Tuesday November 16, 2010
Posted at 9:16 am by Howard
A Rex Block has already established itself near the dateline with a negative tilt upper ridge transporting cold Arctic air via the Bering Sea into the Gulf of Alaska. The lead short wave is now in the Gulf of Alaska sporting an Ht 500, 528dm upper center. Over the next 24 hours… more Arctic air wrapping into the upper low will push the upper center south to near 55N/145W, while our off shore ridge at 140w becomes ever so squashed. During the next few days, a rather large 500-1000mb thickness pool of 516dm covers much 0f the Gulf of Ak and is diffluent into the surface low spinning up off the BC coast Wednesday morning. Temperatures at 700mb over Alaska are between -20c & -25c. Pretty cold for Mid November. The 500MB Height Anomaly showed a center, greater then -36 Deca-Meters off the Oregon coast Saturday night. This is one deep upper low for Mid November. These heights would be more common later in December. No wonder the upper jet is so strong and why it will be a particularly windy storm with the potential for Blizzard conditions later in the weekend along the 395 corridor and here locally in town.
Preliminary QPF from HPC is 1.3 inches over the crest by Saturday night. However, it is way too early to speculate on snowfall amounts until we get closer to Friday. All the Dweebs will says is that there is “the potential” for several feet of snow over the upper elevations. As a note, there is not any subtropical tap shown now, like was indicated some 5 days ago. Nevertheless, with an upper jet this strong, and an unusual amount of cold air aloft and good over water trajectory, this system will generate plenty of its own moisture!
Long Range Week 2:
The Dweebs are still expecting a break for the traveliers of the Thanksgiving Holiday. The 8 to 14 days outlooks show normal precip beginning the 23rd through the 29th. The weather for Thanksgiving at the moment shows upper ridging and thus fair weather.
Dr Howard and the Dweebs………………………………:-)
Reference Weather Glossary
Mammoth to enjoy highs in the 50s the next 5 days, before 1st major storm makes its way into the sierra Friday
Sunday November 14, 2010
Posted at 8:46 am by Howard
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.
Fair Dry Weather Expected Through Wednesday With Warmer Temps…..Gusty Winds Over The Crest Will Continue…..Storm Still Lurking For Next Weekend
Saturday November 13, 2010
Posted at 8:57 am by Howard
Upper ridge at 140west….and mean trof over the central Conus with the upper jet north/south in-between. That’s the dry story through mid week. Outside of strong gusty winds at times over the crest and high clouds on Sunday….not much going on. Expect highs in the low 50s in Mammoth and lows in the 20s. Beautiful Fall Weather!
Medium Range models now beginning to look simular. (GFS-ECMWF) There are timing issues between them. The Global Forecast system has been leading the way with the big weather change and now the EC is following suit.
Both global models initially retrograde the big upper high near 140w midweek. Both models develop a strong upper jet that taps into a vary cold air-mass, then phases it with southern stream energy with plenty of moisture.
Last nights 00z GFS had strong amplification early Tuesday morning near the dateline which taps a very cold air-mass over Alaska while southern stream energy undercuts the strong mid latitude upper ridge that is building northward. Cold arctic air is pulled south from about 80 degrees north between the strong upper high over the Aleutians and the cold upper low developing in the Gulf of AK near 140W.
By Wednesday morning…..the present upper ridge is flattened with the dominant upper ridge back at 170w. This retrogression in the long wave features actually coincides with progression in the long wave features next week. Since there is no blocking down stream at the moment, slow progression should continue into the weekend.
The screeming question is…. Will the cold upper trof tap southern stream energy. Or….will there be southern stream energy to tap into? Allot will depend upon “how far north the upper high builds into the Gulf of AK” If the upper anti cyclone doesn’t get north enough into the gulf, southern stream energy probably won’t be much of a factor and we’ll just have a nice cold storm to deal with.
Strong Blocking is really beginning to show it ugly head over Greenland by the the end of the month. The Dweebs have been waiting for it. The QBO has been growing more and more positive and thus stratospheric winds blowing west to east at the Equator are strengthening. This is pretty common for La Nina Winters. The block and Negative NAO phase has the effect of really deepening the Hudson Bay Low and slowing the progression of storms into the west coast. Lets hope we get a bonanza of precipitation next weekend!
Stay Tuned……The Dweebs have you covered…………………………..:-)