Archive for December, 2012

More rippen and tearing for the weather system coming in Wednesday…..Weather turning much colder in the days ahead…..”Is Another Atmospheric River event headed for Ca again??

Because of the critical wave length of the long wave features; both upstream over the eastern pacific and down stream across the CONUS, the upcoming short wave coming into California, will split off shore…with a significant amount of energy driving south down the coast. What is critical for the Central Sierra is how close will the system get to the coast as it tracks southeast….And how much upslope will Mammoth get.

The results of the wavelength will cause the storm to split, and thus:

1. Force a lot of the precipitation over the Northern Sierra which is a change from yesterdays thinking.

2. Cause the weakening of the cold front as it moves south through Mono County.

3. Cause a closed low to form over Central Ca at 700mb which forces quite a snow storm Wednesday night and Thursday AM in its NE quad for Northwestern Nye County, Nevada!

4. At 300mb, the RT Rear entry region of the upper jet favors Southern Ca. and Northern Baja/NE to AZ and Southern NV. The upper jet actually couples with the subtropical jet for a good shot of precip for NW Mex.

The Dweebs feel that light amounts is the way to play it for now, in the Mammoth Area with .3 to .4 inches of precip for the crest. So we are looking at a system that will bring 1 to 3 inches in town Wednesday from the weakening front and a bit better amounts with the 700mb low Wednesday night for about another 3 to 4 inches. In this type of system, the upper elevations may get not much more than the Village. And….this is the kind of storm that may not give us much of anything. so if we do not get much more a a few inches do not be too surprised. The good news is that what ever we get will be the cold powdery snow that we like!

Because of changes in the long wave pattern and retrogression….the Dweebs are becoming more disenchanted with the Sunday storm. So although officially…the NWS is expecting more snowfall…the current model runs are doing a lot of Poo-Pooing on amounts……A consensus now between the 12z EC and the GFS has the Sunday/Night system an inside slider.

Will update on this tomorrow…….We may end up with even less then the Wednesday/NGT storm.

 

OUTLOOK:

The Dweebs feel that once retrogression is underway again, and the wave length adjusts over California, we may get into a wetter pattern that will favor the Central Sierra as well as the Northern Sierra. However that may take until next week sometime. In the meanwhile, splitting systems will turn it colder than normal beginning Thursday and on into next week.

Longer Range:

Just a Heads up….

The GFS week 2, the last three runs has been touting a significant split in the energy of the polar jet,  ahead of another blocking high forming in the Central Pacific toward Christmas.. There is “a suggestion” of possibly another AR event, similar to the one that brought so much rain to Northern Ca about a week to 10 days ago. Given that it is later in the season, I would suspect that the upper low will be colder than the last one that developed in the Gulf. Or, the southern stream may be stronger. The effects for Ca depend upon whether the block is more Meridel…. or will it morph into a blocking high that cuts off over AK?..with the resulting river “AR” headed into the Pacific Northwest. In that this pattern has already set up once for the west coast this fall, it is possible that it may repeat in one form or another. Additionally, in that the AO is negative; waters are slightly above normal along the west coast and that the PDO is slightly positive; and that ENSO is slightly warmer then normal; all these indicators give AR events a “slightly higher” bias from an air-sea coupling point of view.

The point is, that although this is “not” a forecast of another “AR” event for the west coast…..it is certainly worth watching to see how the models develop this new weather type over the next two weeks…….

 

Dr Howard and the Dweebs……………………….:-)

 

A Series of Moderate Snow producing weather systems will move through mainly Central and Southern California…..Cooler Weather with lower freezing levels expected….

Monday Am Update….Wednesday’s storm is a Moderate Class Storm:  <6 to 18 inches…..

The Eastern pacific ridge continues its retrogression this week allowing several short waves to effect the central and southern west coast. Although these are not heavy precipitation producers, they will bring moderate amounts of snowfall to our region.

Highlights of System’s Nature:

The models still do not have a good amount of agreement in the fine details of this 1st system.

I Just saw the new 12z Monday GFS.

