Area forecast discussion 
National Weather Service Phoenix Arizona 
118 PM MST Wednesday Aug 27 2014 


Synopsis... 
drier air will continue to move into the region tonight...ushering 
in a drier and warmer pattern across the Desert Southwest through at 
least early next week. High temperatures will return to near normal 
values by Thursday...peaking between 105 and 110 Friday and 
Saturday...before retreating slightly next week. 


&& 


Discussion... 
early afternoon water vapor imagery continues to reveal an upper low 
over Utah with a very weak shortwave trough moving through eastern 
Arizona. Radar and satellite imagery indicate that a few cumulus and even 
a few showers have developed in the higher terrain locations east of 
Phoenix...but skies were clear to the west of Maricopa County. Temperatures 
as of 20z were generally in the upper 90s across the lower deserts 
although there remained quite a dewpoint discontinuity from Yuma 
/dewpoints in the low 40s/ to Phoenix /dewpoints in the lower 60s/. 


Dry advection in the low levels and warm advection aloft will 
continue across the area this evening which will significantly limit 
the amount of convection across the area. The highest likelihood of 
showers remains in the mountains east of Phoenix...but these chances 
will diminish quickly with the loss of daytime heating after 02z. I 
will maintain 10-20 probability of precipitation east of Phoenix through early evening with 
zero probability of precipitation overnight as strong subsidence takes hold. 


The forecast for Thursday through the weekend remains largely 
unchanged...dry weather with increasing temperatures. Probability of precipitation were 
already zeroed out during this period and with warm 500 mb temperatures 
around -3c...bl mixing ratios around 4-5 g/kg and no MLCAPE to speak 
of...will be difficult to get any cumulus let alone storms. 
Consequently...temperatures will be on the rise eventually maxing 
out between 105-110 across the warmest desert locations. 


The upper ridge will begin to break down on Saturday as a trough 
moves into the Pacific northwest. Models are in excellent agreement 
this trough will flatten the ridge to our southwest...but keep US 
under a westerly to northwesterly dry upper level flow into next 
Monday. Highs should start to trend downward starting Sunday as the 
trough to our north slowly knocks down our upper heights. Some model 
differences are shown near the end of the forecast period for next 
Tuesday and Wednesday as the European begins to rebuild the 
subtropical high to our southeast and possibly allows for some 
minimal moisture return under weak southeasterly flow. The GFS keeps 
the drier westerly flow aloft under a weaker sub-tropical high 
centered still to our southwest. To account for the potential return 
in monsoonal moisture...have introduced at least some low end slight 
chance probability of precipitation for Tuesday and Wednesday across the higher terrain in 
Gila County. 


&& 


Aviation... 
south-central Arizona including kphx...kiwa...and ksdl...and 
southwest Arizona and southeast California including kipl and kblh... 


Strong subsidence behind a departing trough will take hold across 
the area tonight. As a result...weather concerns are minimal through 
Thursday. Mostly clear skies and light diurnal winds are forecast at 
all sites. 


Aviation discussion not updated for amended tafs. 


&& 


Fire weather... 
Saturday through Wednesday... 
northwest flow and dry conditions will prevail across the area 
through early next week...with no storm chances expected across the 
region. Moisture will return to far eastern Arizona by the middle of 
next week but until then...there will be a break in the typical 
monsoon pattern. Afternoon humidities will drop into the teens each 
day with fair overnight recovery expected. Recoveries will slowly 
improve as moisture increases next week. Winds will be light through 
next week with no major wind events expected. 


&& 


Psr watches/warnings/advisories... 


Arizona...none. 


California...none. 


&& 


$$ 


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Discussion...leins/Kuhlman 
aviation...leins 
fire weather...leins 



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