Seasonal temperatures with dry weather will continue through the work week with a splitting system showing up for this weekend…Big Amplifacation of the westerlies showing up Week 2……

Tuesday AM:
OK….some of my readers comments have not liked the Dweebs pessimism. So let me put this Winter into context.
This Winter will offer more of a challenge at distance to the forecaster because of the persistence of the west coast ridge. Persistent long wave trofing in the east that is stationary by wave length creates a long wave ridge over the far west. Sometimes the ridge is not so evident but it is there nevertheless. It invisibly shows up when storms split over the far eastern pacific. Often times the split flow only shows up within a 3 to 5 day period, and other times only within a few days before the energy moves on shore.  This is the challenge.  However, the whole winter will not be that way. For one, MJO will modulate the westerlies, cause amplification and retrogression and cause some exciting and possibly amazing weather patterns. In December, that may mean a Polar Outbreak over the far west which is something that has not happened in a long time. With La Nina and the QBO in the negative phase, I have seen very strong amplification of an Eastern Pacific ridge into the Polar regions near 140west that can dig very cold deep arctic systems over the Great Basin that can cause temperature’s in Mammoth in the single digits and lows to -20 in town! Then only to be followed by a break through of the westerlies underneath a GOF block that dumped snow in Mammoth, down all through the deserts of Eastern CA, Western NV including the Owens Valley.  December can be a wild month for this kind of winter shaping up! At this time, the Americans models are hinting at that. However, last nights 00z European deterministic model showed this highly amped ridge, week 2 as a block over the west coast, only retrograding slowly toward the 13th of Dec. So the Euro is dry at this time….

In the meantime, the medium range shows the next significant cold Trof for late this weekend splitting. Confidence in this storm to bring significant snowfall is dubious at best “at this time”……

For what ever it is worth, the GFS does bring some snowfall to the sierra later this weekend, however at the same time, the trof splits with most of the energy going south into Southern CA.

8:30AM Tuesday:

The news 12Z GFS is coming in now.  I decided to look at the upper jet structure to see what kind of dynamics there is with this system for our Geographic’s.  So here are the important points, regardless of the system splitting.

  1. At 500MB, the upper flow is split at 38N-140West at 12Z Saturday AM
  2. The air mass over the eastern sierra is very dry with the RT rear entry region of the upper jet well off the Northern CA coast.
  3. At 12Z Sunday, 700MB RH is only 30%, however the RT rear entry region of the jet at 250MB is favoring Central CA. ( So not a whole lot to get excited about without the moisture)
  4. However, BY 00z Monday (4:00PM) Sunday, A different branch of the upper jet at 250MB come into PT Conception and spins up over a 24 hour period from 100knots to 140knots. The Front Left exit region favors the Southern and Central Sierra Sunday afternoon and early evening. However, 700MB (RH) moisture is lagging at only 50% to 60%, good for at least light snowfall. Apparently, the best RH Develops about Midnight Sunday into Monday after the main jet slips south. Again the best forcing develops Sunday afternoon into the evening in a drier air mass vs 10:00PM Sunday (06Z Monday) during higher RH. Southern CA looks to get some rain out of this Monday morning……at least by this model run….

Stay Tuned….lots of moving parts, but over all, not an exciting storm for the Central Sierra…

 

PS:  GFS is trying to bring in some CPK air mass by mid December…..Burrrrrr!

 

As always…………….More later and I am not tied down by a news letter due three days out!!

 

The Dweeber…………………….:-)

Chilly Upper Low was exiting the Sierra Crest this mid-morning while wrap around precip began….a few more inches is possible this morning……Short wave ridging is on the move and will build over the top of us tonight for a fair day Tuesday…..Next possible storm this weekend….

No surprises this morning as storm worked out pretty much as the Dweebs planned. That is about 12 inches at the Main Lodge and about 18 to 20 inches over the crest. Amounts in town for the most part will be in the 3 to 6 inches range, give or take an inch or so…

Today weather reflects the upper circulation center exiting along the border of the Southern and Central Sierra with a short period of upslope today then clearing tonight. High temps today will be in the mid to upper 30s with lows in the teens and tomorrow a seasonal 44 degrees.  It will remain windy over the crest today with diminishing winds tonight. The next upstream system will split with no more than clouds, upper level winds and a little more cooling. Earlier there was some suggestion that a cut off low might form and remain off the Southern CA coast Wednesday.  That in itself would have no effect upon Mammoths Weather. However it might enhance the next upstream system possible for next weekend by adding some moisture to it.  At the moment, that system seem to be taking a more northerly path.

Pattern going into December for a week or two and beyond: (Winter Outlook)

Beyond next weekends storm, the pattern really amplifies with a very sharp ridge pushing up into the Arctic, near the west coast. In fact, there is so much blocking developing over Canada, the CONUS will have quite the cold stormy pattern developing. The central west coast looks pretty dry with only weak systems to watch.  We will have to wait and see where this ridge sets up at.  It may be a full latitude “top heavy” west coast ridge.

