enhances the rainfall significantly under this scenario. Models, GFS in particular (image below), is showing greater than 4” of liquid across much of the central Sierra, generally from the crest westward.
Models taper off the precip southward toward the southern Sierra with the bulk of the rain and high elevation snow staying north of Mammoth. The GFS now moves the front slightly farther southward than the ECM model with the main difference being slightly lower snow levels for the back end of the storm per the GFS.
Nonetheless, snow levels will likely start around 9000 feet or so and range between 8500-9000 feet during most of the event with a chance they could be as high as 9500 feet. All models do lower the levels overnight Saturday during the back end of the storm with the GFS all the way down to near 7000 feet early Sunday, probably too low. With the subtropical nature of the air mass and minimal cold air, current forecast favors snow levels staying near or above 8000 feet into early Sunday.
Overall, that means rain for the lower part of the mountain including Canyon for the majority of the event. Maybe Canyon could see a few inches at the tail end of the storm early Sunday. At Main, there might not be much accumulation until Saturday night with a mix of rain/snow during the day with current forecast favoring 5-10” by Sunday AM of generally mushy snow, depending upon how fast snow levels fall Saturday night. It should be all snow from McCoy upward with up to 2 feet of base type snow possible up top by Sunday when the storm ends.
Dry weather returns during the day Sunday and should continue through most of Monday. That is when models diverge on what happens next. However, both the GFS and ECM bring a warm front back northward through the Sierra overnight Monday and into Tuesday for a chance for precipitation. Unfortunately, snow levels may be 9000 feet or higher per the ECM with the GFS much lower and around 7000 feet. No significant precipitation is expected until possibly Tuesday anyway.
All the latest guidance from the models is showing significant precipitation next week. All the models are showing it occurring on different days. The GFS model (image below) moves into central CA a robust short wave around Tuesday next week for a round of snow in Mammoth greater than a foot (QPF ~ 2” liquid). The ECM keeps it off the coast for a day or two with the moist front and precipitation aligned much farther north before swinging it southward Thursday next week.
The GFS on the other hand, brings a different short wave southward and develops it into a deep closed low off the CA coast around next Friday (image below) before swinging it inland over the weekend for a major storm and snowfall event.
Completely different, the ECM instead moves another deep upper low southward from the Gulf of Alaska around Friday/Saturday next week, re-enforcing the longwave trough along the coast, and bringing in a round of cold, dry, hero powder. Both models show significant snowfall next week with the GFS model snowfall forecast off the scale (image below).
Looking at the GFES spaghetti ensembles (image below) shows a wide range of possible solutions for next week with a few ensemble supporting the GFS operational model (dashed black line), others showing the ECM solution, and the control run (blue dashed line) something completely different and dry.
Overall, the models will continue to flip and flop with different solutions until we get closer in time, so I don’t want to try to figure out the details now. The current forecast favors some snowfall by the middle part of next week with a good chance for more significant snowfall by the end of next week and into the following weekend. Confidence is low in the details and timing, but rather high that there will be a good or even great storm by the end of next week.
There will probably be a dry period to follow any storm event next week. Then then climate models are showing a chance for storms at times through the end of the month and into January with the CFS model (image below) a bit more bullish than the ECM weekly climate model that did another 180 flip back to less dry from the previous run. Still don’t have a lot of faith right now in those models, but a chance for storms at times seems reasonable, hoping with a nice base by then to go with it. WG