Weather

170 
fxus65 kvef 101708 cca 
afdvef 


Area forecast discussion...corrected 
National Weather Service Las Vegas Nevada 
1000 am PDT Friday Oct 10 2008 


Synopsis...an unseasonably strong low pressure system will bring 
wind...colder temperatures and a chance of valley rain and mountain 
snow to the region today and over the weekend. The system will move 
off to the east early next week...allowing a warming trend and a 
return to mostly clear conditions. 
&& 


Update...sending an zone update generally just for sky since there 
is less clouds up north than forecast this morning. Temperatures are 
running 15 to 20 degrees cooler than 24 hours ago but some of that is 
just due to a cooler start this morning and expect that some of the 
slack will be made up with sunny skies and good mixing. The wind 
forecast could be tricky today. The Wind Advisory officially begins 
at noon but some areas to the west could start blowing earlier. The 
strongest winds in the Vegas valley itself will likely hold off 
until middle to late afternoon and then last through the evening. 
Also...will wait for the local nmm morning data before making a 
decision on the high wind watch northwest of the area and the Wind 
Advisory in the Sierra and Owens Valley. 
&& 


Aviation...for McCarran...a stalled cold front across the Las Vegas 
Valley will allow winds to generally be variable to east around 
6-8kts through 20z. A stronger push of colder air will begin to work 
south this afternoon and winds are expected to increase out of the 
southwest 15-25 kts with gusts of 35-40 kts ahead of this much 
stronger cold front. This second front will be marked by an increase 
in clouds with scattered-broken clouds expected at or above 10k feet. This second 
front is forecast to pass through between 9z and 12z Saturday of 
which afterwards winds should shift to the northwest at 15-20 kts 
with gusts of 30-35 kts. 


For the rest of southern Nevada...northwest Arizona...and southeast 
California...gusty winds will be the main issue across the area the 
next two days in association with a series of cold fronts. Expect 
gusty southwest winds of 35-40 kts this afternoon into tomorrow 
across the western San Bernardino County deserts and areas of 
blowing dust are likely which will reduce visibility to MVFR levels or 
lower. Gusty northerly winds of 35-45 kts generally are expected 
through tomorrow across the southern Great Basin and here as well 
blowing dust is possible reducing visibility. An upper level low dropping 
southward will bring a chance of showers to the southern Great Basin 
and eastern slopes of the southern Sierra this afternoon with a 
better chance tonight into tomorrow. Ceilings lowering to 6k-8k feet or 
lower are possible along with mts being obscured. Snow levels are 
forecast to lower 4500 feet north to 5500 feet south by Saturday 
night...however precipitation is expected to be showery in nature. 
&& 


Previous discussion...438 am PDT... 


Short term...very complex situation continues this morning so will 
just hit the high points. Wind advisories for the eastern Sierra 
slopes and the Owens Valley this morning are for weak downslope 
conditions as depicted in nmm and arw model cross sections. As the 
second cold front comes through there this afternoon/evening the 
downslope winds will end...but strong north winds will funnel down 
the Owens Valley...so left the advisory in place for the valley 
until early Saturday morning. Over the Mojave Desert...wind 
advisories and red flag warnings this afternoon and evening are for 
west to southwest winds ahead of the weakening first cold front 
which had nearly stalled over the Las Vegas Valley this morning. 
Over the Nevada test site and Death Valley...high wind watch this 
evening and tonight is for a period of strong north winds behind the 
second cold front. All this represents best guess for winds through 
early Saturday morning. Some products may need to be extended in 
time or expanded in area. Regarding precipitation...probability of precipitation have been raised 
to high chance/low likely over parts of the southern Great Basin 
tonight and Saturday...and this looks good given the rapidly rising 
isentropes and implied lift as the cold low moves in. Still not 
expecting heavy precipitation amounts as there is no moisture tap. 
Temperatures will start to crash today and continue on 
Saturday...with the coldest temperatures expected over the weekend. 


Long term...a tight surface pressure gradient will remain in place 
across the area on Monday afternoon between the departing system to 
our east and high pressure over the Great Basin. The Ely-eed surface 
p-gradient is prognosticated to be around 10 mb...enough to keep gusty north to 
northeast winds around through the day especially down the Colorado 
River valley where a lake Wind Advisory will likely be needed. With 
a cool northerly flow in place temperatures will remain below normal. 


By Tuesday surface p-grads are expected to weaken across the area but 
there still looks to be enough of a gradient to keep it breezy down 
the Colorado River valley. Otherwise temperatures will begin to rebound 
across the area as an upper ridge pokes in from the west. This ridge 
will be knocked down by a shortwave trough that moves by on 
Wednesday morning...however the ridge looks to rebuild by Thursday 
as the trough departs to the east. With 500 mb heights prognosticated to 
approach 588 dm near Las Vegas by Thursday...temperatures will easily reach 
above normal readings and remain warm into Friday. 


Our next system with the potential for precipitation looks to be a 
shortwave trough embedded within the southern branch of the 
jetstream. Both the 00z runs of the European model (ecmwf) and operational GFS show 
this feature but disagree on timing. For now...I have brought in an 
increase in clouds as early as Friday afternoon but it looks like 
the better shot at precipitation will come in a short window when it passes 
through sometime Saturday. Given the nature of this system being a 
southern stream system it looks to have a better moisture tap with 
it but lack enough upper support to be a wind event. 
&& 


Fire weather...strong west to southwest winds will develop across 
much of the Mojave Desert again today. Low relative humidities are 
also expected...so issued a red flag warning for az102...ca228 and 
nv465. Higher humidities are expected over the weekend due to 
unseasonably cold temperatures. On Monday...low relative humidity levels are 
expected areawide...however the only area that could see conditions 
approach critical levels would be along the Colorado River valley 
where gusty northerly winds are expected to linger. && 


Vef watches/warnings/advisories... 
Nevada...Wind Advisory zones 16...20 and 22 today from noon until 
midnight PDT. 
High wind watch zones 14 and 17 from late this afternoon 
through early Saturday morning. 
Red flag warning fire zone 465 today from noon until 10 PM PDT. 
Arizona...Wind Advisory zones 1 and 3 today from noon until midnight MST. 
Red flag warning fire zone 102 today from noon until 10 PM MST. 
California...Wind Advisory zone 519 in effect until 4 PM PDT. 
Wind Advisory zone 520 in effect until 6 am PDT Saturday. 
Wind Advisory zones 523 through 526 today from noon until 
midnight PDT. 
High wind watch zone 522 from late this afternoon through early 
Saturday morning. 
Red flag warning fire zone 228 today from noon until 10 PM PDT. 
&& 


$$ 


Salmen/gorelow/Morgan/stachelski 


Http://weather.Gov/lasvegas 

National Weather Service Glossary of Abbreviations

Non-Expanded Version (with abbreviations)