Powder Forecast — Friday December 9th, 2016

Friday December 9th, 2016

Ted Schlaepfer CCM  —- Mammoth Mountain WeatherGuy

Forecast Summary:

    Rain or snow starts early Saturday and increases Saturday night before ending early Sunday.  Rest of Sunday will be dry with the dry weather continuing into Monday.  There is a chance for rain/snow on Monday night with a good chance for more precipitation by the middle part of next week followed by a chance for significant snow by the end of the week and/or following weekend.  Longer range guidance suggests a chance for snow at times through the end of the month.

Next update Tuesday 12/13.

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 12/10 = 0”

Sun 12/11 = 6 – 10” (H2O = 1.75” – 2.50”) ** 4

Mon 12/12 = 0”

Tue 12/13 = 0” – 3” (H2O = 0.10” – 0.50”) ** 2

Wed 12/14 = 0” – 12” (H2O = 0.00” – 1.50”) ** 2

Thu 12/15 = 0” – 6”

Fri 12/16 = 0” – 12”

Sat – Mon 12/17 – 19 = 12 – 36”

December Snowfall = 9”
December Forecast = 50 – 70”

Detailed 5-day Snowfall Forecast:

Sat 12/10 — Snow/rain increases during the morning with snow levels 8500-9000 during the day falling to 8000-8500 overnight.  Accumulations are expected to be a mushy 6 – 10” by Sunday AM.   Maybe a couple inches at Canyon early Sunday, probably mostly rain.   Up to 2 feet possible up top, more than a foot at McCoy.

Sun 12/11 — Precipitation likely ends before the lifts open, dry rest of the day.

Mon 12/12 — There is a chance for rain/snow overnight Monday and into Tuesday.  Any accumulations light and under 3”.

Forecast Discussion:

Short Term:   

   Temps have become rather mild in the subtropical flow that continues into CA today.   That doesn’t lend itself well for a big snowfall event associated with the incoming low pressure system models are forecasting to move into NorCal early tomorrow and eastward during the day (image below).

gfs_namer_036_

   That is because the low pressure system has an atmospheric river embedded within it and that feature will also move inland during the day Saturday (image below).  The source for the AR is near Hawaii and in general AR’s are a tropical or subtropical phenomenon and not prolific snowmakers except at the highest elevations of the Sierra.

ivt_uswc_latest_f030

   It will move through the Sierra rather quickly in about 24 hours, but precipitation totals will likely still be impressive as the orographic upslope flow enhances the rainfall significantly under this scenario.   Models, GFS in particular (image below), is showing greater than 4” of liquid across much of the central Sierra, generally from the crest westward.

gfs_24hr-day2

    Models taper off the precip southward toward the southern Sierra with the bulk of the rain and high elevation snow staying north of Mammoth.   The GFS now moves the front slightly farther southward than the ECM model with the main difference being slightly lower snow levels for the back end of the storm per the GFS.

   Nonetheless, snow levels will likely start around 9000 feet or so and range between 8500-9000 feet during most of the event with a chance they could be as high as 9500 feet.   All models do lower the levels overnight Saturday during the back end of the storm with the GFS all the way down to near 7000 feet early Sunday, probably too low.   With the subtropical nature of the air mass and minimal cold air, current forecast favors snow levels staying near or above 8000 feet into early Sunday.

    Overall, that means rain for the lower part of the mountain including Canyon for the majority of the event.   Maybe Canyon could see a few inches at the tail end of the storm early Sunday.  At Main, there might not be much accumulation until Saturday night with a mix of rain/snow during the day with current forecast favoring 5-10” by Sunday AM of generally mushy snow, depending upon how fast snow levels fall Saturday night.  It should be all snow from McCoy upward with up to 2 feet of base type snow possible up top by Sunday when the storm ends.

    Dry weather returns during the day Sunday and should continue through most of Monday.   That is when models diverge on what happens next.   However, both the GFS and ECM bring a warm front back northward through the Sierra overnight Monday and into Tuesday for a chance for precipitation.   Unfortunately, snow levels may be 9000 feet or higher per the ECM with the GFS much lower and around 7000 feet.  No significant precipitation is expected until possibly Tuesday anyway.

