Weather

161 
fxus65 kpsr 062147 
afdpsr 


Area forecast discussion 
National Weather Service Phoenix Arizona 
245 PM MST Monday Oct 6 2008 


South-central and southwest Arizona...and southeast California 
forecast discussion 


Synopsis... 
a warming trend will persist through Wednesday as high pressure 
builds back over the region. Temperatures will warm to well above 
seasonal normals by Wednesday afternoon across the lower deserts. A 
strong low pressure system will develop over the western states 
later this week...with cooler temperatures and breezy conditions by 
the weekend. 


&& 


Discussion... 
a warming trend will take place over the next several days as upper 
level ridge strengthens over the Pacific...leaving the forecast area 
in a dry northwesterly flow aloft. Temperatures will peak on 
Wednesday with forecast high temperatures near 100 degrees across 
the lower deserts. Latest mav guidance came in a bit warmer for 
Phoenix...and we will now go with a high of 100 for Wednesday. 
Expecting generally clear skies and light winds through the middle 
of the week. 


After Wednesday...temperatures will begin to trend down again as a 
strong low pressure system develops over the western U.S. The latest 
GFS is more in line with what the European model (ecmwf) has been 
advertising...although there are still some differences in the 
position and intensity of the low. Nonetheless...winds will begin 
increasing Friday...and may become fairly strong Saturday into 
Sunday. In addition...temperatures are expected to be much cooler 
this weekend. Still hard to pinpoint how dramatic the temperature 
change will be as there is a sharp baroclinic gradient associated 
with this trough...so a slight change in position could have a big 
effect on the temperatures. Models are keeping this system 
relatively dry as trajectory remains over land...with any associated 
moisture remaining farther north near the cold core. Thus...will 
only keep single digit probability of precipitation for our area. The low will eventually 
move to the east...leaving the southwest U.S. In dry north to 
northwesterly flow early next week. 


&& 


Aviation... 
high pressure aloft will continue to build across southeast 
California and southern Arizona...leading to clear skies and light mostly 
diurnal winds across all taf sites for the next 24 hours. VFR 
conditions expected at all airfields. No aviation concerns. 


&& 


Fire weather... 
Friday into the weekend... 
a large storm system may develop over the western United States by 
Friday or Saturday. Our area should be on the southern edge of the 
low and under a dry westerly flow aloft. Minimum relative humidity values should 
stay below 15 percent over the deserts each day...with modest relative humidity 
recovery at night. There is a possibility that breezy to windy 
conditions will develop Saturday and into Sunday as a cold front 
sweeps across the area. Gusty north winds may develop behind this 
system...especially in zones 131 and 231. 


&& 


Psr watches/warnings/advisories... 


Arizona...none. 


California...none. 


&& 


$$ 


National Weather Service Phoenix is on the internet at 


Weather.Gov/Phoenix 


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