A Transition to a Very Active Pattern by Mid Week is Expected as the nose of a 180 Knot Upper Jet extends to Northern CA by Mid Week……Multiple systems are expected periodically for the Northern and Central Sierra……
Saturday December 5, 2015
Posted at 2:16 pm by Howard
I have had a lot inquires in regards and concerns about when will the big rains will come to Southern California. The Dweebs want you to know that we are watching the models carefully for signs of when that may begin. The new GEFS has been implemented and it a beauty! It’s like buying a new car! 😉
So-Cal folks keep this time in mind…..
The ensemble really amplifies the pattern 10 days out while keeping the Great Basin in the Cold. The models suggest that this ridge will build northward north of Hawaii and become Cut off over Alaska while a rich plume of PWAT imbedded in an atmospheric breaks underneath, and heads for Southern Ca. The model shows an AR knocking at your door just prior to Christmas Day……..Remember this is a long way out and so lets see how this Ensemble Model does……
Tuesday AM Update:
Good Confidence in the upcoming Thursday Winter storm. High winds expected early Thursday AM…..Good warm sector with initial high snow levels. CRFC has freezing level at Yosemite, 4:00am Thursday at 10,500. As the air-mass moistens up, evaporative cooling will initially allow snow levels to fall below the usual 1500 ft difference between the snow level and freezing level. So the snow level may bounce around between 7000 and 9000 feet. By 10:00 AM Thursday we should be saturated and the snow level as solid 7000 to 7500 feet. Latest QPF for the crest is close to 2.00 storm total by late Friday afternoon. Some of it will be at 8:1 and some later in the storm 12:1 to 13:1. Orographics come in to play so odds are good for at least 1 to 2 feet with up to 30 inches in Saddle Bowl. The outlook for the weekend shows Saturday the break between storms…Although there could still be some snow showers….
Just a quick comment on the Sunday/Monday storm: The Tuesday 12Z GFS shows a track more like the 12z ECMWF Monday/Tuesday model runs. So it is not as wet as earlier runs of the GFS. Nevertheless, expect at least a foot out of this one. It may not be platinum powder, but plenty fluffy! The storm is a quick intense hitter Sunday afternoon and Night with showers on Monday. The following system (mid week) is a cold inside slider type with snow showers possible. Week 2: expect a 60% probably of being wet for most of California. The upper flow becomes more zonal. CPC is putting more faith in both the Canadian and GFS ensembles rather than going with the ECMWF solutions which show higher Heights and a jet further north……for the time being…..
As Another Comment….
The GFSX has a series of storms following the Thursday/Friday system fairly close to the coast. The main cold pools move inland between Mammoth and the Northern Sierra. This is a track that is not favorable for major precipitation for Southern California. The Dweebs will update later this week…..
Confidence is increasing that the first storm cycle of the Winter will begin this Thursday as a series of weather systems head for the Central Sierra. The first storm has a light to moderate AR attached to it with a PWAT plume of 1.25 inches. So there will be a moist warm sector that will precede a colder portion of the storm. At the moment, WPC’s 5 day QPF shows 3 to 4 inch’s of Water EQ for the Central Sierra over a 5 day period. About (3 feet of snow over Mammoth Mt). However, most of the precipitation will fall over a 36 hours period. This storm is likely to have a wind event attached to it Wednesday night into early Thursday AM, so travel in the Mono County area Wednesday north and south along the 395 Highway is best before mid to late afternoon. The Snow Level will probably begin around 8000 ft early Thursday AM, falling rapidly by mid to late morning….. Heavy snowfall is expected Thursday afternoon into the night……
A following storm will arrive later in the weekend. That one looks colder with possibly higher snow to water ratios. The new 12z Monday run of the GFS has that system trending to dig further south and west, and so it may actually be the first significant winter storm for Southern CA and their Local Mountains, if that trend continues. I will take another look at that Mid-Week after several more runs…..
Dr Howard and the Dweebs…………………………….:-)
Although the Dweebs are still waiting for the more classic El Nino forced North American pattern to develop….A series of Winter Storms look destined to slam the Sierra from north to south beginning about Mid Week, next week.
So far the most obvious signal usually associated with a strong warm ENSO Winter has not yet developed. This is why Southern CA remains dry. Sensibly, you will know when that change occurs, when the storms come from the West/North West at Mid latitude. Additionally, it will be noticeable, as the presently located fire hose (jet Stream) shifts from the Pacific NW, south to much of California. The upper jet will split out over the Pacific with a wet southern branch into the Golden State. The Dweebs would expect higher pressure over Western Canada and the Gulf of AK, and Lower pressure well south of the Gulf of AK aimed at California. So more time is needed, especially for Southern California.
Currently the storm track remains to our north….A west to east upper Jet at 300MB is expected to sag south mid-week and port into Northern California. The pattern will be preceded by high winds over Mono County. Over the following days….The jet sags south and the Central Sierra receives heavy snowfall. Amounts through Friday AM are not super heavy but between 1 and 2 feet is certainly possible. The Dweebs will update if that changes. The pattern change will be highlighted by the fact that the nose of a 180 knot jet will port on shore over Northern CA with the front Rt exit region effecting Mammoth in the form of strong winds beginning late Wednesday then ramping up that night into Thursday AM. No doubt a High wind episode is very possible for Wednesday night or Thursday. The upper jet is expected to sag south through the Bay area and Mammoth later Thursday allowing the southern sierra to benefit from precipitation. However at this time, Southern California apparently will miss most of this storm, unless the longer range models do something different.
There are subsequent systems in this pattern destined for California. So another storm is possible sometime that following weekend.
One thing seems likely……The snow will be accumulating up in the Sierra! Some of the guidance suggests up to 5 feet of fresh over the next 10 days on Mammoth Mt….
More updates coming next week or sooner if necessary….
Dr Howard and the Dweebs…………………………:-)