Powder Forecast — Tuesday January 3rd, 2017

Tuesday January 3rd, 2017

Ted Schlaepfer CCM  —- Mammoth Mountain WeatherGuy

Forecast Summary:

    A major storm cycle begins tonight and continues at times through next week.  Light snowfall turns moderate to heavy overnight and will be continuous through Wednesday and into Thursday.  Snow ends Thursday PM followed by a powder day Friday, then more a significant snow/rain storm is expected over the weekend.  Snow on Saturday likely turns to heavy rain Sunday and then back to snow next Monday.  More snow, possibly heavy, is expected again toward the middle/end of next week.  Storms, likely not at as strong, may then continue into the third week of January.

Next update Friday 1/6.

Snowfall forecast are for the Sesame snow course (Main Lodge)


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

Wed 1/4 = 16 – 18” (H20 = 1.60” – 1.85”) **4

Thu 1/5 = 32 – 36” (H20 = 3.50” – 4.00”) **4

Fri 1/6 = 2 – 3” (H20 = 0.15” – 0.25”) **3

Storm Total = 50 – 55” (H20 = 5.25” – 6.10”) **4  [5-6 feet up top]

Sat 1/7 = 0”

Sun 1/8 = 15 – 20” (H20 = 2.00” – 2.50”) **3

Mon 1/9 = 0 – 12” (H20 = 4.00” – 5.0”) **2

Tue 1/10 = 12 –15” (H20 = 1.20” – 2.00”) **3

Wed – Fri 1/11 – 13 = 12 – 36”

January Snowfall = 0”

January Forecast = 100-125”

Detailed 5-day Snowfall Forecast:

Wed 1/4 — Continuous moderate to heavy snowfall continues all day and night under windy conditions.  Accumulations 32 – 36” by Thursday  AM, 4 feet up top.

Thu 1/5 — Snow tapers off early morning and ends during the afternoon. Accumulations just a few inches more by Thursday night.

Fri 1/6 — No snowfall expected.

Sat 1/7 — Snow increases during the day and possibly becomes heavy Saturday night before changing to rain Sunday AM.  Accumulations 15 – 20” by Sunday  AM,

Forecast Discussion:

Short Term:   

  Satellite imagery (below) shows a low pressure system just off the CA coast this afternoon and about to move ashore for the beginning of a major storm cycle for CA.  This a big change from the last update as the breakthrough of the westerlies will now happen today and tomorrow instead of this weekend.

  The models move a couple low pressure systems through CA over the next 36-48 hours in the westerly flow with the upper low moving ashore Thursday (GFS below) for a long duration snow event.  The jet stream (purple arrow) will be aimed right at the central and southern Sierra and copious amounts of snowfall is expected into Thursday.

  With cold air in place from the upper low that moved into the area Sunday and Monday, snow levels will start low and then generally rise through Wednesday before falling Thursday when the upper low moves into the Sierra.  Regardless, it will be all snow on the mountain and in town with even Eagle seeing multiple feet of snow.  GFS model (image below) has more than 3” liquid for tomorrow.

  Current forecast for Main is calling for more than a foot by tomorrow AM, then about three feet falling during the day Wednesday and night, followed by just a few more inches Thursday as the storm is winding down.  The top will probably see five to six feet of snow.   Wednesday should be a tough riders of the storm day with low vis, high winds and limited chair options with Thursday looking like deep powder and lighter snowfall.  The top will probably open Friday if they can get the avy work done timely.

   High pressure briefly builds into the area Friday before a stronger storm moves into the area Saturday and through the weekend.   Snowfall will likely start during the day Saturday and increase into Saturday night as the full latitude trough approaches the coast with the GFS model moving it ashore early Monday (image below).

   The system will have significant moisture to work with as an atmospheric river is forecast to move onto the coast by Sunday morning (image below).   This AR is expected to remain in place all day Sunday before shifting southward Sunday night.

   Models are painting a very wet picture for Sunday with the GFS model (image below) showing widespread greater than 4” of liquid across the Sierra with excellent spill-over into the eastern side.   The ECM model is showing only slightly less for Sunday with the Canadian similar to the GFS model and around 6 inches.  There is a good chance for flooding on both sides of the Sierra Sunday and Monday with heavy rain falling on lots of new snow from the previous storm.

  The bigger question will be snow levels.  With that much moisture, it usually means high levels and even rain at Main. That will likely occur when the AR hits the Sierra Sunday morning (black arrows two images above) with snow levels rising to around 9K or slightly higher.  The ECM is lower with the levels and keeps them around 8.5-9K.   With 500-mb height over 570-dm, I prefer the warmer levels with heavy rain likely all day at Main and lower parts of the mountain into Monday night.  If they end up lower by only 500 feet, then snow amounts at Main will be much higher than forecast.

   The trough will dig southward Monday and snow levels will fall during the day on the back end of the storm.   And the models are suggesting enough moisture for a foot of snow or slightly more at Main by Tuesday AM.   So it looks like snow Saturday, then rain Sunday, followed by more snow Monday.  Should be all snow from McCoy upwards with another 5-6 feet possible by Tuesday, although there is a chance for a brief period of rain up to 10K or so on Sunday PM.

Long Range:

  There will probably be a brief break next Tuesday or so before the next snowfall is possible by Wednesday next week or slightly later.  The models begin to differ about timing and strength of the low pressure systems with the ECM moving the next wave into Mammoth on Wednesday.   The GFS model (image below) is slightly slower and holds it off until Thursday, although the 18Z run is similar to the ECM now.

   All the deterministic models are currently showing at least good amounts of precipitation with this next series of storms with the latest ECM showing about 5” liquid.   The Canadian and GFS are only slightly less wet.    However, the ECM ensemble mean is only showing about an inch or so, so there is still lots of uncertainty about strength and snowfall amounts as the ensemble members are showing lots of spread.

  Regardless, it looks like a stormy week ahead with the GFS model forecasting around 24” inches (2 feet) of liquid over the next ten days (image below).  That is probably overdone, but certainly 15-20 inches of precipitation could fall by the end of next week at Main.

  Longer range climate models are saying that storm chances will continue at times through the third week of January.   The ECM climate model keeps storm chances going through the rest of January, although both models are not showing a pattern as strong as the current one.  Looks like January 2017 will be a big snowfall month.  WG

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