412 
fxus65 kvef 110400 
afdvef 


Area forecast discussion 
National Weather Service Las Vegas Nevada 
857 PM PDT Friday Oct 10 2008 


Synopsis...an unseasonably strong low pressure system will affect 
the weather over the region through Sunday. In addition to wind... 
colder temperatures and a chance of valley rain and mountain snow is 
expected. The system will move off to the east early next week... 
allowing a warming trend and a return to mostly clear conditions. 
&& 


Update...surface front extended from Cedar City to desert rock to 
the central Owens Valley at 830 PM. Ahead of the front winds are 
borderline advisory level with the exception of western and central 
San Bernardino County where gusts have consistently tapped into the 
40-45 miles per hour range. Over Clark and Mohave counties gusts have remained 
between 30-40 miles per hour. Lax-las gradient is less than 10mb now but may 
intensify as the front presses nearer so will allow those advisories 
to continue. Behind the front...pressure gradient from tph-las has 
intensified to 10 mb and northerly gusts have exceeded 60 miles per hour in the 
Owens Valley and on the Nevada test site. None of the MOS guidance 
numbers suggest frontal passage tonight through Las Vegas which is curious. As 
the upper low bottoms out over the next few hours a frontal wave may 
form to our north which could stall the southward progress of the 
cold front briefly but I dont see anything to delay its passage 
later than the early morning hours. In fact one concern for tonight 
is the possibility of an hour or two of warning level winds with 
frontal passage before settling down into 30-40 miles per hour gusts for a few more hours 
after that. If the dra-las gradient gets up to 3 or 4 mb I will 
probably punch out a quick upgrade to the advisory. Otherwise 
everything inherited from day shift is on track: windy tonight... 
becoming much cooler with scattered showers and snow level falling 
to near 5000 feet tomorrow. -Runk- 


Previous discussion...from 345 PM PDT...short term...the weekend 
weather event continues to unfold as an unseasonably strong low 
pressure system heads towards the area. Surface observations 
indicate a surface cold front has passed south through the Bishop 
area with the Airport measuring a gust of 52 miles per hour. Ahead of the 
front...southwest winds are increasing across much of the County Warning Area with 
gusts exceeding 40 miles per hour across portions of the Mojave Desert. Expect 
that other sites within the warning and advisory areas will soon 
begin to verify. The nmm is forecasting an extended period of strong 
north wind behind the front over Death Valley and Esmeralda and 
central Nye counties late this afternoon and overnight. Upgraded the 
high wind watch to a High Wind Warning for these areas. 
Also...issued a Wind Advisory for Lincoln and southern Nye counties 
for north wind and for the Las Vegas Valley for northwest winds 
early Saturday morning...mainly for the northern portions of the 
valley. Isolated gusts to near high wind criterion possible in the 
most wind prone areas. See rnonpwvef for details. The whole system 
is forecast to settle over the area tonight with the low centered 
just north of Vegas. Central Nye and Lincoln counties are in the 
best area for snow. Thinking that amounts will be generally light 
and below advisory levels. Most notable will be the colder 
temperatures. Highs for Saturday and Sunday 15 to 20 degrees below 
normal with lows around 15 cooler than normal. 


Long term...low pressure center will shift northeast into northern 
Utah Sunday with residual moisture remaining in place over eastern 
Lincoln counties. Expect quantitative precipitation forecast to remain light and have kept the 
current 20 probability of precipitation. Heights and thickness values will rise on 
Sunday...but with continued northerly winds do not see a significant 
temperature jump. Kept temperatures well below normal and only 
increased them around 3-5 degrees above Saturday. Surface high 
pressure is forecast to strengthen over northwest Nevada and 
eventually shift south and east. This will allow for tightening 
surface pressure gradients and increased wind speeds...especially 
down the Colorado River valley beginning Sunday night and continuing 
into midday Tuesday. Its likely that advisories will be need 
sometime during that time frame. Additional temperatures rises will 
be seen Monday...but Tuesday and Wednesday will see bigger increases 
and temperatures are forecast to rise to near normal by midweek. 
&& 


Aviation...for McCarran...southwest winds are expected to increase 
this evening ahead of a strong cold front currently moving through 
the Great Basin. Southwest winds of 20-30kts with gusts around 40kts 
are expected through 09z. The cold front is forecast to move through 
the valley between 08z-10z tonight with winds shifting to a 
northwest direction around 15-25kts and occasional gusts near 35kts. 
This second front will be marked by an increase in clouds with 
scattered-broken clouds expected at or above 10k feet. 


For the rest of southern Nevada...northwest Arizona...and southeast 
California...a strong cold front currently moving through the Great 
Basin will continue to push south this evening and is expected to 
reach southern Clark...southern San Bernardino...and southern Mohave 
counties around 12z Saturday. Southwest winds ahead of the front are 
expected to be around 25-35kts with gusts around 40kts. Behind the 
front areas in the Owens Valley can expect to see north winds 
25-35kts and gusts over 45kts through 08z. Localized blowing dust 
will occur with visibilities dropping to below 5sm. 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. 
&& 


Fire weather...a red flag warning continues for az102...ca228 and 
nv465 through 10 PM this evening. Fire weather concerns will be 
minimal on Saturday with much colder air in place. 
&& 


Vef watches/warnings/advisories... 
Nevada...High Wind Warning until 7 am PDT Saturday for nvz014. 
Red flag warning until 10 PM PDT this evening for nvz465. 
Wind Advisory until midnight tonight for nvz016-020-022. 
Wind Advisory from 3 am to 12 PM PDT Saturday for nvz020. 
Wind Advisory until 7 am PDT Saturday for nvz015-017. 
Arizona...red flag warning until 10 PM MST this evening for azz102. 
Wind Advisory until midnight MST tonight for azz001-003. 
California...High Wind Warning until 11 PM PDT for caz520...then a Wind 
Advisory until 6 am PDT Saturday. 
High Wind Warning until 7 am PDT Saturday for caz522. 
Wind Advisory until midnight PDT tonight for caz523>526. 
&& 


$$ 


Salmen/gorelow 


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