Long Range:

  All the latest guidance from the models is showing significant precipitation next week.   All the models are showing it occurring on different days.   The GFS model (image below) moves into central CA a robust short wave around Tuesday next week for a round of snow in Mammoth greater than a foot (QPF ~ 2” liquid).   The ECM keeps it off the coast for a day or two with the moist front and precipitation aligned much farther north before swinging it southward Thursday next week.

gfs_namer_108_

   The GFS on the other hand, brings a different short wave southward and develops it into a deep closed low off the CA coast around next Friday (image below) before swinging it inland over the weekend for a major storm and snowfall event.

gfs_namer_180_

    Completely different, the ECM instead moves another deep upper low southward from the Gulf of Alaska around Friday/Saturday next week, re-enforcing the longwave trough along the coast, and bringing in a round of cold, dry, hero powder.  Both models show significant snowfall next week with the GFS model snowfall forecast off the scale (image below).

gfssw_snow_240

   Looking at the GFES spaghetti ensembles (image below) shows a wide range of possible solutions for next week with a few ensemble supporting the GFS operational model (dashed black line), others showing the ECM solution, and the control run (blue dashed line) something completely different and dry.

gfs_2016120912_spag_180

   Overall, the models will continue to flip and flop with different solutions until we get closer in time, so I don’t want to try to figure out the details now.   The current forecast favors some snowfall by the middle part of next week with a good chance for more significant snowfall by the end of next week and into the following weekend.   Confidence is low in the details and timing, but rather high that there will be a good or even great storm by the end of next week.

  There will probably be a dry period to follow any storm event next week.   Then then climate models are showing a chance for storms at times through the end of the month and into January with the CFS model (image below) a bit more bullish than the ECM weekly climate model that did another 180 flip back to less dry from the previous run.  Still don’t have a lot of faith right now in those models, but a chance for storms at times seems reasonable, hoping with a nice base by then to go with it.  WG

wk3-wk4_latest-naprec

Posted in Mammoth Lakes Weather Forecast, Mammoth Mountain Weather Discussion, Mammoth Weather | Tagged | Comments Off on Powder Forecast — Friday December 9th, 2016

Powder Forecast — Tuesday December 6th, 2016

Tuesday December 6th, 2016

Ted Schlaepfer CCM  —- Mammoth Mountain WeatherGuy

Forecast Summary:

    Dry weather continues during the day tomorrow with increasing clouds with snow developing Wednesday night and continuing through Thursday.  Another round of snowfall develops Friday and probably continues through most of Saturday when it could be heavier.   Sunday may be dry, then there is a chance for light snowfall early next week followed by a chance for heavier snowfall toward the middle/end of next week.  Longer range models show a chance for storms at times for the last part of December, although confidence is low.

Next update Friday 12/9.

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)

Wed 12/7 = 0”

Thu 12/8 = 2 – 3” H2O = 0.15” – 0.25”) **4

Fri 12/9 = 7 – 9” (H2O = 0.75” – 1.00”) ** 3

Sat 12/10 = 5 – 7” (H2O = 0.85” – 1.10”) ** 3

Sun 12/11 = 8 – 12” (H2O = 0.95” – 1.50”) ** 3

Mon 12/12 = 0”
Tue 12/13 = 0”

Wed – Fri 12/14 – 16 = 3 – 12”

December Snowfall = 5”

December Forecast = 45 – 60”

Detailed 5-day Snowfall Forecast:

Wed 12/7 — Dry during the day with snowfall developing Wednesday night.  Accumulations are expected to be light < 3” by Thursday AM

Thu 12/8 — Light to moderate snowfall is expected during the day and through Thursday night, tapering off toward dawn.  Accumulations 7 – 10” by Friday AM when lifts open.

Fri 12/9 — Snowfall develops again during the day and through Friday night.  Accumulations 6 – 9” by Saturday AM when lifts open.

Sat 12/10 — Snowfall, possibly heavy at times during the morning, continues through the day before ending Saturday night.  Accumulations 8 – 12” by Sunday AM when lifts open.