I like the position of the exit region better now for the Mammoth area. Although it moves through pretty quickly over a 12 hour period, their is quite a bit of UVM “now” crossing our area Wednesday night into Thursday AM. This should make for heavy snowfall for several hours now. There will be plenty of wrap around snow showers Thursday and it will be chilly…..With highs in the 20s Thursday now. Additionally, the GFS really slows the upper low down and lingers it over the SJ valley pretty much for 24 hours between Thursday 4 AM though Friday 4AM, then accelerates it east Friday AM. The next upstream system for the end of the week, is being handled a lot different now. It remains off shore and does not come into Ca at all. I am not buying into the actions of the end of the week system yet as according to the new GFS…it is a no show….

The 12Z Monday NAM:

1. Long wave axis is over the top of California which will tend to slow the systems down as they come into the state..

2. The upper Jet is moderate in strength and initially, does not come inland across the Sierra. As the system digs southeast…it slows and forms a closed low just west of the Bay Area about Wed Noon. There after….the upper jet rounds the base of the newly formed upper low with the front exit region providing most of the UVM over the Northern portions of the Southern Sierra, while Mono County remains in the deformation zone/axis.

The bulk fo the upward vertical motion remains just to the south of Mono County while at the same time the bulk of the 700mb RH moisture is over Mono County. The closed upper low tracks ESE from the Bay Area with a period of up-slope possible later Wednesday night/Thursday AM.   The upper jet rounds the base of a forming closed center effecting South Central Ca. and favoring the central and southern SJ valley and the especially the west side of the Sierra….

2. The system slows as it approaches the coast and closes off.  Good for wrap around for Mono County.  This Model suggests a storm in the 6 to 12 inches range.

I need to see the ECMWF this afternoon….

Note; these snow compact weather systems tend to concentrate the heaviest precip over a smaller area.  Nevertheless…the bulk of the precipitation will be with the southern and central sierra this time with quality snowfall…

Comment……the storm total for the Wed/Thursday system may reach the upper limits of moderate……12 to 18 inches if the GFS is correct…..will fine tune in the morning or sooner if the opportunity presents its self….

 

Dr Howard and the Dweebs…………………..:-)

 

 

Slow Retrogression of the Eastern Pacific High to begin this weekend with the first of the inside sliders to effect the high country in the form of cooler breezy weather Sunday….

 

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Over the next two weeks, a pattern of slow retrogression of the eastern pacific high will take place allowing short wave Trofs to begin their march into the CONUS from the Pacific Northwest about Midnight tonight. The 140 knot upper jet slices diagonally through the state of Washington as it become more north/south orientated with time eventually pointing its energy over northern NV as a 160knot jet. This initiates significant cooling over the Great Basin some of which backs up over the eastern sierra giving us from 5 to 7 degrees of cooling from today’s predicted high of 51. A continuation of slow retrogression builds the eastern pacific high from about 135 to 140 west to 145 to 150west but is not as amplified by Wednesday the 13th/14th.

So the 1st short wave “of interest” may bring a little snow to the high country about Tuesday night/Wednesday. The ECMWF has about .25 of an inch over the crest. So a few inches of snow is possible at this time.  Its trajectory looks too much over land and the position of its upper jet is not as favorable for our area. Another little shot of snow rolls though about Friday night the 14th. It as well does not have a favorable upper jet trajectory for our area.

At this time it is the Sunday of the 16th that begins a series of short waves (Storms), with improving over water trajectory for the Sierra. The Sunday/Monday system may dump a foot or better for our high country. Further retrogression will set the stage for even better snow producing storms about the 18th/19th.

As we move past the Winter Solstice and toward the end of the year….the inter-seasonal models are indicating above normal precipitation. Based upon the long range 500HPA height field from the CPC, some of these storms could be Major Snow producers especially between Christmas and New Years…..

The forecast for this weekend and through Monday is for fair weather through Saturday with breezy conditions developing Sunday in town. Stronger winds northerly winds are expected Sunday “over the crest” 60MPH. It will be sensibly cooler Sunday.

 

Next update Monday…………….

 

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