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Area forecast discussion 
National Weather Service Sacramento California 
955 PM PDT sun Mar 21 2010 


Discussion... 
as the upper trough moved into Oregon at press time...much of the 
synoptic scale moisture had been shunted east and S of interior 
norcal. There are exceptions...a strato-cumulus deck along the 
80/50 corridor in the Sierra Nevada in which BUFKIT forecast soundings 
suggest this moisture will linger over the area through Monday afternoon. 
Developing northwesterly winds on Monday will likely erode the cloud cover 
during the day. Also...strato-cumulus is developing over portions of 
Shasta Colorado...and these clouds should also linger into Monday and may not 
get mixed out until after short wave passage and developing northwesterly 
winds Monday afternoon. 


A secondary wave vicinity of 45n/135w is forecast to move across norcal 
on Monday. Winds will turn northwesterly behind the short wave and subsidence 
will increase which should erode any remaining cloud cover. It does 
not look as if the short wave is strong enough to result in breezy 
conditions...just a noticeable northwesterly wind 10 to 20 miles per hour with possible 
gusts up to 25 miles per hour over the northern half of the SAC valley. 850-700 mbs 
temperature advection forecast indicates these will be cold air advection northerly winds...but the 
downslope adiabatic warming effects will partially offset the cold air advection. 
Maximum temperatures should be warmer of the northern SAC valley due primarily to more 
solar insolation/less cloud cover than today...while slight cooling 
is expected elsewhere. Jhm 




Previous discussion... 
Monday night into Tuesday...upper ridge builds into the area for 
warming temperatures and dry weather. 


Next chance of moisture looks to currently be Wednesday night as 
models coming into fair agreement that a trough with some negative 
tilt will push into the area. This system is pretty progressive and 
if it continues with current model trends would push an area of 
moisture across the area Wednesday night into Thursday morning 
quickly. Latest European model (ecmwf) has trended a bit slower with the system so 
timing still a bit uncertain. Rasch 


Extended discussion (thursday through sunday)... 
medium range models showing diverging solutions through the extended 
period. Systems prognosticated to move through persistent strong ridge 
Thursday and Friday but models differ significantly on depth/timing/ 
and track. Models in general agreement for shortwave ridging 
following Saturday. Warm front then extends into interior norcal 
Sunday. Will continue low precipitation probabilities for these 
periods...over the northern half of the County Warning Area and mainly over the 
mountains. 


&& 


Aviation... 
VFR conditions generally expected the next 24 hours as a cold front 
exits the region. A few light showers may continue over the higher 
elevations of the northern Sierra through 09z. Through the 
valley...light onshore winds will become northwesterly 10-20 knots with 
local gusts to 30 knots during the day Monday. 


&& 


Sto watches/warnings/advisories...none. 


&& 


$$