Forecast Models Throwing inside slider…..Strike 3 for the Weatherman….Big changes ahead…
Saturday December 31, 2016
Posted at 11:54 am by Howard
Its been interesting to watch the big mass of cold Arctic Air being handled by the forecast models. It is important to realize that it takes a reservoir of cold air to tap from over Canada for the pool to from. Keeping in mind that for the far west coast, which normally does not get this kind of cold air mass, even every 5 to 10 years of this magnitude, the pattern has to be especially out of kilter.
This year up to today, New Years Eve, has experienced a lot of the pattern of the -EPO and -WPO. The negative phase of the Eastern Pacific Oscillation (-EPO) is one where you have a big blocking high pressure system in the Gulf of AK. To get Arctic Air In January to plunge down the west coast, you need the Block to have strong legs as well! This means that it needs to be pretty much a full latitude ridge, just west of 140W and positive tilt as well. However, climo wise, full latitude ridges in January are not that common in this area. They are more common in December. The forecast has been one of tapping the polar vortex and pooling up some amazingly Cold Arctic air and plunging it south through at least Central CA. Temperatures at 10,000 feet (700MB have been forecasted to flirt with -20C for the middle of the new week for Eastern CA and Western Nevada.. That would be highs in the Town of Mammoth in the low teens and nights below zero for a stretch of at least 4 to 5 days! IE A real Pipe Buster! However, this is no longer as likely to happen!
There has been some real back peddling with the southward push of this frigid air mass of late, stalling it out over Northern CA and NW Nevada. To add insult to the weatherman and injury to his ego, the air mass will shift east pre maturely. According to both last nights 00z GFS and ECMWF runs, and now this mornings 12z GFS and European, this happens by Tuesday. An important point to make is that the 12Z deterministic run of the European is similar to the GFS, but is not as dynamically aggressive with the lead undercutting (Storm), that the GFS says will hit the sierra early Wednesday AM, the 4th of Jan. Both models handle short wave energy and the height field differently between Wednesdays storm and the Sunday Storm. This is of concern to any fair weather forecasted between systems. The Sunday (Jan 8th) storm into the following week is associated with a deepening (-WPO). This means that the block over the -EPO region will retrograde to the -WPO region or from the Aleutian chain, into the Bering Sea. The wave length suggests retrogression of the long wave Trof from 120 west to about 130 West, then positive tilt deep into the Subtropics. Thus a major “AR” event is possible about next Sunday into the following week. All Global models show it including the GFS, ECMWF and the Canadian.
So what this all means, is that the odds are, that it will not get as cold, but expect more snow, beginning as early as Tuesday night into at least Wednesday Night…..
Another model run or two with a consistent GFS and or European model run will give the National Weather Service the confidence to either go to a winter storm watch for either Tuesday night or Wednesday or a snow advisory. The Wetter GFS models is suggesting a few feet from the Wednesday Storm. The Sunday through Wednesday storm for the following week is currently showing up as a monster! …… The powder for the Wednesday system looks cold and dry but the platinum powder criteria is becoming less likely….
Dr Howard and the Dweebs…
I’ll have an update written tonight for your New Years Day Weather Letter…..