Area forecast discussion 
National Weather Service Phoenix Arizona 
805 am MST Friday Nov 21 2014 


Synopsis... 
a Pacific weather system will move quickly east across Arizona 
today...bringing mostly cloudy skies...slightly cooler temperatures 
and a slight chance of showers. Mostly clear and dry conditions with 
near normal temperatures will return over the weekend...then linger 
into early next week. Higher pressure aloft will build into the 
Desert Southwest by the middle of next week allowing for high 
temperatures to climb a few degrees above seasonal normals. 


&& 


Discussion... 
quick updates were made to forecasts to include a slight chance of 
showers and thunderstorms across a large swath from southeast California to 
south central Arizona...including Phoenix. One look at the upper air data 
sort of gave US the heebee jeebees. The approaching small...but 
dynamically strong trough...with limited moisture...has the potential 
to produce at least a slight chance of high based showers and 
thunderstorms. Rapidly cooling middle level temperatures today... 
strong 500 mb/300 mb height falls directed at Gila Bend...and strong 
difluence aloft will try to squeeze the atmosphere dry so to speak. 
Earlier this morning there were a number of lightning strikes in 
southeast California...and it was raining lightly in Yuma at 7 am. Strong 
height rises along the West Coast suggest this is a fast moving 
system...and precipitation probabilities should diminish rapidly later this 
afternoon...clearing overnight. 


Otherwise...remainder of forecasts for the weekend look OK. 




Parts of previous discussion...530 am MST... 
as the upper low quickly exits to the east/southeast tonight...southeastern 
California and Arizona will come under a cool...dry and subsident northwesterly flow 
aloft. Some high clouds will spread in from the northwest Saturday 
for partly to mostly sunny skies...and high temperatures will stay near 
seasonal normal levels with a high of 72 forecast for Phoenix. 


For Sunday into the middle of next week...guidance agrees that a dry 
northwest flow aloft will be the rule each day...as high pressure 
gradually builds into the area for mostly sunny days and mostly 
clear nights. Some shortwave energy passing through The Four Corners 
area Sunday will bring another shot of cooler air to the region... 
allowing temperatures Monday to fall back slightly...mainly over south 
central Arizona. Highs will drop back into the upper 60s over the lower 
central deserts Monday with Phoenix to see a high around 69. After 
that...a slow warming trend is expected with highs rising into the 
middle 70s by Wednesday over the warmer lower deserts under mostly 
sunny skies. 


&& 


Aviation... 
south-central Arizona including kphx...kiwa...and ksdl... 
cloud bases will continue to lower through late morning down to 
about 12 kft mean sea level before clearing from west to east after 23z. 
Anticipate areas of virga with precipitation reaching the ground only over 
the higher terrain. Winds will be light favoring east before 
favoring northwest by late afternoon/early evening. 


Southeast California and southwest Arizona...including kipl and 
kblh... 
scattered-broken cloud bases at 12 kft mean sea level can be expected this morning along 
with some few-scattered 6-8 kft mean sea level before clearing by middle afternoon. 
Cannot rule out a stray thunderstorm but too isolated to reflect in 
the tafs. Otherwise just some virga. Expect northwest and north wind 
directions with occasional local gusts of 15-20 kts. 


Aviation discussion not updated for amended tafs. 


&& 


Fire weather... 
..dry and windy Sunday southeast California and southwest 
Arizona... 
Sunday through Thursday... 
strong northerly winds will develop over portions of southeast 
California and southwest Arizona Sunday as a dry front pushes 
through the forecast area. Much drier air will move in as well. 
Conditions will flirt with critical thresholds Sunday 
afternoon...mainly near the lower Colorado River valley. Winds will 
stay elevated overnight at ridgetops but will weaken on the valley 
floors. Expect lighter winds Monday with some minor breeziness 
resuming over and near the lower Colorado River valley. Light winds 
will prevail Tuesday through Thursday. Expect near to somewhat below 
normal temperatures through Tuesday before warming at lest a few 
degrees Wednesday with little change Thursday. Humidities will 
remain low with some improvement possible Thursday. 


&& 


Psr watches/warnings/advisories... 


Arizona...none. 


California...none. 


&& 


$$ 


Visit US on facebook...twitter...and at weather.Gov/Phoenix 


Discussion...vasquez/cb 
aviation...aj 
fire weather...aj 



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