Upper Low To Track More East Now So Not As Much Cooling Expected For The First Few Days of Fall…..Instability still in the cards for the weekend and into next week….
Friday September 21, 2012
Posted at 8:54 am by Howard
Friday AM Update: 9:45am
9:35am update for 12z GFS… GFS has upper low and main cooling holding off as well until Sunday into Monday. It also dives briefly the system SE into NW Nevada Sunday afternoon, clipping NE California. So the GFS is a bit cooler then the NAM and should be favored for consistency. The upshot is that sensibly, is still looks like; 1. Cooling to be really delayed until the end of the weekend…and into Monday. 2. Not as much cooling as earlier expected.
Friday AM update:
The recent trend overnight, as well as in this mornings 12z runs are back peddling now on the amount of cooling expected over the weekend. Last night 06z gfs, as well as recent runs of the new 12z WRF (NAM), has the small upper low tracking mostly east now….north of the California border instead of SSE through Northern Ca. This will at least delay most of the cooling until Sunday/Monday. Additionally, some cooling “aloft” today will allow instability to develop for a few showers or isolated TSRW over the Sierra (Last of the Summer Convection) (Fall arrives Saturday AM at 7:49PDT).
What appears to be happening is that this weak system to the north is going to change the configuration of the subtropical high off-shore at 700mb, allowing moisture and instability IE(UVM) to be channeled up from the south into the Sierra Sunday. So there is a bit better chance of some showers and or TSRWs Sunday and NGT, but not directly from the upper low itself. By Monday, we will experience the effects from the back side of the upper low and so NNW flow should bring in “Cool Air Advection” and stabilize the air mass over the Sierra. (Less chance of showers). The cooling should bottom out Monday with highs in the mid 60s. The Dweebs are expecting little change in temps Tuesday, then a bit of a warm up Wednesday into Thursday. Possibly 70+ again. Another shot of showers may arrive from the south by Thursday pm into Friday. (Subtropical Moisture).
All in all, the weather is changing over the CONUS and all signs are pointing to change associated with Fall and the strengthening of the westerlies and the weakening of the Summertime subtropical high. We’ll all shed a tear today as summer retires to Fall………This was Mammoth’s Best Summer Ever!!!!!
Dr Howard and the Dweebs………………………….:-)
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