Powder Forecast — Friday January 6th, 2017

Friday January 6th, 2017

Ted Schlaepfer CCM  —- Mammoth Mountain WeatherGuy

Forecast Summary:

    Part two of the major storm cycle begins Saturday, peaks Sunday and into Monday with a mix of very heavy rain and snow, with part three expected Tuesday night and Wednesday as another round of heavy snowfall with a fourth storm possible Wednesday night and Thursday.  Storms, likely not at as strong, could move into Mammoth over the following MLK Holiday weekend before dry weather likely returns over the following week.   There could be weak storm at times for the rest of the month with the next chance for stronger storm toward the end of January.

Next update Tuesday 1/10.

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

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

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

Sat 1/7 = 1 – 2” (H20 = 0.15” – 0.25”) **4

Sun 1/8 = 16 – 20” (H20 = 2.90” – 3.25”) **4

Mon 1/9 = 12 – 20” (H20 = 4.00” – 4.50”) **3

Tue 1/10 = 12 –15” (H20 = 1.50” – 2.00”) **4

Storm Total = 41 – 57” (H20 = 8.55” – 10.00”) **4

Wed 1/11 = 20 – 23” (H20 = 2.00” – 2.25”) **3

Thu 1/12 = 11 – 14” (H20 = 1.00” – 1.25”) **3

Storm Total = 31 – 37” (H20 = 3.00” – 3.50”) **3

Fri – Mon 1/13 – 15 = 12 – 20”

January Snowfall = 42.5”

January Forecast = 135 -165”

Detailed 5-day Snowfall Forecast:

Sat 1/7 — Snow increases during the day and possibly becomes heavy Saturday night before changing to rain by Sunday AM.  Accumulations 16 – 20” by Sunday AM.

Sun 1/8 — Heavy rain mixed with snow at times expected during the day and into Sunday evening, heaviest rain expected in the AM.   Rain changes back to heavy snow Sunday night and into Monday.   Accumulations 12 – 20” by Monday AM; 5 – 6 feet up top including Saturday.

Mon 1/9 — Snow continues during the day and tapers off Monday night.  Accumulations 12 – 15” by Tuesday AM.

Tue 1/10 — Snowfall increases again during the afternoon and becomes heavy overnight into Wednesday.  Accumulations 20 – 23” by Wednesday AM.

Forecast Discussion:

Short Term:   

  Satellite imagery (below) shows weak high pressure has built into CA in the wake of storm number one that produce over 40” of snow at Main and up to 84” up top.   That high will move eastward tonight as a deep and cold upper level low pressure system located in the Gulf of Alaska moves southward around the blocking high in the Aleutians and combines with a subtropical low pressure system in the eastern Pacific that is slowly moving toward the coast.

   Explosive cyclogenesis is expected Saturday off the coast when the systems combine to form a full latitude trough and extensive subtropical moisture will be entrained into the storm system and will move ashore as an atmospheric river (AR) over the weekend.  The GFS model moves the bulk of the AR to the coast Sunday (image below) with the subtropical moisture increasing during the day Saturday.

   The models are saying the full latitude trough will move onto the coast Sunday afternoon (image below) and the cold front will slide southward Sunday night and early Monday with continued moist upslope flow Monday over the Sierra.

   The precipitation will likely start early Saturday and increase during the day with the heaviest precipitation forecast for Sunday, particularly during the morning and again at night, with precipitation continuing Monday before finally tapering off Monday night. Model QPF is impressive for each day (images below) with Sunday particularly impressive under the effects of the AR when 5-7 inches may fall in 24 hours.  Overall, Main lodge will probably see 9-10” of liquid precipitation with probably around foot or slightly more up top.  Still looks like flooding is possible on both sides of the Sierra.

   The big question with this event remains the snow levels.   Particularly, how fast do they rise Saturday/Saturday night and then fall Sunday night and into Monday.  Not much has changed since the last update except that models now lower snow levels faster Sunday night when the cold front sags southward as the upper trough digs southward.

  Looks like evaporative cooling will keep snow levels around 8-8.5 K Saturday and into Saturday evening before the AR moves into the area overnight in the form of a strong warm front with the snow changing to rain at Main as snow levels rise to close to 9.5 K during the morning hours. Snow levels will probably then undulate between 8.8 and 9.2 K during the day/evening before lowering back to 8K Sunday night and then 5.5K during the day Monday.

   That means there will be accumulating snow during the day Saturday (riders of the storm opportunity- best bet ch 22 if open) and into Saturday night, but then no real accumulation during the day Sunday (not a good riders day), with snow then accumulating again overnight Sunday and through Monday.   The snow may start out light, but it will end heavy and classic Sierra cement with maybe a small layer of drier snow Monday at the end of the storm.   Total accumulations from the storm could approach 3-4 feet at Main with up to 7 feet up top.

    There will be a small break Tuesday morning before the next storm moves into Mammoth Tuesday night and Wednesday.   Models are saying the deep upper low associated with the weekend storm will remain off the coast and then combine with another short wave before moving ashore Tuesday night and Wednesday (image below).

   This will also be big storm system with a strong westerly jet impacting the Sierra.  It won’t have as much moisture to work with, but it will be colder, with snow levels around 6000 feet and all snow for the mountain and town.  Model QPF for the storm is in the 3-4” range which would be another 3 feet at Main and 4 plus up top.  Details will be sorted out on Tuesday, but there could be powder days every day next week.

Long Range:

  There will probably be one last strong storm late Wednesday and next Thursday as the westerly flow continues off the Pacific.   The GFS model (image below) moves the short wave ashore early Thursday with snow increasing during the day.   The latest ECM model is weaker and splits the low off the coast, but last night’s run showed a whopper again with another 3 feet at Main.

   The GFES spaghetti ensembles (image below) show that most of the ensembles favor a lower latitude westerly jet flow into CA, but there are few outliers that are farther North.  The ECM mean shows about 1-2″, which is probably the best forecast right now.

   There could be another storm late over the weekend as the GFS model (image below) splits a short wave from the flow into CA late Sunday and into the MLK holiday.  However, the ensembles (two image below) only show a few members supporting a trough and most actually favor ridging and dry weather which will probably be welcome after all the snow and weather over the previous week.

   That is also what the climate models are now showing with a period of dry weather starting around or just after the holiday weekend and continuing for most of the next week.   Longer range models are saying that it will be mostly dry until the end of the month when there is a chance for storminess to return.  WG

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