982 
fxus65 kvef 081727 
afdvef 


Area forecast discussion 
National Weather Service Las Vegas Nevada 
1026 am PDT Friday Aug 8 2008 


Synopsis...moist and unstable air will remain over portions of 
southern Nevada...northwest Arizona and eastern San Bernardino 
County in southeast California through Saturday resulting in 
isolated to scattered thunderstorms. A drier southwest flow is 
forecast to develop by the latter part of the weekend and continue 
into early next week with thunderstorms confined to primarily 
northwest Arizona. 
&& 


Update...current thermodynamic analysis from Storm Prediction Center indicated quite a 
bit of cape and low lifted index over eastern San Bernardino County. 
Nam12 also indicates a fair amount of moisture and instability there 
as well. Updated to increase probability of precipitation over eastern San Bernardino 
County. Otherwise forecast looks good with dry and stable air across 
much of the western portion of the forecast area. 
&& 


Aviation...for McCarran...winds will range in direction from south 
to southeast today with speeds generally from 8-10 kts and 
occasionally gusting to 20 kts in the afternoon. Cloud coverage will 
increase as cumulus develops through the late morning and afternoon. 
Isolated thunderstorms are possible around the Las Vegas Valley but 
greater coverage expected south and east of the Airport. At the 
Airport itself...the primary threat today will be gusty...erratic 
winds from thunderstorm outflow boundaries. Affected approach 
corridors today are Peach Springs...Mormon Mesa and Daggett. 


For the rest of southern Nevada...northwest Arizona...and southeast 
California...scattered thunderstorm coverage expected mainly east of 
Las Vegas but scattered storms could also form over eastern San 
Bernardino County as far west as kdag. Only a slight chance of 
storms over the northwest forecast area. Primary threats continue to 
be heavy rain and gusty...erratic winds. The greatest cloud coverage 
will be over the eastern half of the area. Surface winds gusting to 
25 kts in some areas today. 
&& 


Previous discussion...350 am PDT Friday Aug 8...short term...considerable 
debris clouds over the eastern half of the County Warning Area with basically clear 
skies over the western half. Although convection has 
ended...isolated activity possible early this morning across mainly 
eastern San Bernardino/Mohave counties thus will not mention late 
morning start of convect in these zones. Slow increase in southwest 
flow aloft to continue to dry the western portion of the County Warning Area today 
into the weekend with drying slowly taking place over the eastern 
portion. However...for today best dynamics/ instability remains over 
Lincoln/Clark/Mohave and the eastern portion of San Bernardino 
County...for isolated/scattered afternoon/evening thunderstorms. The 
possibility of heavy rain continues as precipitable water values remain around 1.5 
inches. Main concern though is debris clouds will inhibit initial 
heating and thus will look for initial convection to be around the 
edges of the current cloud cover. With increasing southwest flow 
aloft...drying as mentioned to begin to move over the eastern 
portion on Saturday with convection mainly over the eastern portion 
of Lincoln/Clark/Mohave counties and then for Sunday...mainly Mohave 
County. Temperatures to be near to slightly below normal through the 
weekend...depending on the locations of the afternoon 
clouds/thunderstorms. 


Long term...in the wake of a trough axis that swings across the Pacific 
northwest and norcal/northern Nevada on Sunday night/Monday morning heights 
will begin to rebound across the western Continental U.S. On Monday. We should 
still see enough of a dry west flow aloft across the County warning forecast area and thus 
they only moisture/instability that supports keeping in any probability of precipitation is 
across Mohave County and even here we may just see some cumulus 
build ups at best. Although the European model (ecmwf) rapidly tries to rebuild the 
western Continental U.S. Ridge by Monday afternoon...the Gem and the GFS 
ensemble mean delay this until Tuesday. The operational GFS keeps 
heights much flatter on the 6z run. Given the models are insisting 
in bringing a cold front as far south as Florida in August...one 
would have to think the upper level pattern in the west would 
support a highly amplified ridge. Thus have leaned towards the 
Gem/GFS ensembles/European model (ecmwf) for the long range. This would support 500 
mb heights at/above 588 dm...which would support highs at least 2 to 
4 degrees above normal. Just how quick any monsoonal moisture 
returns is still questionable...but a return northward of moisture 
looks possible by Thursday...which will once again bring back the 
prospects for convection to much of the area. 
&& 


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


$$ 


Harrison/Salmen/Jensen/stachelski 


Http://weather.Gov/lasvegas