Weather

433 
fxus65 kvef 070336 
afdvef 


Area forecast discussion 
National Weather Service Las Vegas Nevada 
835 PM PST Sat Sep 6 2008 


Synopsis...high pressure and a very dry air mass will keep the 
forecast area sunny and warm the remainder of the weekend. Moisture 
will gradually increase from the south early next week supporting a 
slight chance of afternoon and evening thunderstorms over northwest 
Arizona Monday through Wednesday. 
&& 


Update...no updates for this evening...but have a few items to 
note. The latest met guidance has 107 for klas tomorrow...but the 
met has been averaging 1 to 2 degrees too warm the past several 
days. We'll likely raise the high temperature tomorrow to 105 but keep it 
below the excessive heat criteria of 106. Middle level moisture will 
increase a bit tomorrow and will enhance afternoon clouds. The 
latest NAM is more aggressive with its return of moisture on Tuesday 
afternoon with model soundings indicating precipitable water values above 1 inch 
into the Las Vegas Valley as it brings a weak impulse up the 
Colorado River valley during the day. One last item of 
note...Tropical Storm Lowell has formed in the eastern Pacific and 
is forecast to become a hurricane...but remain well to the south. 


Previous discussion...high pressure will remain in control through 
at least Sunday...with continued hot and sunny conditions and light 
winds. Water vapor imagery indicates a small area of cyclonic 
rotation just off the Southern California coast...and this mornings NAM and GFS 
had picked up on this feature quite well. This feature is prognosticated to 
eventually phase with a shortwave middle Tuesday/Wednesday...before 
ejecting and moving to the east towards the end of the extended 
period. In the meantime...the offshore midlevel circulation will 
result in light southerly flow over the forecast area. This will 
gradually bring an increase in moisture leading to a little more 
afternoon cumulus development with a slight chance of thunderstorms 
by Monday afternoon over the mountains of Mohave County. 
Temperatures will remain several degrees above normal although the 
increased moisture will take a degree or two off the maximum temperatures for 
Monday. 


Long term...models continue to agree on the presence of a baggy 
trough or weak cutoff low over the western states or eastern Pacific 
in the Wednesday through Saturday time frame...but this is about as 
far as the agreement GOES. The exact location and movement are still 
in question...as are how much moisture it can tap into and how 
quickly. The GFS is pretty much alone in phasing the low with a 
northern stream shortwave trough over the weekend...which would 
bring greater precipitation chances Friday and Saturday. Discounted this 
idea for now...and leaned more on the dgex and European model (ecmwf) which keep the 
low cut off from the westerlies and depict a much slower moisture 
advection process. With this in mind...raised probability of precipitation just a little for 
Friday and Saturday. Also lowered high temperatures a degree or two...but 
not as low as the GFS would suggest. 
&& 


Aviation...for McCarran...south to southwest winds could pick up to 
10 knots or so Sunday afternoon...otherwise...no significant weather 
is expected over the weekend. 


For the rest of southern Nevada...northwest Arizona...and southeast 
California...no significant weather is expected through the weekend. 
Skies will remain clear and winds will generally be from the south 
to southwest at around 10 knots with a few gusts near 20 knots 
during the late afternoon. 
&& 


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


$$ 


Czyzyk/Kennedy/Morgan 


Http://weather.Gov/lasvegas