December 15th:

The general trend of the models are to weaken the west coast ridge in the coming days and bring cooling and wind to the upper elevations. Although the upper ridge does strengthen early next week. It will not be to the point where it has been as there is another shot of cooling coming Mid Week. The big changes from the past few days in the outlook deal with the Christmas weekend where an inside slider type system affects the far west along with a closed low off the coast of Baja. This continues the dry pattern for the Central Sierra now until after Christmas. Of other concern, is  another opportunity later next week for another very significant Santa Ana wind event for Southern CA.

In general, the models are not handling the transitional pattern change that is upcoming very well at all.  The global models are continuing to flip-flop on the important details. They are not in sync with each other as well. Thus at the moment, long-range confidence in any specific solution is very low. The most that can be said is that it will be cooler in the coming days, breezy or windy at the upper elevations with a few period’s of light snow showers.


The Dweeber……………………….:-)



The Dweebs are beginning to see a trend in the Models that may bring a very Cold, “Even for December” air mass to the Eastern Sierra. This is proposed now for the weekend prior to Christmas Day..  In an earlier Discussion’s back in November, I wrote about the possibility of a major cold wave this  December for the Eastern Sierra with “CPK”  “Continental Polar” backing up from Canada, southwestward over the Eastern Sierra.  I reasoned this because of the proposed developing Meridianial  flow in the upper jet, usually associated with La Nina in combination with the negative phase of the QBO.  Over the past few days, the ECMWF has been becoming more consistent with the retrogression of the Eastern pacific ridge,  (due to the MJO going from Phase 7 to Phase 8).  The EC has the formation of a highly amplified upper ridge, currently along the California Coast backing up to about 140 West. The location of this highly amplified ridge is critical to the short wave track and cold 500mb-1000mb thickness pool over the far west.  If the upper ridge axis is a little too east, the track become a bit more east and we miss the exceptional cold over the far west. The GFS model has this ridge axis about 137 west….Too far east at the moment.  So confidence is based upon the Ecmwf being the best model at distance.  The Dweebs will follow the trend, as the trend is our friend…:-)

The bench mark for cold here in the Eastern Sierra over the past 40 years occurred 19 years ago, over the 19th, 20th and 21st.  The Morning of the 20th was the coldest aloft and Dec, 21 and 22nd over the valleys. However, surface antecedent conditions were different then, than they are today.  In the December 20th, Scenario, there was snow cover to lower elevations over Eastern CA, east and north over much of Nevada.  So there was a feed back system or at the least, less potential modification to the on coming frigid air mass.

According to the GFS Reanalysis 500MB charts as well as 500-1000mb thickness, from December 12z 19th, 1990 event, GFS 500MB heights were 513dm along the OR/WA border. The 00z 20 GFS had 515dm at the corners of CA, NV, OR.   By 12Z on the 20th, 500MB Heights were 518mb, so you can seen, there was very little modification that occurred on upper low pressure systems track SE.  According to the 500mb-1000mb thicknesses the morning of the 20th, the thicknesses were indicated to be about 516 just on the west side of the crest near Mammoth Mt.  I recall the thicknesses of 511 near Mammoth AP on the Nested Grid model (NGM). The high temperature that day was 6 degrees and the low at my home, then on Ridgecrest Dr was -12F. I did go down to the Forest Service recording site, east of the corner of Old Mammoth Rd and Main Street later that night of the 20th. I Peered into the instrument shelter, and it showed   -23F below 0.   This is the coldest temp I have experienced in nearly 40 years, living up here. It gave me a new meaning of cold.  The days that followed, were highlighted by frozen pipes all over town as well as all over the Eastern Sierra. When the weather warmed up, flooding from broken pipes were common.  PS. Even Bishop CA got down to -8 a few mornings after and Bridgeport was colder than -30F as I recall. PPS; it was the coldest Night of Lights, then at the Main Lodge, before it was moved to Canyon Lodge. (Fireworks show)

Although it is very early in the forecast game, the forecast progs are not as cold with this system as the Dec, 1990 pattern “at this time”…  Nevertheless, any extended period of below freezing temps, day and night for 5 to 7 days can create a big problem in town.

Another possibility; It is possible that this cold upper low digs west off shore. Unless that happens off the Northern CA coast, A major storm would be likely well to the south of us.