Powder Forecast –Tuesday May 22nd, 2018

Ted Schlaepfer CCM  —- Mammoth Mountain WeatherGuy

Forecast Summary:

  Partly cloudy next few days with a chance each for afternoon showers and thunderstorms, but not as widespread as last few days.  A chance for light snow is then possible by Friday night and into early Saturday with a continued chance for light snow showers Saturday.  Partly cloudy Sunday with a chance for PM rain showers, then mostly fair Memorial Day and through the middle part of next week and warmer with just a slight chance for a late PM shower.  Cooler weather is possible end of next week followed by mostly seasonable weather through early June with late afternoon shower/thunderstorms.  Overall, significant snowfall resulting in powder conditions is not expected moving forward.

Last update for the season, next update November 2018

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.

Sesame Snow Course

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

Wed 5/23 = 0”
Thu 5/24 = 0”
Fri 5/25 = 0”
Sat 5/26 = 1 – 3”
Sun 5/27 = 0 – 1”
Mon 5/28 = 0”
Tue 5/29 = 0”
Wed – Fri 5/30 – 6/1 = 0”

May Snowfall = ~4”
May Forecast = 5 – 8”

Detailed 5-day Snowfall Forecast:

Wed 5/23 and Thu 5/24 — No snowfall expected both days, although afternoon/evening rain showers or thunderstorms are possible each day.

Fri 5/25 and Sat 5/26 — Chance for light rain/snow showers by Friday afternoon with light snowfall possible overnight and into early Saturday.  Snow showers then possible at times Saturday.  Accumulations 1 – 3” at Main with up to 6” up top.

Forecast Discussion:

Short Term:

   The upper level low pressure system that has been nearly stationary in Nevada and has produced lots of showers and fog on the mountain (and kept the top closed) last few days will weaken and drift a bit farther northern Wednesday (image below).   That means there should be less clouds and showers tomorrow with only isolated showers Thursday as that low exits farther eastward.   Temps should also warm up a bit and generally be seasonable and spring-like.

  Another cut-off low pressure system will then move onto the coast early Friday (image below) before moving eastward into central/southern CA early Saturday (two images below).   That system will probably be deep enough for some organized precipitation (as opposed to the hit and miss showers last few days) to move into the Sierra Friday afternoon and/or early Saturday.

   The GFS model is slightly deeper than the ECM model and develops some fairly decent precipitation for May (image below) in the wraparound flow early Saturday when the low drifts toward the southern Sierra.   It has snow levels down to town level overnight Friday and early Saturday as well.  The latest ECM model is not as bullish and has snow levels around 8-8.5K early Saturday.

   The GFS would result in a solid few inches at Main while the ECM is maybe an inch or two.    These cut-off lows are tricky to forecast even out in time just a few days, especially when the system is already on the cusp of being too weak to produce snowfall.   Current forecast follows the 12Z ECM ensemble mean that is closer to the GFS and shows almost a third of an inch.   With low ratios this time of year, probably only a couple inches, but maybe there could be pockets of up to 6” up top.  There will probably be some fun turns Saturday morning, but likely not deep powder.

Long Range:  

   The upper low exits slowly eastward Sunday and there could be continued wrap-around showers, but snow levels will likely be 10K or higher by the afternoon.   Not expecting more than a trace to an inch up top.

   High pressure will then build into the area (image below) through early next week for mostly fair and warmer weather.  There should be less afternoon shower and thunderstorm activity than of recent with mostly clear skies during prime shredding hours in the mid to late morning hours, but there is still a chance, primarily after operational closing time (2:30 PM).

   That weather should last until the end of next week when a trough of low pressure moving into the PacNW (image below) provides some cooling along with drier southwest flow that may blow the thunderstorm moisture eastward.


   Longer range GFS ensembles then favor a weak trough along the coast and high pressure across the interior over the first few days of June (image below).  That could mean another cut-off low pressure system near or over CA that could result in increased PM shower/thunderstorm activity, but likely no snowfall as there is rarely enough cold air in June for frozen precipitation other than thunderstorm hail.

  Super long range GFS ensemble then move a longwave trough into the PacNW heading into the second week of June (image below) that would mean seasonable weather and less afternoon shower/thunderstorm activity again.    Temps through mid-June may be near normal or slightly above normal at times for generally a normal melt rate on the mountain as there are no clear signs of any major heat waves into mid-June.  Have a great rest of season and summer. WG