Weather

685 
fxus65 kpsr 212206 
afdpsr 


Area forecast discussion 
National Weather Service Phoenix Arizona 
305 PM MST Thursday Aug 21 2008 


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




Synopsis... 
high pressure aloft will build over the southwest United States the 
next few days. This system will tend to suppress the formation 
of thunderstorms across the area throughout the weekend...and it 
will also be responsible for giving hotter temperatures. Look for a 
gradual lowering of afternoon temperatures the first half of next 
week...along with the return of a slight chance of thunderstorms to 
the higher terrain locations east of the greater Phoenix area. 


&& 


Discussion... 
stable conditions are evident on the satellite and radar data with 
no storms in Arizona or southeast California as of this writing. 
Both NAM and GFS continue to show the anticyclone currently centered 
off the northern Baja California coast migrating to the vicinity of the 4 
corners by Saturday afternoon. They also indicate a small intrusion 
of moisture developing over our forecast area Friday...not quite in 
the same places but not focused over higher terrain either. The NAM 
pushes the moisture southward Saturday while the GFS pushes it 
further west. NAM begins to increase moisture from the east Sunday 
as an inverted trough passes to the south. The GFS keeps the 
inverted trough stalled out over northeast Mexico/southwest Texas 
and depicts less moisture. 


It remains to be seen how the moisture fields will change. As the 
main anticyclone position changes...an eventual return of deeper 
moisture is reasonable but stability will still need to be overcome. 
Will keep previous forecast trends going with only probability of precipitation being over 
zone 24 beginning Sunday. 


For temperatures...a slight increase is expected as the anticyclone 
center gets closer. If GFS 925 and 850 mb temperature trends are taken at 
face value...many desert locations could exceed 110 this weekend. 
However...MOS guidance is not quite that hot. Gradual cooling trend 
next week still looks good as operational GFS...GFS ensemble 
mean...and even European model (ecmwf) are depicting a weakening high as a trough 
passes to the north. 


&& 


Aviation... 
south-central Arizona...kphx/kiwa and surrounding airfields...and 
southwest Arizona and southeast California...knyl/kblh and kipl... 


Dry west to northwest flow aloft will allow for clear or mostly 
clear skies across the area through at least 18z Friday. Surface/middle 
level gradients are rather weak...thus mostly light diurnal surface 
winds will occur this afternooon through Friday afternoon. Winds out 
west...along lower Colorado River valley...will favor the south. Afternoon 
and evening winds over the central deserts...from about 21z through 
04z...will favor the southwest to west at less than 15 miles per hour. 


Aviation discussion not updated for amended tafs. 


&& 


Fire weather... 
Sunday through Thursday... 
overall hot and rather dry conditions are expected Sunday into the 
middle of the week. High temperatures will approach or exceed 110 
over the hotter deserts Sunday and Monday...then trend downward 
slightly each day. Moisture will be limited...but sufficient for 
isolated afternoon and evening thunderstorms over the higher terrain 
east of Phoenix each day. It is possible that some moisture may 
spread westward the lower deserts early next week. Generally light 
winds...gusty at times with peak heating of the day...and weak 
drainage flows at night...are anticipated. 


&& 


Psr watches/warnings/advisories... 


Arizona...none. 


California...none. 


&& 


$$ 


National Weather Service Phoenix is on the internet at 


Weather.Gov/Phoenix 


Discussion...aj 
aviation...cumulonimbus 
fire weather...cumulonimbus