128 
fxus65 kpsr 182120 
afdpsr 


Area forecast discussion 
National Weather Service Phoenix Arizona 
220 PM MST Thursday Mar 18 2010 


Synopsis... 
a fast moving cold front will move through the region 
Friday...bringing cooler temperatures and breezy conditions on 
Saturday...along with a slight chance of showers well east of 
Phoenix. High pressure will return early next week bringing dry 
weather and a warmup. Yet another fast moving Pacific weather system 
will bring a slight chance for showers to Arizona next Tuesday into 
Wednesday...along with cooler temperatures. 


&& 


Discussion... 
visual satellite imagery shows cloud free conditions across the 
entire County Warning Area. Some middle level clouds were moving across the northern 
portion of Arizona. Temperatures are similar to yesterday at this 
time although some cooling is noted along the Colorado River valley 
with most showing high 70s to low 80s. Water vapor imagery shows a 
developing NE-SW oriented trough developing across northwest Nevada with 
dry air to the west of the trough over northern California. Both GFS 
and European model (ecmwf) shows this trough deepening as it drops south over 
southern Nevada. Both models agree with the placement of the low 
pressure center over the Colorado River valley by 12z Friday. This 
rapidly deepening system will generate tightening gradients across 
extreme southeast California...and hence northerly winds will pick up and 
eventually mix down to the surface...generally centered over the 
Colorado River valley. For that reason we issued a Wind Advisory 
beginning 8 am Friday until 5 PM MST/PST Friday for the valley. We 
also added some blowing dust for the daylight period for the river 
zones as this will likely be a hazard for drivers. 


The trough...and associated cold front...should be rolling through 
west and central Arizona around middle day Friday. North winds will 
spread across the County Warning Area as this system rapidly moves through during 
the day. Winds should be breezy across areas east of the Colorado 
River valley but are not expected to reach the advisory levels that 
will be seen along the Colorado River valley. 


Both the GFS and European model (ecmwf) seemed to speed up the system and accordingly 
led to a drop in anticipated high temperatures for Friday. Therefore we 
dropped the highs about 5 degrees...with now expecting only 74 for 
Phoenix...a 5 degree drop from the previous forecast package. Also 
raised the probability of precipitation just a bit across north and east extremes of the County Warning Area 
but still only in the slight chance for the higher terrain and 
southern Gila County. 


A ridge will move over the area Saturday and Sunday leading to some 
warming and dry weather for the weekend. Both the GFS and European model (ecmwf) 
indicate the next system to start to impact the region by Tuesday. 
The GFS is aggressively developing a cutoff low moving over northern 
Baja California California whereas the European model (ecmwf) shows it more as a short wave off 
of a larger trough centered over the Idaho vicinity. European model (ecmwf) passes 
the trough over Arizona quickly with not much weather impact whereas 
the GFS drops the cutoff low southeast over Sonora Mexico. 
Curiously...the two models converge later in time...on 
Wednesday...agreeing with development of another larger scale Great 
Basin low...this one centered over The Four Corners by Wednesday. 
Most of the energy associated with this system looks to be centered 
to the north and east of our County Warning Area. Accordingly...at this time not expecting a 
lot of weather with this system other than the typical gusty 
winds...primarily on Wednesday. 


&& 


Aviation... 
kipl...kblh...and surrounding airfields... 
expect mostly clear skies and light west winds through 06z Friday. 
Wind speeds will begin to increase out of the northwest with 
approaching cold front. After frontal passage...expect gusty north winds 20-30 
kts with occasional gusts to 35 kts. 


Kphx...kiwa...and surrounding airfields... 
expect mostly clear skies and light diurnal winds through 06z 
Friday. Good confidence an east breeze will set up tonight. Upper 
trough and cold front will move through our area early Friday 
afternoon...with scattered/broken clouds above 10 thousand feet and westerly winds 
10-20 kts. 


Aviation discussion not updated for amended tafs. 


&& 


Fire weather... 
Saturday through Wednesday... 
a dry airmass associated with another high pressure system settles 
over the region Saturday...behind the departed cold front...which 
will cause minimum relative humidities to dip into the single digits 
across Lower Desert locations through Monday. Breezy northerly winds 
will slowly diminish Saturday. Lighter winds and a warming trend are 
anticipated Sunday into Monday...before another low pressure system 
tracks across the region Tuesday into Wednesday providing the area 
with a slight chance of precipitation. 


&& 


Psr watches/warnings/advisories... 


Arizona...Wind Advisory from 8 am to 5 PM MST Friday for azz020-025. 


California...Wind Advisory from 8 am to 5 PM PDT Friday for caz031. 


&& 


$$ 


National Weather Service Phoenix is on the internet at 


Weather.Gov/Phoenix 


Discussion...waters 
aviation...Sipple 
fire weather...paddock