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CNRFC Hydrometeorological Discussion

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Hydrometeorological Discussion
National Weather Service / California Nevada RFC / Sacramento CA
1015 AM PDT Sat Sep 25 2021

...ISOLATED TO SCATTERED SHOWERS OVER PORTIONS OF SOCAL AND FAR SRN 
NV THIS WEEKEND...
...COOLER TEMPS WITH PRECIP OVER SRN OR AND NRN CA/NV SUNDAY NIGHT 
INTO TUESDAY AND OVER ERN NV INTO WED...

.METEOROLOGICAL CONDITIONS (SAT AM - FRI AM)...

Upper level low off the coast of Baja CA will move east today and 
into Arizona on Sunday. Instability with the low along with some 
moisture will bring showers and thunderstorms to Srn CA (mainly over 
the Mtns from eastern San Gabriel Mtns down to the Laguna Mtns and 
SE Deserts) and far Srn NV this weekend. Forecast uses WPC with a 
mix of some EC true res at times. 

An upper level trough and associated front approach the Pac NW on 
Sunday and  move through the Pac NW and Northern CA on Monday into 
Tuesday bringing precip to Nrn CA and Srn OR. The trough moves into 
Nevada and stretches into Srn CA later Tuesday into Wednesday for 
possible showers over Nevada (especially Eastern portion). PW plume 
about 1.2 inches along NW CA coast Monday morning weakens as it 
moves south around the Bay area late Monday afternoon into Monday 
evening. Precipitation amounts for the Smith River Basin generally 
around 0.66 - 1.25 inch and 0.5- 1 inch for Srn Cascades and 
generally less than a  third of an inch elsewhere in the north with 
precip possibly south to the Russian Basin and into the Central 
Sierra. Forecast mainly used WPC. Freezing levels above 10000 ft 
drop down to around 6000 near the ORCA border and around 8500 ft for 
the Northern Sierra Tuesday morning. 

Another trough may approach the Pac NW and brush by NW CA Thursday 
although models and ensemble mean continue trending weaker and 
farther north.  Operational GFS and EC runs dry for our region but 
some ensemble member still showing brushing our area with the 
ensemble means showing a little bit of precip over NW CA and Srn OR 
(although less precip and farther north in latest runs). Forecast 
used decreased WPC amounts with drier conditions expected on 
Thursday. Looks like the latest WPC is mainly dry Thursday.