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…………………….:-)