018 
fxus65 kpsr 192216 cca 
afdpsr 


Area forecast discussion..correction 
National Weather Service Phoenix Arizona 
315 PM MST Wednesday Nov 19 2008 


Synopsis... 
high pressure aloft will continue to weaken tonight and Thursday 
under mostly clear skies. By Friday and Saturday...some high level 
clouds will drift into the area...but temperatures should remain 
above the seasonal normals. By the middle of next week...a major 
change in the pattern will lead to cooler weather...and a slight 
chance for showers to the east of Phoenix. 


&& 


Discussion... 
upper level ridge and strong subsidence continues across the area. 
With full sunshine...temperatures have already jumped into the 
middle 80s at Sky Harbor Airport...along with very dry relative humidity 
values...into the single digits across some desert cities. Look for 
minimum temperatures to drop off quickly again tonight with this dry air. 
Temperatures today will push close to the daily records...and only a 
slight drop off in maximum temperatures expected over the next couple days. 
Heights and thicknesses prognosticated to remain above normal into this 
weekend...even as a split flow in the westerlies shapes up just 
offshore from southern calif. Models pretty similar in advertising 
variable amounts of clouds above 15 thousand feet...while the lower 
levels stay on the dry side. Except for a weak back door frontal 
system that will produce a little stronger breeze in our eastern 
zones early Friday...no strong winds expected. 


As we have been talking about...the big changes in the pattern may 
come about next week...with both European model (ecmwf) and GFS now carving out a 
major trough near the West Coast on Wednesday. This will be a cold core 
low that could result in considerable large scale forcing and 
thicker cloud coverage...and possibly some showers. Best chances for 
showers on Tuesday still appear to be over the higher terrain of 
zone 24. 


&& 


Aviation... 
high pressure aloft combined with a dry airmass will keep skies 
clear and winds light through at least 18z Thursday. No aviation 
concerns anticipated. 


Aviation discussion not updated for amended tafs. 


&& 


Fire weather... 
temperatures will begin to cool as the high pressure...that has been 
dominating of late...begins to weaken by the end of the week. As 
this occurs...high clouds should spread over the area at times while 
winds remain light and minimum relative humidity values reach the middle teens by 
early next week. 


&& 


Psr watches/warnings/advisories... 


Arizona...none. 


California...none. 


&& 


$$ 


National Weather Service Phoenix is on the internet at 


Weather.Gov/Phoenix 


Discussion...Sipple 
aviation...Rogers 
fire weather...paddock