Upper Low Now Moving South through the Pacific NW will increase breezes this afternoon with a upper winds becoming easterly by Sunday….Some light snowfall expected……Warming trend later next week with the eventual return of low 70s by next weekend end….

The Forecast models are in good agreement in bringing a closed upper low south from the Northern CA coast then SE along the coast line or just inland over Ventura County. It then is expected to shift east Monday….

The majority if the precipitation will be over the Southern Sierra Near Mount Whitney.  Over a foot of snow is possible there. The other area that is under the gun is over the White Mountains and the mountains around Death Valley.

Closed lows of this type are difficult to predict, precipitation wise, as there is not a true active front that comes through. It is rather an area of surface, mid or upper level convergence called a deformation zone that will come through Mammoth Sunday morning, and part of the afternoon. This deformation zone will shift south with time and may stall out over the southern sierra. Where it stalls is the area with the most precipitation expected. In this case the upper low is forecasted to shift east through the Mojave Desert and so the deformation line will slow and pivot over the Southern Sierra and Owens Valley.  Mammoth should receive at least 2 to 4 inches of Snow, Sunday into Monday at and above 9,000 ft.

However, this system has a convective element to it,  and should a thunderstorm develop over night or in the Morning, several more inches is possible; even at lower elevations.  Otherwise, over the lower elevations 7000 to 8000 feet, there will be snow pellets and brief snowfalls possible.   For those in the back country, be prepared for cold wet conditions with at least a light snowfall, in the 2 to 6 inch range.

 

Dr Howard and the Dweebs……………………………….:-)

Mid Latitude Trof Spreads Subtropical Moisture into California with showers expected by late morning and into the afternoon….Snow Level is above 10,500 feet……Clearing Friday then fair Saturday AM with the next system colder with the potential of several inches of snowfall above 8K Saturday Night into Monday Night…

Thursday Afternoon Update:

Just saw the finished run of the 12Z Thursday ECMWF.

It is remarkably in step with its previous runs and preferred over the 12Z GFS for that reason.  The Dweebs are not sure why the GFS is taking the upper low down the coast to LA Sunday night and Monday. However, the Dweebs are not buying into it.

This is actually a better storm for Mammoth in which the QPF will bring higher snowfall amounts.  The upper center is located near San Jose Sunday at 5:00 AM. It then remains quasi stationary for about 12 to 24 hours before heading SE right down the interior of California, then exiting out to Arizona crossing the Colorado River, Tuesday afternoon. So Sunday and Sunday night some good convective snowfall possible above 8K, then some possible upslope as the low provides some backwash, as it moves out of the San Joaquin Valley into Kern County Monday evening.

As a note, to back country travelers,  I can not emphasize enough for the folks that are not experienced “winter” back country travelers, to postpone until the middle of next week….  It will be cold, wet, snowy and miserable, late Saturday night though at least early Monday….  The Dweebs will come out with an estimate of snowfall for the Sunday/Monday period on Saturday Afternoon.

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Skies continued to be cloudy Thursday morning with SFO Radar showing an active front from Santa Barbara to Fresno to Tahoe…..shifting eastward. Rain showers a good bet later this morning and afternoon with a few embedded TSRWs. The more important story is the Colder closed low that will wind up as it drops out of OR, and spins up along the Northern and Central Ca coast Saturday and Saturday night. The NEW 12z GFS has the closed low dropping further south now down to the Channel Islands by late Sunday night and as far south as Catalina Island by Monday Night. This is much further south and west than both the 00Z Gfs and ECMWF showed. Additionally, it has plenty of time to generate a lot of moisture over a 24 hour time frame.   The big issue now is that if this track is correct, the storm will have significant upper jet energy over the very warm waters off the Southern CA Coast that is some 75F degrees.  The diabatic heating  off the warm SSTs, off the SC coast could make for some Severe Weather as it swings inland Monday night and Tuesday AM for Southern CA. the Dweebs will update this afternoon to see what the 12z ECMWF show with the track as well. As a Caveat….This new track is a big departure from last nights run…

Potentially…this could be quite the rain and snow producer for the Southern Sierra south, depending upon the track.  Stay Tuned!!

 

Meanwhile, the east coast of New England looks to dodge a bullet as the new gfs takes the track of Joaquin more in line with the ECWMF. Wow! what a model the ECMWF is!    It blows our GFS away at a distance!

