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fxus65 kpsr 231338 
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Area forecast discussion 
National Weather Service Phoenix Arizona 
630 am MST sun Nov 23 2008 


Update...updated aviation and fire weather discussions. 


Synopsis... 
high pressure aloft will remain strong over the area through Monday 
and will give lots of sunshine and continued warm temperatures. The 
rest of the week will see some rather drastic changes in our weather 
pattern as a series of Pacific low pressure systems begin to move 
into the southwest United States. The first system will likely give 
showers to the region as early as Tuesday evening over the west... 
spreading to the east on Wednesday and continuing into Thanksgiving 
day. Yet another low pressure system will bring a renewed chance of 
showers next weekend. It will also turn seasonably cool by midweek. 


&& 


Discussion... 
a very interesting weather scenario is shaping up for this Thanksgiving 
Holiday week. First off...our current upper high will temporarily 
amplify over the region through Monday...so we can expect continued 
mild temperatures and mostly sunny skies to start the new week off. 


After this...all models are beginning to converge on similar 
solutions regarding upcoming eastern Pacific/western U.S. Troughing. First 
trough will push into the area from the California coastal regions by late 
Tuesday/Wednesday time frame. Good vertical motions expected in advance of 
the low...and a significant plume of subtropical moisture also 
expected to move up ahead of low to feed the dynamics. Latest mex 
MOS trending more into likely precipitation category...and this certainly 
appears reasonable in light of the above. Therefore...have upped 
probability of precipitation for scntrl Arizona portion of County Warning Area Wednesday and Wednesday night...and also 
introduced the mention of thunderstorms as air mass destabilizes. Quantitative precipitation forecast amounts are 
still iffy at this time...but HPC idea of at least one to two inches with 
first trough through Thanksgiving morning in upslope areas of scntrl Arizona 
appears reasonable. And...any strong thunderstorms could locally 
enhance those amounts. It will also obviously turn much cooler what 
with the lowering thicknesses...increased clouds and rain by Wednesday 
and Thanksgiving day. 


The tail end of the week contains more uncertainty regarding the 
forecast. At least a couple more pieces of shortwave energy appear 
poised to affect the regional weather. However...timing and exact 
location of this second shot of rain is still very much in the air. 
For now...will keep Friday as kind of an in-between day...with next 
precipitation event sometime over the Holiday weekend. Will therefore keep 
forecast very broad-brushed for now. However...there are signs from 
the latest GFS that the final upper low may stay off the West Coast 
as a closed low feature...and hold off moving through Arizona until early 
next week...stay tuned. 


&& 


Aviation... 
no aviation concerns expected through at least 18 UTC Monday. 


High clouds with light surface winds (less than 7kt) are expected at 
all sites through at least 18 UTC Monday. Kphx/kiwa afternoon winds are 
expected to go light and variable...favoring northwest at under 
5-6kt briefly this afternoon/early evening. 


Aviation discussion not updated for amended tafs. 


&& 


Fire weather... 
Tuesday through Saturday... 
a rather dramatic change in weather will take place the middle to 
latter part of the week as a couple of weather systems moving 
through the western Continental U.S.. cooler temperatures...increasing moisture 
and a threat for showers and thunderstorms are expected Wednesday 
through the long Holiday weekend. 


&& 


Psr watches/warnings/advisories... 


Arizona...none. 


California...none. 


&& 


$$ 


National Weather Service Phoenix is on the internet at 


Weather.Gov/Phoenix 


Discussion...estle 
aviation...wanek 
fire weather...wanek