Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Las Vegas Nevada
838 PM PST Tuesday Nov 24 2015
Synopsis...gusty southwest to west winds will continue overnight
ahead of a cold front that will press across the area on Wednesday.
A few showers will also accompany this front mainly over the
southern Great Basin. Much colder air will arrive in the area for
Wednesday and last through the Thanksgiving Holiday weekend. Periods
of clouds are possible through the weekend along with isolated light
showers mainly in the southern Sierra Thanksgiving day and Friday
and over the higher elevations on Saturday and Sunday.
Update...just made a few changes to the sky forecast through
tonight to account for a broad area of middle-high clouds moving across
the southern half of the County Warning Area. Otherwise the forecast outlined below
is panning out as expected with gusty winds across most of the
350 PM PST Tuesday Nov 24 2015
Short term...tonight through Friday night.
Winds picked up and mixed out the inversion nicely pushing Las Vegas
up to 75 for a high today at McCarran. This could very well be the
last time this year we see anything this mild as at least for the
next week we will be much, much colder. Currently water vapor shows
the center of the middle and upper level over southwest Oregon. This
low is expected to head southeast toward northeast California
tonight and toward north-central Nevada on Wednesday. There is not
much in the way of moisture well ahead of this system (especially in
the middle and lower levels) and thus an substantial increase in clouds
and shot at precipitation will come this evening into later tonight.
There appears to be a band of showers that develops along the
surface cold front that will work across the area tonight and become
better organized as it moves from central Nye County into Lincoln
and northern Clark counties thanks to frontogenesis. So, probability of precipitation were
bumped up in this area even more. We should be able to squeeze out
some light accumulating snow even on Mount Charleston later tonight
into Wednesday morning and perhaps could even see some sprinkles or
a light shower in Red Rock Canyon and on the far west side of the
Las Vegas Valley. Any showers will not last long outside of Lincoln
County as the front shifts to the east. Snow levels across Lincoln
County should drop to 3500-4000 feet which could bring up to 2
inches of snow with it. The highest snow totals would be along the
crest and in the upper eastern slopes of the southern Sierra where 2
to 4 inches of snow is possible this evening into tonight.
A Wind Advisory was added for the Owens Valley as winds at a few
mesonet sites have gusted over 40 miles per hour. However, it appears these
stronger winds will remain confined to downwind of more favorable
canyon openings. The remaining wind headlines look good as winds
will peak this evening into the early morning hours as the core of a
110 kt+ jet stream moves south over the area providing good
momentum. Winds will remain gusty tomorrow morning across the
southern tier of the area (san Bernardino/Mohave counties) as the
jet will be exiting these areas later on.
High temperatures will be 12-20 degrees colder on Wednesday than today and
remain so through Friday. Energy wrapping around the slowly
departing low and lingering middle-level moisture will still keep a
decent amount of clouds around at times across the area from I-15 on
north through Friday. It will be close tomorrow night for the first
freeze of the season in outlying parts of the Las Vegas Valley and
in northeast Clark County spots like Mesquite and if it does not
happen then it will on Friday morning. A freeze watch was posted for
then. The most likely spots in the Las Vegas Valley either night to
see a freeze will be in areas less prone to northwest winds on the
south end and out near Nellis AFB. With the wrap around energy and
moisture, we may see some light showers develop mainly over the
southern Sierra on Thanksgiving day and Friday. Elsewhere it should
stay dry but overall cold Turkey is the flavor of this forecast.
Long term...Saturday through Tuesday.
An upper low that has been nearly stationary for several days will
remain parked over northern Nevada for as least the first half of
the extended period. This will keep temperatures rather cool through
the period with readings generally 10-12 degrees below normal. Winds
are not expected to be much of a factor as surface gradients will
remain fairly relaxed. The real concern for the extended period will
be the potential for precipitation over the weekend. This is where
the models show some major differences. The European model (ecmwf)/GFS/dgex all grab
onto a piece of energy over the eastern Pacific and eventually begin
pulling it toward Southern California on Saturday around the upper
low. The European model (ecmwf) weakens this feature as it moves closer to the coast
and eventually weakens it enough that all that remains are just a
few clouds that move across the region late Saturday and Sunday. The
GFS and to some extent the dgex pull that energy onshore along with
a decent amount of moisture that eventually moves across the County Warning Area
Saturday night and Sunday. Would tend to lean a bit more toward the
GFS with regards to higher moisture amounts and a little better
shower chances. Did go ahead and increase probability of precipitation slightly for the
Saturday/Sunday timeframe...but only into the slight chance/chance
By Monday the pesky upper low is expected to finally get shoved east
by another system that will approach the West Coast. In between
systems will be a weak upper ridge that will bring generally clear
skies and light winds...but still keeping temperatures rather cool
with only a slight warming trend by Monday and Tuesday.
Aviation...for McCarran...gusty southwest winds expected to
continue across the terminal through at least middle day Wednesday.
Speeds expected to be around 15-25kts with occasional gusts near
30kts. Cold front will move through around middle day Wednesday with
winds shifting to the northwest with speeds generally around 8-
15kts. Few-scattered clouds around 15-20k feet. A few showers will be
possible near the front over the Spring Mountains and Sheep Range
with the possibility of the higher peaks obscured Wednesday.
For the rest of southern Nevada...northwest Arizona...and southeast
California...gusty south to southwest winds are expected to continue
overnight ahead of a cold front that will move through the region
Wednesday. Winds ahead of the front will generally be 15-30kts with
the strongest winds over much of Inyo County...central and southern
Nye...and western Clark County. Strong downslope winds are also
expected in the Lee of the Sierra and Spring Mountains overnight.
Winds behind the cold front will decrease with speeds between 10-
20kts. There may be a few showers along the front with the greatest
chance across central Nye and Lincoln counties.
Spotter information statement...spotters are encouraged to report
any significant weather conditions according to Standard operating
procedures Tuesday and Wednesday.
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