274 
fxus66 kmfr 202153 
afdmfr 


Area forecast discussion 
National Weather Service Medford or 
253 PM PDT Sat Mar 20 2010 


Discussion...an upper low near 48 north and 135 west will allow 
a trough and associated cold front to move toward the coast this 
evening. This will bring cloud cover and the chance of rain to the 
coast tonight. NAM and GFS indicate the front will stall just 
inland overnight but will get a significant push inland tomorrow 
as a stronger shortwave moves into Oregon. This will bring a 
period of rain to most areas from the Cascades westward with 
amounts generally 0.10 to 0.25 of an inch with local amounts up to 
0.50 of an inch in a few favored areas of western Siskiyou 
County and the South Coast zones. Rain will also reach the east 
side as the front moves eastward tomorrow...but much of the 
precipitation will fall apart. With the exception of the higher 
terrain...amounts there should be less than 0.10 of an inch. It 
will be noticeably cooler tomorrow...around 10 to 15 degrees lower 
than today for highs. 


Post frontal showers will continue tomorrow night and into Monday 
as one last shortwave moves through on the back side of the 
trough. Highs Monday will be within a couple of degrees of normal. 
But an upper level ridge will build into the area Monday night 
into Tuesday providing a warming trend with offshore flow and a 
thermal trough setting up along the coast. Temperatures Tuesday 
will rebound back into the upper 60s over the west side valleys. A 
strong temperature inversion will set up Tuesday night keeping the 
ridges warmer than the valleys and made some adjustments to min 
temperatures to reflect this. Mas 


Wednesday morning Onward...after the upper ridge moves eastward 
Wednesday...European model (ecmwf) and GFS ensembles in very good agreement with front 
cycling through the region Wednesday night. From Thursday Onward 
the plots diverge with generally a noisy progressive zonal flow 
pattern emerging in the ensembles. Long range timing of systems 
in this pattern is an exercise in self delusion and have broad 
brushed probability of precipitation through the remainder of the extended. Sven 




&& 


Aviation...VFR nearly all areas late this afternoon and early 
this evening...except MVFR ceilings and light rain developing at the 
coast as the front pushes eastward. MVFR ceilings with local mountain 
obscurations spreading inland tonight over west side areas and 
continuing into tomorrow with a period of rain. VFR tonight over 
the east side with MVFR ceilings and local mountain obscurations 
developing tomorrow along with a period of rain. 




&& 


Mfr watches/warnings/advisories... 
or...none. 


California...none. 


Pacific coastal waters...none. 


$$ 


Spilde