Wednesday November 17, 2010
Posted at 9:05 am by Howard
Just a quick update this morning…
No real changes accept to slow the progress of main trofs exit early next week into Tuesday. The models have been very persistent in the early timing. So…here we go…..
Expect sunny skies today with light winds. Highs in the mid 50s with winds on the increase this evening becoming moderate by midnight…then gusts to 50 mph Thursday through Friday. There will not be much temperature change until the 1st front moves in later Friday. By Friday, highs will cool to the 40s in town.
Snowfall will occur at about the 6500 foot level Friday night and by Saturday morning there will be about 2 to 3 inches in town and about 3 to 6 inches over the upper elevations. Snowfall will become heavier Saturday and into that night with Blizzard conditions possible along the highway 395 corridor. Travel maybe treacherous along the highway 395 corridor north to Reno. Snowfall should taper off early Sunday. However, snowfall is likely all weekend, and on and off into Tuesday next week. Snowfall ratios will begin at about 10:1 then increase to near 20:1 by the time the Arctic air gets into the region later Saturday. As far as the 550-1000mb Thickness….The magic 540Dm thickness isohyet is located just south of Mammoth by 00z Sunday with further thickness falls down to 528Dm by 12z Monday. Tallies could be some 2 to 3 feet over the upper elevations by Monday morning with a foot or two near the village. Before the main upper trof exits, a cold Arctic born inside slider will put the icing on the cake Tuesday. Milder weather will develop toward Thanksgiving day with an even milder weekend! Another storm looks possible the first week of December………………….
Dr Howard and the Dweebs…………………………………:-)
Reference Glossary of Weather Terms
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.