Archive for November, 2017

Friday AM Update:

Just has a peak at both the 00Z Friday EC and 06Z GFS:

Some interesting deterministic run possibilities….

Both Models continue the trend of the Blocking pattern with ridge in the west. And continuing their trend of the possibility of a bit more moisture for the weekend (Sunday) system for Mono County. I think that I covered it well in the late Thursday afternoon update below.

A new twist though showing up from last night 06z GFS run with some hang back energy underneath the building ridge early next week from the Sunday system. The GFS has this weak low left over or near Southern CA that may just provide an off shore flow and a warm up for LA. However, the ECMWF has a bit more energy that follows the Sunday system early next week that spins up a small closed low on its drack south then off the coast of Paso Robles, CA. That would dampens LA’s warm up and actually put Mammoth in the upper Divergent NE quad of that system, providing some light snow or snow showers anytime between late Monday afternoon and Tuesday night. The system does track south off the SO-Cal coast and so the off shore flow is probably just delayed in this case.  An important point to make is that this all happens as the upstream building ridge that will eventually take over the west coast, later Wednesday into Thursday.

Some New Twists to the longer range:

Earlier in the week I mentioned that the ridge that will be building next week will be top-heavy. This means that a lot more high pressure aloft (Anomalous higher heights) will develop over the higher Latts, and eventually over AK.  +(PNA) & (-EPO). That in its-self reinforces the pattern that has the potential to deliver very cold weather to the Ohio Valley and south to the Gulf States in the 6 to 10 day period. The EPS, AO has that teleconnection dropping to -3.5 standard deviations of normal, meaning that this Block has legs and will likely hold through the 10 or 12th of Dec. However, both EC and GFS are showing some changes there after as the AO goes to 0 (neutral) by the 18th. The WPO area (Bering Sea) has increasing heights at 500MB between the 14th and 18th of Dec. This is signaling a change with the possibility of retrogression of the upper west coast block allowing CPK air (continental polar) air mass to back up over the far west. (Cold)  More later…….

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I Just looked at the last few runs of the GFS and EC (American models) and Euro for the weekend. The Trof that is forecasted to come through this weekend is holding on to a WSW flow better in the GFS as compared to the ECMWF.  This is being reflected in the Models QPF.  The EC just brings us a dusting while the GFS suggests possibly 4 to 5 inches of snow over the crest, out of .3 to .4 inches of water.  The 18z GFS is showing higher QPF amounts as compared to its previous runs.  What ever we do get, the ratios of snow to water is going to be pretty high. Possibly 13 to 1.  So some light powder to begin the new week. This will be a windy system for the upper elevations and breezy for the resort levels. It will also be a cold system with temps at 700MB (10K) lowering to -8c to -10C on Sunday. Not all that unusual for early December.

Long Range:

I have beaten this dead horse enough so I will leave it alone for a while and concentrate on the Inter-seasonal outlook.

Today the ECMWF EPS 46 day weekly’s has updated. All I will say for now is that its long-range teleconnections are encouraging!

Here is a brief summery of what I have found out.

1. The Current negative phase of the Arctic Oscillation turns Positive after the 18th of December and trends more than 4 standard deviation’s above normal by January 7th. So Lower pressure develops over the Arctic which can lead to a more progressive flow across the CONUS. (US) At the moment we are headed toward a very blocky pattern across the CONUS next week with a -AO. This is usually dry for California in a La Nina.
2. In the same time frame, “Early January to mid Jan, the EP turns very negative, meaning a strong block over Alaska. A strong block over AK with a -AO is dry for California. However, a +AO with a -EPO could be wet for the West coast. The PNA which is positive now will trend negative between Christmas and New years,  while the WPO become negative IE (Blocking over the Bering Sea), toward the end of the year. This suggests Trofing along the west coast toward year end, and a block over the Bering Sea could be a wet west coast pattern. These teleconnection patterns work together and offer various solutions.  My sense is that we will begin to turn stormy around Christmas with several  period’s of snowfall up to about mid of January.  I am just using teleconnections, but that is all I have to work with at this time.

Dr Howard and the Dweebs………………….:-)

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…………………….:-)