Powder Forecast –Friday November 24th, 2017

Powder Forecast –Friday November 24th, 2017

Ted Schlaepfer CCM  —- Mammoth Mountain WeatherGuy

Forecast Summary:

   Fair and continued unseasonably warm Saturday with spring conditions on the mountain followed by colder and windy weather Sunday with snow possible by the afternoon, but more likely Sunday night.   A period of heavy snow is expected late Sunday night and Monday morning with snow tapering off Monday afternoon and ending Monday night.   The rest of the week should be dry with seasonable temperatures except for a slight chance for light snow late in the week.   A better chance for snowfall, possibly heavy, is expected over the first weekend of December with a chance it could be the start of a storm cycle lasting over the following week.

Next update Tuesday 11/28

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)

Sat 11/25 = 0”
Sun 11/26 = 0”
Mon 11/27 = 6 – 8” (H20 = 0.70” – 0.85”) **4
Tue 11/28 = 8 – 10” (H20 = 0.75” – 0.95”) **4
Storm Total = 14 – 18” **4 (H20 = 1.45” – 1.80”) **4

Wed 11/29 = 0”
Thu 11/30 = 0”
Fri 12/1 = 0 – 2”
Sat – Mon 12/2 – 4 = 12 – 30”

November Snowfall = 22”
November Forecast = 35 – 40”

Detailed 5-day Snowfall Forecast:

Sat 11/25 — No snowfall expected.

Sun 11/26 — No snowfall expected during operation hours, but there will be gusty winds.  Snowfall is expected to start Sunday evening and increase overnight.  Accumulations 6”+ by Monday AM with up to 9” up top.

Mon 11/27 —Snowfall during the day, heavy during the morning hours, tapering off afternoon, ending evening.  Accumulations 8 – 10” by Tuesday AM with 12”+ up top.

Tue 11/28 — No snowfall expected.

Forecast Discussion:

Short Term:

A strong upper level ridge remains parked over the interior West today and will hold through Saturday (image below) for continued dry weather and spring conditions on the mountain.  Temps should be in the 40s up top Saturday and middle/upper 50s to around 60 at Main.

   A change in the weather pattern back to winter starts the next day with Sunday generally the transition day as no snowfall is expected during the day.  The ECM model take the deep trough off the coast from Saturday (image above) closer to the coast and the southwest flow will increase during the day.  Expect increasing clouds, colder temperatures, and gusty winds during operations with just a chance for light snow by the afternoon.

   The models are now in general agreement that the upper level trough will take a more southerly route ashore into central California which favors better snowfall potential for Mammoth.   The latest ECM model (image below) moves a tight closed upper level 500-mb low ashore early Monday morning with the jet core (purple arrow) aimed right at the Mammoth Lake region.

   The GFS model (image below) has now trended closer to the ECM solution with the upper low taking a southerly track and the latest run of this model actually takes it even farther south than the ECM.  Under this scenario, the core of the jet stream (purple arrow) moves just south of Mammoth in the southern Sierra, although Mammoth still remains in the divergent left front quadrant of the jet resulting in good quasi-geostrophic omega lofting over the range.   That means that the front will hold together, but there is less bonus snowfall due to orographic effects (flow that is orthogonal to barrier causing air to rise/condense into precipitation).

    Model QPF (Quantitative Precipitation Forecast) ranges from about 1.25” to around 1.75” over the last few runs for the various model suites.   The latest GFS model is showing a little over 1.25” split over two days (images below) as that model is a bit faster with the eastward movement of the upper level low than the ECM model that is 3-6 hours slower.  That model is showing around 1.50” latest run and the Canadian model is similar.

   The forecast generally follows the more consistent output from the ECM model with high confidence for at least a foot at Main with probably around 15” total by Monday night when the storm ends.   I think the top will get around 20” while Canyon should pick up around a foot.   Looks like Monday will be the first riders of the storm day with the top likely closed Monday.   Tuesday will be a bluebird powder day.

Long Range:

   Looks like generally dry and seasonable weather for the rest of next week.   The numerical guidance moves a weak low ashore into NorCal early Wednesday that may result in breezy west winds (and wind buff) with a piece of energy from that low cutting off from the jet and setting up off SoCal by Thursday next week  (image below).   Looks like great skiing/riding next week under winter conditions on the mountain.

    The longer range models are now suggesting that a favorable snowfall pattern may set up over the first weekend of December.  The ECM model is the most bullish on this scenario with a deep upper level low pressure system situated right along the coast by next Sunday (image below) and Mammoth on the cold side of a strong jet stream slamming into the Sierra.   That particular upper level pattern would result in a classic Sierra snow storm with the current QPF showing enough precipitation for four feet of snow by early the following week (and two feet in Big Bear!).

   The other models are not as bullish as the ECM model, but they do show some form of deep trough along or near the coast that would result in snowfall for the Sierra and Mammoth.   It is still over a week out and the set-up will change as we get closer to the potential event, with the main message now being that there is a chance for snowfall, possibly heavy, that weekend and into the next week.   With good ensemble support and operational model agreement on a the placement of a trough along the West Coast, confidence is higher than normal for a 8-10 day forecast for at least some snowfall.

   There are also hints that there could be storms to follow over the following week.  The GFS model moves a classic high latitude type cold storm in the Sierra by Wednesday the next week (image below) followed by another one in the fantasy extended the next weekend (two images below).   These types of storms usually don’t have tons of moisture, but often produce the nicest quality cold-type powder under low snow levels.

   Overall, looks like there will be a potential storm cycle to watch for in the fantasy extended range.   Confidence is medium right now as the 12Z run of the ECM ensemble mean favors ridging after the 6th.  Good news is that the ensemble models, ECM in particular, have not performed well in that time frame yet this season, so hopefully the GFS is onto something.  WG