Powder Forecast –Tuesday November 14th, 2017

Powder Forecast –Tuesday November 14th, 2017

Ted Schlaepfer CCM  —- Mammoth Mountain WeatherGuy

Forecast Summary:

   Light snow develops by Wednesday afternoon with snowfall increasing in intensity overnight into Thursday.  Heavy snowfall and strong winds is expected during the day Thursday tapering to moderate snowfall Thursday night under falling snow levels.  Snow showers should continue into Friday afternoon before ending with dry weather returning Saturday.  The next chance for snowfall would be overnight Sunday and next Monday followed by another chance middle/end of next week.   There could be a couple dry days before there is another chance for snowfall around the 27th.  The chances for snow may continue at times into early December or longer, but no clear signs of a major snowfall pattern.

Next update Friday 11/17

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.

http://patrol.mammothmountain.com:83/Home.aspx

**Snowfall forecast confidence ranges from very low (1) to very high (5)

Wed 11/15 = 0”
Thu 11/16 = 7 – 10” (H2O = 0.85” – 1.10”) **4
Fri 11/17 = 24 – 28” (H2O = 3.00” – 3.50”) **4
Sat 11/18 = 2 – 4” (H2O = 0.25” – 0.40”) **4
Storm Total = 33 – 42” (H2O = 4.15” – 5.00”) **4

Sun 11/19 = 0”
Mon 11/20 = 0 – 3” **2
Tue 11/21 = 3 – 6” **2
Wed – Fri 11/22 – 24 = 3 – 9”

November Snowfall = 2”
November Forecast = 30 – 50”
Detailed 5-day Snowfall Forecast:

Wed 11/15 — Light snow likely develops by the afternoon with snowfall increasing in intensity overnight and toward dawn.  Accumulations 7 – 10” by Thursday AM, around 12” up top.

Thu 11/16 — Heavy snow and strong winds expected during the day, moderate snow continues overnight and into Friday.  24 – 28” expected by Friday AM, up to 36” up top.

Fri 11/17 — Snow likely tapers off during the day, ends during the afternoon.  Accumulations 2 – 4” by Saturday AM, around 6” up top.

Sat 11/18 — No snowfall expected.

Forecast Discussion:

Short Term:

Big changes since the last update with the first strong storm now expected for Mammoth starting tomorrow and lasting into Friday.   Current satellite imagery (below) shows a deep upper level trough dropping southward from the Gulf of Alaska and about to combine with a weak subtropical low in the eastern Pacific.   Like peanut butter and chocolate, the upper low will provide the necessary cold air (blue arrow) and the subtropical low will feed it moisture (purple arrow) making a great combination to produce heavy snowfall.

   The ECM model (image below) moves the upper level low southward tomorrow and the moist southwesterly jet stream strengthens during the day for increasing upslope low level flow in the Sierra and associated orographic precipitation effects.  That means clouds will build during the daytime tomorrow and light snow could start by the afternoon with increasing snowfall intensity heading into Wednesday night.

   This time, the upper level trough will not stay to the north in the N. Sierra and it will dig southward into the central and southern Sierra by Friday (image below).  The jet stream core (purple arrow) should move southward down the Sierra during the day Thursday for heavy snow on Mammoth Mountain and other high elevation areas.  That jet will also produce very strong winds across the Sierra and Sierra crest as well Thursday, probably peaking in the early AM.  Not sure how many, if any, lifts run Thursday.

   Model QPF (Quantitative Precipitation Forecast) is generally well over 3” liquid with most models in the 4-5” range for Main Lodge for the event.  The GFS model is showing over 3” for just Thursday (image below) and the Canadian (two image below) is showing over 5” for Main and nearly 6” for the crest.   The ECM model is around 4.5” for the event.

 

  Just like last season, this storm will count as the first atmospheric river passage of the season.   We had 15 last season.   And just like last season, snow levels will be the main issue with the storm, at least for areas below Main Lodge.   Looks like snow levels will start out around 9K Wednesday afternoon with levels lowering to near 8K or into town by Thursday AM when the heaviest precipitation is about to hit.

   Snow levels will probably rise on Thursday morning into midday, possibly as high as base of Ch. 4 or even Ch. 2., before lowering overnight Thursday and into Friday down to about 5500 feet.   Overall, the bulk of the snowfall will occur with snow levels around 8200 feet with most of the precipitation falling as snow at Canyon with a period of rain possible Thursday too.  It should be all snow at Main and above for the entire event.

   Totals should be around 3 feet at Main and 4+ feet up top for the entire event.   Probably thinking that Canyon may end up with 18-24”.   It will be Sierra cement type snow (8:1 ratios), perfect first storm for laying a solid base with cold air at the end to cement it down.   Snow should continue into Friday with a few inches possible during the day Friday before snow ends during the afternoon.   Saturday will be a bluebird morning and partly cloudy day.

Long Range: 

   Models favor dry weather continuing through most of Sunday before there is a chance for snow again overnight.  The numerical guidance is generally not in agreement with the storm chance late Sunday/Monday as they disagree on the general pattern over N. America.  The GFS model (image below) digs the East Coast trough much farther south than the ECM model (two image below) with the associated Western ridge much stronger and farther west per the GFS than the ECM that has the ridge in the middle part of the country.

   That also means that the GFS model keeps the incoming short wave trough farther northward than the ECM model that moves it into central California.   Hopefully the ECM will verify and there will be more snow next Monday, because if the GFS is right, all of the cold air will stay north and it will be only subtropical moisture resulting in snow levels at 10K or higher and heavy rain at Main.

    The ensembles are totally mixed, about 50/50, some showing ridging like the GFS, and other showing an even deeper trough than the current operational ECM model.   Right now, the best forecast is some light snowfall next Monday, but it must noted that it is a low confidence forecast.

   The same issue arises with the forecast for the end of next week.   The ECM model (image below) moves a deep trough onto the West Coast and front into CA for some snowfall for Mammoth.   The GFS is showing a ridge.   The ECM ensembles are about 50/50.   Hopefully the wetter solutions will end up verifying and we will keep adding to the base.

   Long range ECM ensemble mean output is showing another trough moving into CA around November 27th for another chance for snowfall.   And the even longer range climate models like the CFS (below) are showing a wet pattern into early December.   We will have to wait and see if these solutions verify as it is still the shoulder months and the models usually don’t perform well in the longer time frames this time of year.   But we are off to a great start after the storm this week with great Thanksgiving Holiday weekend skiing/boarding looking likely.  WG

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