Forecast Discussion:

Short Term:   

  A cold front is currently moving through CA today with just an increase in winds and slightly colder temperatures.   Satellite imagery (image below) shows the front is part of a wave train family in the eastern Pacific that has a moisture plume extending back to Hawaii (same plume that produced heavy snow on the top of volcanoes on the Big Island).    That plume will begin to move toward the coast tomorrow for increasing cloudiness.

latest_west

  My hunch about the MJO appeared to be right on as the models have switched from dry to wet since the last update when they didn’t have a handle on the feature.  Now the models are in agreement that it will move into the wet phase 3 (image below) and increase the strength of the southern branch of the jet stream into CA later this week.

ncpe_phase_21m_small

   There is an atmospheric river embedded within the moisture plume, but it isn’t particular strong overall as the wind component (integrated water vapor flux has two terms, moisture and wind speed) is rather weak as the jet stream isn’t particularly robust off the coast right now.

  Nonetheless, the AR will move onshore Thursday and snowfall will increase during the day as the first low pressure system moves inland within the moist subtropical flow.   Snow levels will rise during the day Thursday, but it should still be all snow on the mountain (snow levels ~7K).   The GFS (image below) is wetter than the ECM and shows almost an inch of QPF, although it keeps most of the precipitation on the west side of the Sierra as the weak jet will limit spill-over.

gfs_24hr-day3

   A second low pressure system is then expected to move into CA on Friday.   Models differ on the timing and strength of the storm with the GFS generally faster and drier.   The ECM model, which I generally prefer within a few days of the storm, pushes a stronger jet stream ashore which produces more orographic precipitation over the Sierra including better spill-over.

   The ECM mean is fairly bullish on at least an inch of precipitation while the deterministic run from 12Z today shows about 2.5” liquid.  The GFS weakens the feature instead of strengthening and has less than an inch with the precip ending Friday night while the ECM has heavy snow Saturday morning and into the afternoon.    The Canadian model is faster like the GFS and keeps the heavier precipitation to the north.

   Overall, the forecast leans toward the ECM mean right now with plenty of uncertainty.   Snow levels will rise a bit more Friday and could get near 8500 feet by Friday afternoon.   So it will be a sloppy snow at Main and probably rain at Eagle and maybe Canyon too. Snow levels do fall according to the ECM on Saturday during the day.  Regardless, it will be all snow up top and there will probably be around 3-4 feet when the precipitation finally ends Saturday night.  Hoping for about 2 feet at Main for the whole event and it will be base type snow, not hero powder.

Long Range:

 There will probably be a break Sunday and into Monday after the trough moves eastward and high pressure builds back into the central and southern part of the state.  The numerical guidance, however, is showing the moist subtropical plume will remain intact off the coast and move ashore into NorCal as a strong warm front.

   Whether Mammoth will get any snowfall from that feature remains questionable as the plume may be just too far northward.   Models are suggesting some light precipitation, but not sure I buy it looking at the upper air pattern.   Snow might not happen again until there is some upper level trough and/or southward movement of the jet stream to push the moisture southward again.

   The current guidance says that could happen toward the end of next week with the models struggling about how much energy will be left by the time the front moves southward as they are indicating only weak troughing.  The GFS (image below) and ECM are both rather weak and keep the jet too far north for decent precipitation.

gfs_namer_228_

   The GFES ensembles (image below) are still rather mixed with a large spread, but the mean is farther south with the jet and the ECM ensemble is similar.  The general thinking is that there will be more snowfall toward the end of next week, but confidence is low on the details.

gfs_2016120612_spag_228

  Looking farther out, the GFS model (image below) has been rather consistent over the last several runs about a deeper trough developing early over the following week.    A pattern like that would produce big snowfall in the Sierra.  But I am not overly confident yet looking the ensembles that show that solution as an outlier with the ECM model showing ridging.  The CFS climate model hasn’t picked up on it either.  Hopefully the GFS is on to something as it does do a good job of picking up on “stronger” signals in the fantasy range.

gfs_namer_336_

   And that is the general issue in the longer range time scales.   The models are just all over the place.   The models have also not performed well in the longer time frames lately.  The latest ECM climate model did another 180 flip after flipping hard the previous run.   That doesn’t lend much confidence so climatology is the best forecast right now and that says storms happen at times in December.  WG

Posted in Mammoth Lakes Weather Forecast, Mammoth Mountain Weather Discussion, Mammoth Weather | Tagged | Comments Off on Powder Forecast — Tuesday December 6th, 2016