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fxus65 kvef 231135 
afdvef 


Area forecast discussion 
National Weather Service Las Vegas Nevada 
335 am PST sun Nov 23 2008 


Synopsis...dry and mild conditions will continue today and Monday 
before a dramatic change in the weather develops Tuesday through 
Thanksgiving weekend. The first in a series of Pacific storms will 
reach the West Coast Tuesday then move inland Tuesday night and 
Wednesday...bringing a good chance of rain to the valleys and snow 
to the mountains. A brief break between storms is expected 
Thanksgiving day before a second Pacific system brings another 
chance of rain and snow to the region next weekend. 
&& 


Short term...satellite shows that cirrus has been suppressed to 
areas south of Interstate 15...with clear skies farther north. The 
cirrus kept temperatures down more than expected Saturday...so 
expect a bit of a rebound today with full sunshine. A weak ridge of 
high pressure will control our weather through tonight...then the 
trough of low pressure just west of 140w this morning will come into 
the picture. There is still a lot of spread among the models with 
the details of how this storm will evolve...with the NAM still 
shallowest and fastest...the European model (ecmwf) still slowest...and the GFS still 
in between. Forecast will again lean towards the GFS...but it must 
be noted that the slower European model (ecmwf) scenario remains plausible /the same 
cannot be said for the NAM/. The GFS splits the trough later today 
/which looks very good given current water vapor imagery/ and brings 
the southern portion to 34n 130w as a closed low Monday afternoon. 
Meanwhile...a finger of moisture from the intertropical convergence 
zone lifts north along 120w due to the influence of the digging low. 
The low pulls this moisture up its eastern side Monday night as it 
moves slowly east...causing precipitation chances to break out over 
California. The precipitation chances spread over our entire County warning forecast area Tuesday 
as the low slowly tracks east and finally reaches the Southern 
California coast Tuesday night. Due to the warm tropical tap snow 
levels will start out quite high...but if the moisture plume orients 
just right...the higher elevations of the Sierra could see 
significant snow accumulations as early as Tuesday. Confidence in 
the orientation and timing are not high enough to justify a watch 
yet...but will beef up wording in the Special Weather Statement. 
Assuming the GFS timing is right...temperatures will start to drop 
off on Tuesday...but this would be postponed until Wednesday if the 
slower European model (ecmwf) is right. 


Long term...again models start out the extended...Wednesday...in 
good agreement concerning the first system to track trough he area 
Wednesday and Thursday. It appears this system will grab a decent 
amount of moisture and bring widespread rain and snow. Latest model 
runs have the track of the low further south than 24 hours ago. 
However...with the good moisture source and general uplift / 
instability think the track variations will not make too big a 
difference. Snow levels still stay up there around 6000 feet or 
higher. Significant accumulations are likely in the Sierra and 
Spring ranges and higher elevations in Lincoln County. This will be 
addressed in this mornings severe weather potential statement and Special Weather Statement. I did add in a slight chance 
for thunderstorms in our far south areas for Wednesday and early 
Thursday. The low will track a cold pool over that area and model 
stability forecasts and experience suggest this set up can trigger some 
cumulonimbus / thunderstorm development then. 


The second system following Thursday is still forecast in very 
different ways by the European model (ecmwf) and the GFS. The GFS has been consistent 
in forecasting another low to drop along the West Coast Friday and 
park itself off the coast for the weekend. It is expected to also 
pull up moisture and bring another very good chance at precipitation 
over the weekend. The European model (ecmwf) is also consistent in making the next 
one an inside...way inside...slider that closes off a low Saturday 
over the northern Gulf of California. I have leaned towards a 
compromise which the Gem would depict...having the low pinch off 
over Nevada. For now do not have that high a confidence in what will 
transpire and will leave in the relatively high probability of precipitation we have since 
in either solution this looks reasonable. 
&& 


Aviation...for McCarran...light southwest winds will give way to 
light and variable winds along with high level cirrus this morning 
and back to light southwest tonight. Still anticipate a big change 
beginning late Monday and onwards for the rest of the week. By late 
Tuesday through Thursday a system will bring widespread rain to the 
area along with mountain snows. Ceilings are likely to drop near 
or below 5000ft above ground level during this time. Another system is expected 
late Friday to bring another round of widespread precipitation to 
the area for the weekend. 


For the rest of southern Nevada...northwest Arizona...and southeast 
California...light winds and cirrus level clouds expected today and 
into early Monday. Still anticipate a big change beginning late 
Monday and onwards for the rest of the week. By late Tuesday through 
Thursday a system will bring widespread rain to the area along with 
mountain snows. Ceilings are likely to drop near or below 5000ft above ground level 
during this time. Another system is expected late Friday to bring 
another round of widespread precipitation to the area for the 
weekend. 
&& 


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


$$ 


Morgan/Jacques 


Http://weather.Gov/lasvegas