Powder Forecast — Friday March 3rd, 2017

Friday March 3rd, 2017

Ted Schlaepfer CCM  —- Mammoth Mountain WeatherGuy

Forecast Summary:

 Dry weather ends Saturday evening with snowfall increasing overnight and into Sunday with light and dry snowfall of moderate intensity expected all day Sunday before ending Sunday night.  Dry weather then returns Monday and likely lasts through most of Thursday with just a slight chance for a dusting overnight Thursday and into Friday.  Snowfall could then return by late over the following weekend and into the following week with a chance for storms at times through the 3rd week of March before storms may taper off end of month.

Next update Tuesday 3/7

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 3/4 = 0”

Sun 3/5 = 5 – 6” (H2O = 0.50” – 0.60”) **4

Mon 3/6 = 10 – 14” (H2O = 0.75” – 1.00”) **4

Tue 3/7 = 0”

Wed 3/8 = 0”

Thu 3/9 = 0”

Fri 3/10 = 0 – 3”

Sat – Mon 3/11 – 13 = 3 – 12”

March Snowfall = 0”
March Forecast = 70 – 90”

Seasonal Snowfall = 510”
Seasonal Forecast = 600 – 625”

Detailed 5-day Snowfall Forecast:

Sat 3/4 — No snowfall expected during the day, then light snow could start during the evening and continue overnight before increasing near dawn, accumulations 5 – 6” by Sunday AM, ~9” up top.

Sun 3/5 — Snow expected during the day and into Sunday night before ending by dawn Monday.  Riders of the storm day, accumulations 10 – 14” by Monday AM, 18”+ up top.

Mon 3/6 — No snowfall expected.

Tue 3/7 — No snowfall expected.

Forecast Discussion:

Short Term:   

    The satellite image from earlier this morning (image below) shows a deep upper level low pressure system moving southward from the Gulf of Alaska and a high pressure ridge currently over CA edging eastward.   The low and associated cold front will continue to move toward CA over the next 24-48 hours.

   The models as shown by the ECM model below move the upper level trough into the Sierra Sunday with very cold air filtering into the Sierra backed by the polar jet (blue arrow).   Orographic lift will initiate snowfall Saturday night and then the cold front moves into Mammoth by dawn Sunday followed by a post-frontal trough Sunday afternoon that should be laden with lots of open cellular cumulus clouds that produce the best quality snow.

   The 12Z GFS model backed off on the QPF for Sunday (image below) from over an inch and a half to around an inch with the latest ECM model down from 2” to around 1.5” while the Canadian is closer to the ECM model.   Looking at the upper air pattern, I think the wetter models make more sense as this will be a deep and highly dynamic low pressure system.

   It will probably get windy overnight Sunday and through Monday morning that will result in lift closure and weather holds, but hopefully there will be some terrain open Sunday to take advantage of the quality dry powder as snow levels will get down to below 3000 feet by Sunday afternoon.  Snow ratios will likely be in the 15:1 range Sunday PM.

   Snowfall ends Sunday night as the trough progresses quickly eastward and the jet stream lift northward.   Models say high pressure will build into CA Tuesday (image below) that will push the jet stream farther northward into the PacNW through at least Wednesday and most of next Thursday.

 Long Range:

   The longer range pattern is more complicated with models not in great agreement for the latter part of next week and beyond.   The GFS model seems to be doing better than the other models lately in the 6-9 day time frame as the ECM model has struggled as of late.

   The GFS keeps a trough of low pressure in British Colombia and PacNW late next week and moves a trough in the circulation into the PacNW late Thursday or Friday (image below) with a weak front brushing NorCal.   That would just mean clouds, some breeze, and maybe flurries in Mammoth during its passage early next Friday.

   However, the key to the forecast end of next week and beyond will be the exact strength and position (green arrows) of a blocking high pressure ridge near the Aleutian Islands and Bering Sea.  If it edges slightly southeastward toward the West Coast, we get wetter, as it will push the downstream trough farther southward into CA.   If the ridge moves towards Siberia, it will lift the jet farther northward into the PacNW and the subtropical ridge from Baja for drier weather.

   This whole set-up is similar in geometry to the first part of February except the blocking ridge is not forecast to build as far eastward into the Gulf of Alaska nor is the low pressure system south of the high as deep/strong and thus the jet stream may remain farther northward into the PacNW.  That pattern in early February was not forecast well by the medium range models in the 6-10 day range and the ridge was much weaker along CA and jet ended up being farther southward into CA.

    That pattern also had an AR associated with it resulting in rain on the mountain up to 9K before heavy snowfall returned around the 10th when the upper trough swung inland.   There will be an AR in the central Pacific end of next week, but it currently is not expected to get entrained into the weaker westerly flow.

   The bottom line is the forecast for end of next week and early part of the weekend could change again to wetter if the models aren’t handling the block properly.   The key to where the block forms and intensity will lie in the tropics and convection associated with the MJO which is generally not forecast well in the longer time frames.

   Nonetheless, the GFS model (image below) swings the upper trough inland (similar to Feb 10th) for a good snowstorm starting around Sunday and lasting into Tuesday March 14th.   Still way too far out for good confidence, but atmospheric repeating has been the trend this winter with a similar pattern having also occurred in early January.

   The long time frame GFS ensemble pattern (image below) keeps the blocking high positioned in the Aleutians and a trough downstream in the Gulf of Alaska through mid-month.  That would mean a progressive parade of storms in the PacNW with the question mark being how far southward these low pressure systems will move for snowfall into Mammoth.

   The CFS climate model (image below) and ECM climate model both suggest the longwave trough will remain near or along the West Coast through the third week of March.   That supports the idea stated above of a progressive pattern of storm chances every few days and maybe not a large scale significant storm cycle.   Think 1-2 footers every few days over a couple of weeks instead of 7 feet in 5 days.

    Overall, looks like March won’t be as big as January or February with a storm track generally farther northward overall than those months.  Monthly snowfall is expected to be slightly above average (average is 60-65”) with most of the snow falling around mid-month or just thereafter.   WG

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