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Area forecast discussion 
National Weather Service Sacramento California 
345 am PDT Sat Aug 30 2008 


Discussion... 
tumbling temperatures today and tomorrow as the approaching trough 
delivers a colder airmass over northern California. This should 
translate to maximum temperatures falling about 20 degrees over the next 
two days. Yesterday's triple digit heat will transform into the middle 
90s today and low-middle 80s by Sunday for our valley locations. 


As the base of the trough moves across our County Warning Area on Sunday...GFS, NAM, 
and European model (ecmwf) models show a vorticity maximum affecting northern California. 
Early Monday our County Warning Area will be on the back side of the trough and all 
models suggest another...stronger...vort maximum swinging over the 
Sierra crest. East to west and north to south cross-sections of our 
County Warning Area are not indicating much moisture during the passage of these 
vorticity maxes...plus instability looks to be better on the eastern side 
of the Sierra crest...so have kept forecast dry. Should any 
thunderstorms develop in the northern mountains Sunday night into 
Monday...they should be very isolated. 


The main concern for Sunday and Monday into Tuesday will be gusty 
northerly winds on the back side of the trough. GFS 06z model shows 
a north-south gradient from Medford to Sacramento ranging 9-11 mb 
from Sunday morning through Monday evening...however the pressure 
pattern transforms from a straight northerly gradient on Sunday to a 
more northeasterly gradient on Monday. 925 mb winds over the 
Sacramento Valley are showing 20-30 kts with good upper level 
support at 700 mb peaking around 35 kts. Surface winds in the valley 
could see sustained winds around 20-25 miles per hour with locally stronger 
gusts...wind speeds could be near Wind Advisory criteria if models 
remain consistent. A Fire Weather Watch remains in effect for most 
of the County Warning Area starting Sunday night through Tuesday morning for gusty 
winds and dry conditions. 


Winds will lessen during the day Tuesday as the trough flattens and 
moves well east of our region. High pressure begins to re-establish 
over the eastern Pacific raising 500 mb heights and putting US back 
into a warming trend under a dry airmass. Only change to extended 
forecast was a nudging up of temperatures for Thursday-Saturday 
since both European model (ecmwf) and GFS guidance showed a warm up of 850 mb temperatures 
putting US back into triple digit heat...103-109...for much of the 
valley towards the end of the week. Did not warm maximum temperatures as much 
as the models indicated but did increase valley values 99-101 for 
Friday and Saturday. Jbb 


&& 


Aviation... 
VFR conds today. Winds will be generally light except gusty southwest 
winds over higher mountains this afternoon and evening as the upper 
trough over the epac apprchs the west CST. 


&& 


Sto watches/warnings/advisories... 
Fire Weather Watch for the northern and central Sacramento Valley 
and the adjacent mountains and foothills for Sunday 5 PM EDT through 
Tuesday morning 11 am PDT. 




&& 


$$