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Area forecast discussion 
National Weather Service Las Vegas Nevada 
350 PM PDT Thursday Aug 28 2008 


Synopsis...a large area of high pressure will result in above normal 
high temperatures tomorrow. An unseasonably strong weather system will 
affect the area over the Labor Day weekend...bringing a chance of 
thunderstorms...breezy conditions...and significantly reduced 
temperatures by Labor Day. 
&& 


Short term...a hot and dry day across the forecast area as satellite 
imagery indicates clear skies except for developing cumulus across southern 
Mohave County. This will be the case on Friday as high pressure 
continues to dominate the area...with models indicating the high 
centered right over southern Nevada the majority of the day. Expecting 
temperatures to be just below excessive heat criteria again...with 
slight cooling aloft indicated by models...but forecast may have to be 
bumped up a degree or two if surface dewpoints decrease significantly. 
Big pattern changes will be under way during the Labor Day 
weekend...with strong model agreement that an unseasonably strong 
weather system will cross the Great Basin...resulting breezy 
conditions...and temperatures dropping approximately 15 degrees 
areawide. Additionally...as the high center transitions to the 
east...the door will open again for monsoonal flow to increase 
moisture...especially across Lincoln...Clark...Mohave...and eastern San 
Bernardino counties Saturday and early Sunday. This coupled with the 
dynamics of the approaching system may result in conditions favorable 
for organized convection...especially across eastern Lincoln and Mohave 
counties where wind shear magnitude is the greatest. Lastly...it 
should be noted that breezy conditions are expected this weekend...and 
right now winds along the Colorado River zones are just below lake Wind 
Advisory...so may have to consider a lake Wind Advisory for the Holiday 
weekend if models trend any stronger. 


Long term...Monday to Thursday...good model agreement with the system 
coming through during the Labor Day weekend. Bulk of the active weather 
will be Saturday through early Monday. The cold front will be passing 
though the County Warning Area early Monday morning bringing with it temperatures that 
will be below normal for Monday and Tuesday. Have lowered temperatures 
a degree or two as bias corrected guidance points this way. The system 
looks to be deeper and slower than previously thought with the Gem 
being the deepest/slowest. As a result have increased the probability of precipitation and 
cloud cover in Mohave County for Monday. Another concern is for the 
winds. Have kept the breezy conditions in for Mohave County Monday 
ahead of the front. For now not sure about breezy conditions behind the 
front as forecast pressure gradient is marginal for this. Did upped the 
winds for the mountain zones of Inyo County Monday morning as the jet 
maximum will be transiting the area then as it rounds the base of the 
trough. After Monday conditions settle down as weak zonal gives way to 
weak northwest flow as ridge off the coast builds with a broad trough 
over the middle Continental U.S. And temperatures increase. 
&& 


Aviation...for McCarran...very weak and variable winds for the rest 
of the afternoon. Late tonight a southwest to west wind sets up 
under 10 knots. Friday appears to be a repeat of today with light 
and variable winds in the afternoon. A significant change in the 
weather is expected this weekend as a strong system approaches the 
area. Thunderstorms are possible Saturday and Sunday. 


For the rest of southern Nevada...northwest Arizona...and southeast 
California...few to scattered high clouds through Friday. Winds will light 
and variable and follow local diurnal patterns. A significant change 
in the weather is expected this weekend as a strong system 
approaches the area. Thunderstorms are likely Saturday and Sunday 
through out the area. 
&& 


Fire weather...with a strong upper level trough axis prognosticated to swing 
across the area Sunday and Monday we will need to keep a close eye 
on winds. This trough axis will bring in significantly drier air to 
the area once it passes through and winds look to be gusty 
especially in favored spots ahead of and especially behind the 
passage of the trough axis. The main concern will be the duration of 
winds as well as just how strong they may get. As of now...areas 
across the southern Great Basin and parts of Inyo County look to 
have the greatest possibility of meeting red flag warning criteria 
or get at least close to it. 
&& 


Vef watches/warnings/advisories... 
Nevada...none. 
Arizona...none. 
California...none. 


$$ 
Kennedy/Jacques 


Http://weather.Gov/lasvegas