264 
fxus65 kpsr 180502 
afdpsr 


Area forecast discussion 
National Weather Service Phoenix Arizona 
950 PM MST Wednesday Mar 17 2010 


Synopsis... 
high pressure and above normal temperatures will continue through 
Thursday. A fast moving cold front will move through the region on 
Friday...bringing cooler temperatures and breezy conditions Friday 
and Saturday...with a slight chance of precipitation well east of 
Phoenix. High pressure will return through early next week for 
another warming trend. 


&& 


Discussion... 
WV and infrared imagery reveal a weak upper level trough taking shape off 
the coast of California this evening...around 33n 125w. System 
streaming some cirrus ahead of it over the sierras in California...but 
according to observation and forecasts...lacking Lower-Middle level moisture. 
Models show heights and thickness will begin to drop off overnight 
..lowering around 60m or so by tomorrow aft/eve. Surface temperatures 
trending down slightly compared to yesterday evening...now only 
about 2-5 degrees warmer most sites...with dew points in the upper 
30s to low 40s cwa-wide. 


This first short wave moves over the area tomorrow afternoon... 
allowing the next impulse and colder 500mb temperatures to filter 
in...broadening the trough over the southwest...with NAM/European model (ecmwf) showing 
a sharper trough than the GFS by 12z Friday. Inherited forecast drops 
maximum temperatures down several degrees for tomorrow...with additional cooling 
Friday...and this looks to be line with current observation and model runs. 


Previous discussion... 
Friday and Saturday... 
the system will be dry for the Phoenix metropolitan area...accompanied by 
gusty winds in conjunction with the frontal passage. Not out of the 
question to see some locally gusty winds up to 35 miles per hour...especially 
across portions of the lower Colorado River valley and south-central 
Arizona. Will maintain slight chance probability of precipitation for portions of zone 24... 
but it may be more of a morning threat with a much drier northwest 
flow gradually taking over on Friday night and into Saturday. Will 
expect modest cold air advection in the wake of this trough...but 
breezy and colder seems to be a stretch for zone 24 for Friday 
night. Local breezes Friday night could make minimum temperatures a bit 
more of a challenge...especially on the lower deserts. At any rate... 
Saturday appears to be the coolest day of them all with highs close 
to normal. 


Sunday and Monday... 
European model (ecmwf) and GFS similar in showing another Pacific Ridge driving 
onshore and into the southern rockies by 12z Monday. This will still 
be a dry period...and it will again lead to another warming trend. 
Only some minor tweaks to previous temperatures were needed. Above normal 
highs will again be expected. 


Tuesday and Wednesday... 
one more in the series of Pacific troughs is likely to sweep inland 
on Tuesday. Only this one will take a track through northern 
Baja California...and lift northeast through Arizona by the middle of the week. 
Timing differences are not so large...but the deeper GFS solution 
would suggest bringing in more clouds...and bumping up our chances 
of showers. 


&& 


Aviation... 
southeast California to south central Arizona...including 
kipl...kblh...kphx...and kiwa airfields...mostly clear skies and 
light winds through 03z Friday. 


Aviation discussion not updated for amended tafs. 


&& 


Fire weather... 
Friday through Tuesday... 
a sharp cold front will sweep south across Arizona from Utah Friday. Best 
chance of precipitation will be extreme eastern portions of southern 
Gila County. A dry airmass behind the cold front will cause humidity 
levels to fall Friday night...with minimum relative humidities 
dipping into the single digits over the weekend. Gusty west to 
northwest winds are also anticipated with the frontal passage...but 
there are no fire weather concerns at this time. Another high 
pressure system will begin to build over the region late Saturday 
and Sunday...which will provide much lighter wind and a warming 
trend into Tuesday. 


&& 


Psr watches/warnings/advisories... 


Arizona...none. 


California...none. 


&& 


$$ 


National Weather Service Phoenix is on the internet at 


Weather.Gov/Phoenix 


Discussion...Meyers/Sipple 
aviation...vasquez 
fire weather...vasquez/paddock