900 
fxus65 kvef 131101 
afdvef 


Area forecast discussion 
National Weather Service Las Vegas Nevada 
400 am PDT Monday Oct 13 2008 


Synopsis...the unseasonably cold low pressure system which moved 
over the area this weekend will shift to the east today and Tuesday 
as high pressure builds into the southwest. Continued cool 
conditions and gusty winds will be seen today and Tuesday before 
temperatures rebound above normal by the latter part of the week. 
&& 


Short term...the base of the upper low could be seen on water vapor 
imagery over northwest Arizona at 10z. Recent surface analyses 
showed the pressure gradient increasing to 11 mb between Ely and 
Needles as the surface high strengthened over northeast Nevada. 
This will combine with deep northerly flow and subsidence on the 
back side of the system to produce gusty north to northeast winds 
around 30 miles per hour across most of the area today. The Colorado River 
valley will see gusts of 40-45 miles per hour and the Wind Advisory previously 
issued remains in effect today. The southern branch of the upper low 
is forecast to close off and slowly move across northern Arizona 
into northwest New Mexico tonight and Tuesday. The flow aloft 
decreases and becomes more northwesterly Tuesday but the surface 
gradient will continue to support gusty north winds down the 
Colorado River valley. A weak shortwave trough moving through the 
Pacific northwest Wednesday will maintain a northwest flow aloft but 
temperatures will moderate and winds will become generally light. 
Although temperatures should increase around 5 degrees today...record low 
maximum temperatures will still be a possibility again for Las Vegas...Barstow 
and Needles. Several degrees of additional warming Tuesday and 
Wednesday will help readings rebound back to normal. 


Long term...an upper ridge will slide eastward across the 
southwestern Continental U.S. Allowing for warm weather to make a comeback. The 
GFS/ECMWF/Gem/dgex are in good agreement with temperatures warming some 3 
to 6 degrees over Wednesday reaching above normal levels across the 
area. By Friday the ridge will slide east but this should be the 
warmest day for the eastern half of the area as 500 mb heights rise 
to or above 588 dm. This would support highs in the lower elevations 
of the Mojave Desert generally in the upper 80s and lower 90s. 


Somewhat decent agreement in the models for Saturday and beyond. 
However the main challenge has been the run to run inconsistencies 
with the models. The first wrinkle comes Friday night as the 00z GFS 
and 06z dgex still advertise a southern stream shortwave to move 
northeast from socal towards southern Utah. The 00z GFS suggest some 
showers are possible across the Mojave Desert with this feature. 
Clouds were tweaked up...but left the forecast dry due to the 
constant model flip flopping. Another trough will move through on 
Sunday/early Monday...but again there is disagreement as to whether 
this will be a northern stream feature as the European model (ecmwf) shows or 
southern stream feature as the GFS and dgex show. Either way it 
looks dry. Overall expect some cooling over the weekend as the ridge 
retreats eastward and heights lower. The 00z GFS and European model (ecmwf) both 
trend towards ridging for the middle of next week which would 
support a warming trend...that said the 12z European model (ecmwf) was a Stark 
contrast with a deep closed low heading towards Vegas Tuesday...for 
now...leaned dry and warm. 
&& 


Aviation...for McCarran...gusty north winds are expected today into 
tonight thanks to a tight surface pressure gradient across the area. 
Wind gusts should be greatest this afternoon with gusts of 25-30 kts 
expected. A clear sky today and tonight. 


For the rest of southern Nevada...northwest Arizona...and southeast 
California...the main issue today into tonight will be gusty north 
winds mainly down north-south oriented valleys with the strongest 
winds likely this afternoon/evening down the Colorado River valley 
where gusts of 25-35 kts are expected...including at keed. Moderate 
mechanical turbulence will be likely across the area with winds 
forecast to be near 30 kts around 10k feet mean sea level. Winds will lessen 
somewhat by tonight. A clear sky is expected. 
&& 


Fire weather...as the trough begins to move out of the district 
today...north flow will increase across much of the area. These 
north winds will be enhanced over the north wind prone 
areas...especially the lower Colorado River valley. Afternoon 
relative humidity values will remain low...with much of the southern 
deserts below 15 percent. Due to the gusty winds and low humidity 
values...a red flag warning has been issued for the Colorado River 
valley. See section below or current fire weather products. && 


Vef watches/warnings/advisories... 
Nevada...red flag warning from 11 am this morning to 8 PM PDT this 
evening for nvz466. 
Wind Advisory from 10 am this morning to 8 PM PDT this evening 
for nvz021. 
Arizona...red flag warning from 11 am this morning to 8 PM MST this 
evening for azz101. 
Wind Advisory from 10 am this morning to 8 PM MST this evening 
for azz002-036. 
California...red flag warning from 11 am this morning to 8 PM PDT this 
evening for caz229. 
Wind Advisory from 10 am this morning to 8 PM PDT this evening 
for caz527. 
&& 


$$ 


Adair/stachelski 


Http://weather.Gov/lasvegas