As a weather lover, I am not as excited about this winter as last from what I have seen so far. The biggest influence upon this winter over last winter is both the QBO and ENSO.  ENSO is in a little stronger La Nina mode and may become moderate at some point later this year.  The Quasi Biannual Oscillation has shifted negative as the stratospheric winds above the equator that were in the positive mode, “West to East” last winter, to the reverse “East to West” this winter. This will have a profound effect upon this winter by forcing a deeper PV Eastern Low further south. That usually makes for a more persistent west coast ridge at times, with a frequent -NAO and -AO. So more of the cold air drops out of the arctic to the east of us rather via the Eastern GofA and western Canada. Thus the West Coast is likely to have more frequent +PNA teleconnection patterns this winter.  The persistent strong zonal jet across the north Central Pacific is not likely to be a persistent feature this winter as a comparison to last winter.   About the only teleconnecting anomaly that is in our favor is the warm SSTA pool in the Bering Sea. If the Bering Sea was cool, I believe that we would remain ridged up more often than not, a good part of the winter.

The PDO is still in the cool phase, that argues for troughing along the west coast so there are some positive teleconnections that are working for us this winter.  However, the over lying base state of a somewhat stronger La Nina and the -phase of the QBO will be both fighting/weakening west coast storms more often than not for the “Central and Southern West Coast” this winter. There will be several storms that will split and weaken that will be forecasted to be stronger. As a result, This may not be as fun a winter to forecast from a distance, as long range forecasts will not be as reliable as compared to last winter.

 

The MJO will be our friend this winter as stronger phase space (RIMM) incursions from the Indian Ocean into the Western Pacific then Central Pacific will help to break down or retrograde stagnant, large scale blocky hemispheric patterns, that may develop for the winter of 2017/2018.

 

More Later………………..>>

 

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

While Strong High Pressure builds off the west coast today bringing near record warmth, the next system is now looking better for a more favorable track for precipitation into the Northern and Central Sierra….Weather to become very windy for the high country Saturday into Sunday….

Friday 8:30AM Update:

Main changes to the forecast for the weekend include the slowing of the storm, more emphasis of precipitation for the Central Sierra now instead of the Northern Sierra.  QPF for Yosemite is about 1.5 inches of H2O eq.  Mammoth Mountain is store for at least a foot of freshes over all. The upper mountain may experience some rain-snow mix with the onset of the storm’s precip Sunday. The freezing level is quite high at 11,500 at 10:00am Sunday, but will fall to 10,000 feet by 4:00PM Sunday. The snow level will be about 1000 feet below the freezing level. Expect precipitation over the upper part of the mountain will change to all snow during the afternoon Sunday while the lower elevations will experience most likely either rain-snow mix or very wet snow by late in the day….  The strongest winds will be Sunday.  These winds will be strong enough in some areas to cause some damage along the highway 395 corridor Sunday.   The colder portion of the storm will arrive for the most part after midnight Sunday with the freezing level crashing later Monday morning. Snow will begin to accumulation in the Town of Mammoth Monday morning with a plow needed during the day Monday. Between 3 and 6 inches is expected in the Town of Mammoth Monday. Highs in Mammoth Monday will be in the upper 30s in town.

Storm behavior:

  1. Storm will be moving into a record warm air mass,  Pressure gradients will be very steep and winds will be strong Sunday as a result.
  2. The trof will begin splitting Sunday with a closed center forming Sunday night well west of the Bay Area. The split will have the the effect of developing the bulls-Eye of precip further south over the Central Sierra. The closed center will come on shore over Monterrey and Mammoth will end up on the NE quad of its upper divergence. So Mammoth will greatly benefit from this change of the behavior of this storm. It would not surprise me if we got 1 to 2 feet on the upper mountain, but the forecast is for a warm storm 1st that will begin as rain on top of the mountain then change to snow within hours. The slowing of the storm and its closed center will allow a period of upslope Monday which will favor the Town with its easterly flow, and could prolong precipitation well into Monday.
  3. It will be much cooler after this storms passage with seasonal temps for Mammoth. Highs in the mid 40 and lows in the teens and 20s.

 

Longer Range:

Another splitting trof will effect the high country mid-week but will be dry. There is the chance that a closed low will develop from this storm off the Southern CA coast and become stationary, only to be picked up by a stronger Trof the end of next week…..Stay Tuned….the Dweebs got you covered………:-)

 

 

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Although the Thanksgiving Holiday will be much milder than normal with a late November Heat Wave for the southern half of California, the next storm system this morning is showing up to be a potentially better storm than what was indicated the past 5 days for the period Sunday through Monday. The upper jet’s right rear entry region now favors the Central Sierra later Sunday night into Monday morning and the QPF by both ECMWF and GFS has this system showing the potential of bringing significant snow over the upper elevations later Sunday into Monday night.  Additionally, both Global models the ECMWF and the GFS  are more in line with the storm coming through in two parts. The first part with feature a warmer system Saturday and Saturday night with strong winds and the second portion colder for late Sunday afternoon into Sunday night. The models are also consistent in showing the snow levels falling rapidly behind a strong cold front early Monday morning. Although this system is still some 4 to 5 days away, moderate amounts of (6-18 inches) are showing up as a possibility for the very early next week period by the two global models this morning.

Again the Dweebs want to emphasize that the antecedent conditions of near record warmth prior to the weekend will precede this systems arrival.  Thus, exceptionally strong winds are possible to develop Saturday into Sunday over the high country.

In the meantime, enjoy the beautiful holiday weather this week. Expect highs in the upper 50 to low 60s, with lows in the 30s Wednesday through Saturday with winds coming up Saturday and rain turning to snow Sunday through Monday AM.

 

Happy Thanksgiving to all from

Dr Howard and the Dweebs……………………..:-)