091 
fxus65 kpsr 232346 
afdpsr 


Area forecast discussion 
National Weather Service Phoenix Arizona 
445 PM MST Wednesday Jul 23 2008 


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


Update...updated aviation section. 


&& 


Synopsis... 
weak monsoonal flow will continue over Southeast Arizona through 
Friday. Diurnal afternoon and early evening showers will therefore 
continue on Thursday and Friday. Drier air that has worked its way 
into the region...will keep most activity on the higher terrain 
north and east of the Phoenix metropolitan area. A change in weather 
might be lurking around the corner though...as the remnants of 
Hurricane Dolly ejects a significant amount of moisture from the 
east back into the lower deserts this weekend. 


&& 


Discussion... 
the drier air noted on this mornings psr sounding...was a good 
indicator that the airmass had modified over Southeast Arizona. The 
drier air at the surface was also noticeable in surface 
observations...with drops in dewpoint temperatures of 15 to 20 
degrees being reported at many locations across the region. Showers 
and thunderstorms that developed early this morning over southern 
Gila County tracked slowly to the southwest during the morning 
hours...but gradually diminished as they moved into the more stable 
environment. The European model (ecmwf) and GFS both show the 500 mb upper level ridge 
access located over the Central Plains...though an axis of high 
pressure is oriented from The Four Corners region to the southwest 
across central Arizona. The ridge is forecast to flatten over the 
next 24-hours...but generally remain fixed in its current 
position...as a couple of shortwaves creep up its backside. Little 
change in this pattern is expected through Friday...so will be going 
with a somewhat persistent forecast. This will mean high 
temperatures varying little from readings of today and a 
continuation of a low grade monsoon. Showers and thunderstorms that 
do develop during this period are expected to be confined mainly to 
the higher terrain east and west of Phoenix. 


This weekends forecast will be more of a challenge however...as the 
moisture associated with the remnants of Hurricane Dolly work their 
way toward the northwest. Big differences between the European model (ecmwf) and GFS 
on the trajectory and amount of moisture working its way into our 
forecast area...with the European model (ecmwf) more northwest and less quantitative precipitation forecast than the 
GFS. The 12 UTC European model (ecmwf) is trending more toward the GFS and has backed 
off from the 2.75 inch bullseye of precipitation that was forecast in the 
00 UTC run. Regardless of the solution accepted...the weekend looks 
like it will see the monsoon increase in intensity...with a higher 
occurrence of showers and thunderstorms. Our earlier forecast 
package already showed a ramp up in probability of precipitation...so kept this trend going. 


Beyond the weekend...it is really anyone's guess. At this point in 
time...there doesn't appear to be anything upstream to wipe out our 
moisture...so we'll continue a low grade monsoon forecast though the 
extended...with showers/thunderstorms favoring the higher terrain 
and temperatures running a couple degree below average for late July. 


&& 


Aviation... 
south-central Arizona...kphx/kiwa and surrounding airfields... 
although steering flows are beginning to become more favorable for 
the region...the atmoshpere has dried out to the point that thunderstorm 
threat is minimal. Could see an outflow approach the region from the 
NE from activity along and S of the Mogollon Rim...but even this 
remains only a remote possibility at this time. Therefore...kphx/kiwa tafs 
will be highlighted by no convection and only some minor debris middle 
and upper level cloudiness tonight into Thursday morning. Expect 
normal surface wind behavior...with speeds generally less than 10kts. 


Southwest Arizona and southeast California...kyum/kblh and kipl... 
airmass much drier and more stable with no threat of thunderstorms 
through 00z Friday. Expect light winds favoring the south throughout 
the day...light and variable overnight. 


Aviation discussion not updated for amended tafs. 


&& 


Fire weather... 
no significant fire weather concerns Friday though the weekend...and 
into early next week. Airmass will be gradually wetting up Friday 
through Sunday as moisture from Hurricane Dolly works westward and 
into the state...leading to a chance for showers/thunderstorms 
across south-central Arizona by Saturday...with possibly a better chance 
Sunday. As humidities rise...maximum temperatures will lower...likely to well 
below normal values by Sunday. With no significant mechanism to 
really dry things out next week...we will keep at least a Standard 
grade monsoon forecast going...with maximum temperatures to climb to near 
normal by the end of the period. 


&& 


Psr watches/warnings/advisories... 


Arizona...none. 


California...none. 


&& 


$$ 


National Weather Service Phoenix is on the internet at 
weather.Gov/Phoenix 


Discussion...McLane/wanek 
aviation...estle 
fire weather...cumulonimbus