Active Weather Pattern returns as Cut Off Low Season Begins…..Approaching Upper Trough cuts off this weekend to our south, bringing upper divergence and storminess into early next week…..

It’s Cinco de Mayo and Cut-off low season has finally begun.  Current upper ridge that brought low 70s to Mammoth and 90 to Bishop on Thursday has shifted east to the Rockies. This is a full latitude ridge that extend from Northern Mexico to Canada. To our northwest is what appears to be the first is a series of Trofs that will migrate through the west coast.  Some will be progressive and others will become Cut-Off Lows. This will be a challenging pattern for forecaster’s, as mid springtime storms unlike winter storms play by a different set of rules. “CAPE” Convective Available Potential Energy will weigh in heavily with each stormy period now as the Sun’s angle is Summer-like in the western sky.

As our Western Trof approaches today, winds will increase blowing off any convection well into Nevada. By Saturday mid-morning, the Upper Trof is along the west coast with a closed low forming just west of the Bay Area. Southerly flow is increasing over the Sierra as moisture advects in from the south.

During the afternoon on Saturday, the upper center “spins-up” with increasing upper divergence in its NE quadrant. This begins the process of dynamic lift over the Central Sierra along with increasing chances of precipitation over the Mammoth Area. Expect Towering Cu and thunderstorms forming with rain, possible hail, thunder and of course snow over the higher elevations. The snow level will fall over night Saturday night in the Town of Mammoth. Light accumulation’s are expected.

As the upper low moves inland over Ventura County Saturday Night, SE flow will push precipitation up into the Owens Valley.  Up-Slope Flow and precipitation is expected along the Eastern Slopes of the Sierra later Saturday Night into Sunday.  Upslope precipitation may continue through Sunday and possibly Monday at times.  It is uncertain how long the upslope flow along the eastern slopes will continue, as the timing is dependent upon the cut off lows SE exit. This is currently progged the early to the middle of next week. The next upstream system should give Mondays Cut-Off the boot by mid-week.  Forecast models are showing any ware from 6 to 12 inches of snow over the sierra crest by Monday.  The extended outlook shows on and off  unsettled weather with cooler than normal temperatures, as high pressure aloft builds over Alaska in the longer range…

Teleconnections from the ECMWF and GFS show trending -EPO and -WPO the next two weeks.

Thus the Storm track will likely remain suppressed into California.

 

Dr Howard and the Dweebs……………….:-)

As the Fishing Opener has come to a close……Warm Sunny Days are here to stay…At least through the middle of this week….A change in the pattern highlighted by a developing “Cut-Off” low will bring the chance of showers and thunderstorms, with the chance of showers beginning as early as this Thursday through the weekend and beyond.

Its been a beautiful fishing opener, with light breezes over the lower elevations and bright sunny days.  Temps on Sunday topped out in the low 60s while at Crowley Lake, it hit 70 degrees on Sunday. The upper ridge off shore will actually build into California late Tuesday into Wednesday, then shifts east into Nevada Thursday. Because along the western periphery of the upper ridge, we have southerly flow, we get one more day of warming Thursday.  Highs will be close to 70 in the Town of Mammoth.  However, like during the summer, once the upper ridge shifts east, our air mass becomes more unstable with the beginnings of cooling aloft. Towering cumulus just like during the Summer in the afternoon will develop with the possibility of diurnal afternoon and evening showers.  Remember, the first week of May is like early to mid August with the high angle of the Sun.

Following the upper ridges passage, is an upper trough. This trof is progressive and will move to the west coast by this Friday morning. Strong gusty southerly winds will increase over the upper elevations as the rear right entry region of the upper jet approaches. This will destabilize the atmosphere even more continuing the chance of showers. It will be cooler Friday through the weekend with the chance of showers each day and evening. Note: The showers look mostly convective and thus diurnal in nature.

More on next weekends storm:

The upper ridge is forecasted to sharpen up as it slowly progresses east to Eastern Colorado this Saturday, then stalls out. This forces the upper stream trof over California to become Cut-Off from the westerlies. So this is our first cut off low of the Spring the weekend of the 6th.  Cut off lows are very unpredictable and at this time, it is not uncertain where the cut off will develop. For what it is worth, all the forecast models today Sunday afternoon, are trending more toward a stall out along the coast of California as the cut off tracks very slowly SSE. This low may be with us between the upcoming Saturday through the following Wednesday and possibly beyond. This will prolong the possibility of showers and thunderstorms each and every afternoon and evening until it exits.

More later this week…..

 

Dr Howard and the Dweebs………………………:-)

Blustery Northwest Jet will keep weather unsettled this week with cool windy showery weather…….Warm-up expected by the end of the weekend….Longer range shows a nice warm period beginning the first week of May….

For the Dweebs, this is my least favorite time of the year.  It is the transition season between Spring and Summer with the northwest jet prolonged through Northern and Central CA. The Jet is tilted NW/SE as a long wave upper high inside of 140 west is too far off shore to bring warm temperatures and too close to California for any major storms. The front right exit region favors the sierra with “Wave Clouds”, so you wave cloud photographers, will have the opportunity for some good shots this week in the early AM hours and late afternoon mostly areas east of Highway 395.  The NW jet with its front right exit region over the central sierra favors convergence aloft in this sector. Downward vertical motion results in strong winds at times aloft and mainly orographically induced snow showers. 

It will be quite breezy to windy over the upper elevations on Mammoth Mt most of this work week.

There will be nuisance snow showers this week, mainly Monday through Wednesday morning. However, the showers will not add up to much of anything.  I call it nuisance weather!  But it is necessary to get the season along before summer finally hits in June.  Expect highs in the 40s and low 50s with lows in the 20s and 30s.  Winds will Crank at times to 80MPH over the crest with gusty winds in town as well.

Will there be one last storm before summer hits?

Maybe more than one….

I just had a peak at the European Ensembles for week two. (next week) It shows; 1st,  The sharpening of the upper ridge off shore without the progression of it into California. This argues against any big lasting warmup. It shows a cold low dropping SW from Alberta Canada on the 1st and settling in over the Western Great Basin on the May 2nd.  There after, retrogression takes place with the next short wave dropping south down the west coast. Meanwhile, the upstream ridge retrogrades west and builds up into Alaska, (-EPO) style.

So here we go again!!  Remember, this is the Euro, not the GFS.

 

The Climate Models CFS climate forecast system suggest that the 3rd week of May will be colder than normal with the chance of snowfall.  No telling how much though.