Spliting Trof to Bring Light Snowfall Today and Tonight…..Then another weakening system is expected later in the weekend…..Stronger, Better Snow producing Weather Systems are expected to begin about the middle of Next Week………
Wednesday December 12, 2012
Posted at 9:57 am by Howard
The ECMWF is in……
The Saturday Sunday storm is a dud…..
Not much has changed from yesterdays thinking as the current trof is well into splitting SSEastward. A weakening cold front will bring the possibility of a few inches of snow today, however, it is expected to stall over southern Mono County tonight with additional snowfall a possibility. This stalling is a Maverick to the current forecast and may produce more snowfall over night than expected.
As the upper trof splits and slows today, it spins up a rather amorphous closed upper level low both at 500mb and 700mb near the Bay Area, then drops south during Thursday to near Bakersfield. This will create both divergence aloft in its NE quad and up-slope flow to the north along its axis. Precipitation in the form of snowfall could be heavy in parts of Western NV like Tonopah; However, the Sierra from Tahoe south will benefit from the up-slope later Thursday as well as Mammoth by Thursday night as it pushes east along 35N into Nevada. Overall, the pattern and its UVM Favors Arizona as well as New Mexico. Snowfall amounts should be in the 2 to 5 inches range by morning Thursday or a bit more if the stalled front remains active. Additionally, there may be a bit more snowfall accumulation with upslope Thursday night.
This is a very complicated pattern that the models are dealing with. They are still out to lunch on the late weekend system. The new 12z GFS is non existent for the system late Saturday into Sunday. The Dweebs will take another look at the EC this afternoon to see if the model is consistent with earlier runs. However, unless it is…the feeling now is that there is only a slight chance of showers now from that Saturday night Sunday system.
So…..there is a weakness in the mean heights over California. However, the long wave is still having issues with wave length which is causing a split off shore…probably due to the REX block down stream over Greenland and South. I believe that this has forced a positive height anomaly over the Mid Atlantic states with the upstream effect a split off the Ca. Coast. The good news is that this mess will be progressing out of our region early next week as the wave length relaxes. This means in this case, there will be a higher degree of forecast visibility for the longer term once we get past this weekend.
What the 500mb GFS means are showing is that the REX Block south of Greenland is forecasted to break down beginning this Sunday with the upstream wave length stretching out across the US next week. At the same time, across the pacific, amplification occurs with the Central Pacific 500mb High building northward at about 170W mid week. The results for the Ca. West Coast is that the upper flow gradually Consolidates next week. Thus we get rid of the current pattern to one which should be much more dynamic for the Sierra. By Monday, the Dweebs feel that much better visibility and agreement will be in both EC and GFS global models. Better timing as well is possible, as larger snow producing storms will be able to move onshore as we near the solstice.
PS the Idea of a strong southern branch of the jet stream hitting California is still in the cards for later in the month!!!!
Next update for the late weekend system later today or in the AM.
Dr Howard and the Dweebs………………………….:-)