 

the Dweeber………………………..:-)

Wrapping up the Month of September and being retrospective..it has been a real warm one……Our first either inside or outside slider will make its way through Northern and Central CA Sunday…..Showers and possible snowfall is expected….

Wednesday AM:

  1. The 06z GFS has a better organized but small system ejecting through Central and Northern CA. There is plenty of moisture for it to interact with.  The models generate between .25 and .35 over Southern Mono County Thursday with a freezing level of 11,000 feet.  In that it is convective, a snow level down to 9500 would not be unreasonable. So a few inches of snow is possible over the higher elevations Thursday.  Expect clearing weather by Friday AM. High Temps will cool to the low 50s Thursday with 30s possible by morning…

2. Continuing with regards to the new model runs from last night. As indicated yesterday, the ECMWF has been pretty bullish in dropping a small compact deep closed low over California’s interior with its primary effects to be light snowfall Sunday. The system has small but chilly cold pool as indicated below in yesterdays discussion.  The model’s run was pretty consistent on this.

3. It is the 06z GFS that is struggling to get a handle on the same system.  Last night’s run drops the same system south over the pacific NW then as far south as Northern CA where it stalls it while it’s upper jet energy phases with an upstream upper low directly to the west. The 250UA jet prog develops an upper jet across Central CA with has implication’s for better QPF but a higher snow level, Sunday into Monday. The fact that the ECMWF drops the low south from Northern CA to about Fresno may mean that we may see a hybrid that combines the west to east upper jet of the GFS with a deepening upper low like the EC thus eventually creating a more cyclonically curved upper jet over CA with time. The snow level would end up higher but the QPF higher as well between Sunday and Monday. The screaming message here is that if you are in the back country between late Saturday night and Monday, you should prepare for the possibility of a winter storm capable of producing 6 inches to a foot above 8500 to 9K feet. This is not a forecast just some possibilities…..

 

Mote later….

 

Dr Howard and the Dweebs………………………………..:-)

 

 

Current Analysis and days 1 and 2 progs show a continuation of the moist mid and upper level flow over the Central Sierra. Even my wife Donna mentioned to me that she observed Virga over the weekend. Several spotters from the NWS Hanford reported some sprinkles Monday as well.  The flow is out of the Tropics in the super heated Nino 3.4 region. Upper divergence is no doubt playing a role associated with the Positive tilt trof centered west of Northern CA that will make its way inland Thursday with a slight chance of showers.   This is not a big deal, but this pattern occurring about 2 months from now would be.  Current mid latitude pattern is NOT being driven by ENSO…Just mid latitude forcing…Heights are pretty high with this mid latitude upper low and so it remains pretty mild with the high temperature over Mammoth Lakes Monday at 70.  By the way…Fall colors are in full spectrum at elevations above 9000 to 10,000. They are coming on over the lower elevations between 7200 and 9000k as well.  However, we are still a good week or two before they really are going strong over Mammoth.

 

Looking ahead:

The Euro has been toying the idea of an outside slider for CA the past several days and is holding on to the idea today. The GFS which does not have quite the resolution has been toying with the idea the past several day on and off.   This mornings 12Z GFS run showed an inside slider type system making is way down from the Eastern Gulf of AK

Here are some note worthy’s:

  1. 12z Tuesday GFS 500MB temps over Mammoth Sunday Evening  -15C
  2. 12Z GFS 700MB temps over Mammoth Sunday evening  +2.5C
  3. ECMWF 500MB temps over Mammoth Sunday Evening  -19C and -2C at 700mb.
  4. This is a big difference and a big deal for the North Central Sierra Sunday morning!  The current track of the ECMWF is more west!  The QPF has gone Hog Wild with over 2 inches of precip for areas like Amador County as they are in the NE quad of the upper low.  If this system takes a track further south and west, it will be a big deal for Mammoth Lakes and Tioga Pass as well. As it is now, we could get a few inches of snow above 8,000 feet “IF” this model verifies! It is too soon to be sure through…stay tuned….

Comments:

The positive SSTA’s along the west coast continue to be impressive.  No doubt they will affect the over lying atmosphere Diabatically.   Once the Deserts cool off later in October, it will be interesting to see how the west coast ridge sets up again and how the blocking will be with the RRR. This may delay the rainy season. Well See….