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Powder Forecast –Friday January 4th, 2019

Powder Forecast –Friday January 4th, 2019

Ted Schlaepfer CCM  —- Mammoth Mountain WeatherGuy

Forecast Summary:

   Dry weather ends tomorrow late morning/midday with snowfall increasing through the evening hours before tapering in intensity overnight.  Snowfall then increases again Sunday morning and becomes moderate/heavy Sunday night before ending during the day Monday.  There will then be a break until Tuesday afternoon with snowfall likely overnight into Wednesday.  Thursday could be dry with the next chance around Friday/Saturday next week with continued chances for snowfall through the following weekend and into the next week.  Dry weather may return after mid-month. Overall, powder conditions Sunday (and storm riding), Monday, and also likely next Wednesday. Powder is also possible following weekend and at times through mid-month.

Next update Tuesday 1/8

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)

Sat 1/5 = 0”
Sun 1/6 = 12 – 15” (H20 = 1.35” – 1.60”)*3
Mon 1/7 = 15 – 20” (H20 = 1.50” – 2.00”)*3
Tue 1/8 = 1 – 2” (H20 = 0.15” – 0.25”)*3
Wed 1/9 = 8 – 12” (H20 = 0.75” – 1.25”)*2
Thu 1/10 = 1 – 2” (H20 = 0.15” – 0.25”)*3
Fri 1/11 = 0”
Sat – Mon 1/12 – 14 = 6 – 15”

January Snowfall = 0”
January Forecast = 50 –  80”

Detailed 4-day Snowfall Forecast:

Sat 1/5 —Snowfall begins late morning or midday and increases through the evening hours along with strong gusty winds.  Snowfall tapers off late at night.  Accumulations 12 – 15” Main, 18”+ up top by Sunday morning

Sun 1/6 —Snowfall increases again late morning or midday and increases through the evening hours and remains moderate/heavy overnight along with strong gusty winds.  Accumulations 15 – 18” Main, ~24” up top by Monday morning

Mon 1/6 —Snowfall tapers off during the morning hours and ends during the afternoon.  Accumulations 1 – ” Main

Tue 1/7—Snowfall develops again midday or afternoon hours and increases through overnight along with gusty winds.  Accumulations 8 – 12” Main, 12”+ up top by Wednesay morning

Forecast Discussion:

Short Term:

   The latest satellite image (below) this afternoon shows a tightly wound low-pressure system off the California coast moving eastward toward the coast tonight and eventually into Mammoth by tomorrow afternoon.  This will be the first of many storms to impact Mammoth over the next week or longer.

   The ECM model deepens the upper-level trough (image below) over the next twenty-four hours and moves into ashore Saturday and into Sunday (two images below) as a full latitude trough.   That means there will be no splitting this time when the low-pressure troughs move ashore through the upcoming weekend and the storms will move ashore full force.

   Snow should start late morning and midday tomorrow and increase in intensity through the evening hours before tapering off a bit late at night when the first front moves through the region. There will also be strong gusty winds accompanying the snowfall.  12Z ECM model has over 1.5” liquid while the GFS is only showing about 0.75”.  Forecast leans closer to the ECM based on the strength of the upper-level trough.

   A trailing storm system (green box satellite image) now just entering the central Pacific will intensify as it moves into the deep long-wave trough set-up over the West Coast.  That system will spread another round of moderate to heavy snowfall starting during the day Sunday (beware riders of the storm) and increasing in strength into the overnight hours.

   These types of systems often over-perform as the models usually under-estimate the effects of the strong warm air advection and associated upward omega forcing that produces the clouds/precipitation.  ECM model has over 2” liquid while the GFS is showing a little over an inch.  Forecast is a blend leaning toward the ECM model and another solid 15”, but I would not be surprised if it comes in heavier and up two feet at Main.

   The system will exit Monday morning (image below) and high pressure will build over the region for about 24 hours before the next trough offshore moves into CA on Tuesday night.  So, snowfall should end during the day Monday with a break in the snowfall overnight Monday and into Tuesday morning.

   Snowfall should return by Tuesday night with the timing from the ECM model saying Tuesday afternoon.  It should increase in intensity Tuesday evening and night ahead of the trough passage Wednesday morning (image below).  ECM mean has about an inch of liquid which could possibly result in close to another foot.  Current trend with the guidance is that the medium and longer range potential storms have been coming in stronger closer in time.  Hope that trend continues with this next trough.

 Long Range:  

 The longer-range guidance moves another trough toward CA by the end of next week (image below) after a dry day or two around Thursday/Friday.  The guidance seems to be favoring a southerly track with this system, similar to something typical during an El Nino year.

   Looking at the GFS spaghetti ensembles (image below) for the end of next week shows a lot of spread in timing, but most show a trough off the coast.  The operational GFS (dashed black line) and GFS control run (dashed blue line) seem to be faster than most of the ensembles in moving the under-cutting trough toward CA.  The ECM model is similar to the GFS control run with the timing.

   Not sure I buy into anything at this point as it appears to me the entire pattern for the end of next week is still evolving.   The ECM operational model moves another low pressure into CA over the weekend and then develops a closed low off the coast early the following week (image below).

     That surely could happen, but the trend with the guidance is for more energy to be moving into the southerly branch of the jet stream.  So I would not be surprised if we end up with a bigger trough when the time comes. Current forecast favors some snowfall around Friday night/Saturday next week followed more snowfall by early over the following week.   And it could be enough for powder conditions.

     So it looks like the next week or ten days will feature a few storms and amounts could add up.  ECM model is similar to the Canadian (image below) with up to 6” liquid Mammoth crest over the 10-day period.   Latest GFS was showing big amounts but has now backed off (two images below) with only a few inches liquid for Mammoth.  ECM mean has over 4” liquid next 10 days.

   Let us hope it happens as longer range climate models are saying we will shift back to a dry pattern after mid-month with both the CFS (image below) and the ECM models shifting the long-wave trough eastward for dry weather.  A lot of it will depend upon the MJO (two images below) and if it moves back into the dry phases 5-6 while also becoming a low amplitude signal.

   That could allow the ongoing stratospheric warming event to have more sway resulting in high latitude blocking and potential prolonged dry weather.  Or it could also mean El Nino will have a bigger say and there will be more under-cutting of the jet stream of those high-pressure blocks.  I’ll take the latter please.  WG