Current 500ht maps today have 597dm upper high about 138w-39n with upper flow mostly out of the north over Mammoth this afternoon.  By Monday night…ridging upstream near the dateline flattens the upper high with the upper flow pretty much zonal across 50 N. Although changes will occur out over the pacific the next few days….little sensible weather changes are expected here in the Mammoth area through at least Wednesday. Daytime highs will be very pleasant and in the mid 50s with 20s at night.

Global models agree that “strong upstream negative tilt blocking” will be taking place mid-week over the Aleutians. The models are indicating a rapidly intensifying system in the Gulf of Ak with Surface features at 500-1000mb that include a thickness pool of 516dm; Surface high of 1055mb over AK, and a strengthening upper center in the Eastern Gulf of AK of 520dm at 500ht Wednesday am.  Thus by Wednesday morning,  there is a very strong tap of cold arctic air being pulled down from Alaska.  The strong blocking pattern near the Gulf of AK is still negative tilt even through Thursday night as a deep trof and closed low develops near the coast of British Columbia. This long period of negative tilt will allow plenty of Arctic air into the system. Additionally….Model consensus is now quite good compared to a few days ago, so the Dweebs are now on board with the first major storm of the season.  It appears that snowfall may begin as early as Friday morning……however a lot of the moisture with this system will remain off shore until a secondary short wave reloads the upper trof later Sunday.  So the main thrust “is currently” expected into the Sierra , Sunday night and Monday a week a way.

The good news is that if these models are correct….and that is a big if beyond next weekend, the longest range looks dry for the Thanksgiving holiday, with the next large trof rolling in the end of the holiday weekend. (Wishful thinking?).


Just a quick note that that Dweebs believe that this will now be a wet La Nina winter for the Sierra. 100% to 120% of normal. It is mid November and so far the biggest observations to me are that:

1. The Upper jet across the pacific has been much stronger then normal. This will have the effect of limiting blocking patterns. So far there has been insignificant blocking over the western and central Atlantic.

2. This La Nina is associated with one of the strongest negative phase PDOs since the 1950s. This is highlighted by a lot of anomalously cold water over the far eastern pacific. This tends to perpetrate west coast troughing and should lead to wetter than normal conditions, extending well south into the central sierra this winter. Temperatures will average below normal through early 2011. As a note, the odds still favor a drier then normal winter for Southern Ca.

Having a negative phase PDO strongly correlates to having more persistent  troughing in the Jet stream over/or along the West Coast…..and this supports an active, stormy pattern for the West coast and above normal temps over most of the Central and Eastern US. 

Many of the Arctic out-breaks will be displaced west of the Continental divide early this winter and although it will get plenty cold over the northern tier states…cold air penetration will not be nearly as far south as it was last winter. That is because the pattern will be quite progressive as a result of the strong pacific upper jet.

The Dweeber………………..:-)