706 
fxus65 kfgz 282210 
afdfgz 


Area forecast discussion 
National Weather Service Flagstaff Arizona 
310 PM MST Thursday Aug 28 2008 


Synopsis....a high pressure ridge building in along the Arizona 
Utah border will produce a more stable and drier pattern with a 
reduction in shower and thunderstorm activity across much of the 
Northland through Friday. A trough pattern is expected to move into 
Arizona for the weekend producing a chance for strong to severe 
thunderstorms along with heavy rain through Monday. Overnight 
thunderstorm activity across much of the Northland is a strong 
possibility for both Saturday and Sunday nights. 


&& 


Discussion...a drier and more stable airmass has moved into 
northern Arizona from the high pressure ridge building in along the 
Arizona Utah border. This drier airmass has limiting convection to 
the highest elevation areas today with observed dewpoint 
temperatures decreasing by 10 to 20 degrees from the morning 
observations in our northern most forecast zones. Expect this dry 
airmass to move a bit further south on Friday...limiting chances for 
showers and thunderstorms across much of northern Arizona. The best 
chances for precipitation on Friday will be in the White Mountains 
with widely scattered thunderstorm activity. 


Saturday through Monday...a wild weekend is in the forecast as a 
short wave trough moves into Arizona from the west and the risk 
increases for severe thunderstorms and heavy rain showers. Starting 
on Saturday...a short wave trough approaches Arizona from the west 
bringing up additional moisture and instability from the south and 
increasing our chances for showers and thunderstorms across northern 
Arizona. By Sunday...as the trough moves into Arizona forecast 
models show an upper level low moving up from Baja California California. A 
warming of the 500 mb temperatures is shown in the models for 
Sunday. This warming is likely due to subsidence on the western side 
of the upper level low as it transits through the state. This upper 
level warming may produce a stabilizing effect on the airmass and 
cause a reduction in chances for showers and thunderstorms across 
our western forecast zones. For now we have a 40 to 50 percent 
chance of showers and thunderstorms across all of northern Arizona 
..these chances for precipitation for Sunday may change as the 
system gets closer. On Monday...the trough moves through 
Arizona...sweeping out the monsoon moisture and producing another 
active and possibly severe thunderstorm day. 


Tuesday through Thursday...a dry and stable airmass moves in behind 
the short wave trough with a marked reduction in showers and 
thunderstorms expected. 


&& 


Aviation...for the 00z package...expect widely scattered 
thunderstorms to continue across areas south of a line from St Johns 
to Bagdad through 02z...otherwise VFR conditions are expected 
through 18z Friday. After 18z Friday expect widely scattered thunderstorms 
to develop across areas south of a line from St Johns to Bagdad 


&& 


Fire weather...see fire weather forecast (fwffgz) for discussion of 
days 1 and 2. 


Sunday through Tuesday...an early season low pressure system will 
likely move through the Great Basin on Sunday and Monday. While 
moisture is expected to linger through Monday...the airmass may 
become too stable to support widespread storm development on Sunday. 
Scattered afternoon storms are forecast for Monday...with more 
isolated activity on Tuesday. 20 foot wind forecast for Sunday and 
Monday afternoon is for southwest winds 10 to 25 miles per hour with gusts to 
30 miles per hour. 


&& 


Fgz watches/warnings/advisories...none. 


$$ 


Public...............bohlin 
aviation/fire weather.....41 


Visit weather.Gov/Flagstaff for northern Arizona weather information.