Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Las Vegas Nevada
933 am PST Wednesday Nov 25 2015
Synopsis...a cold front will push south across the region
today bringing much colder temperatures to the region along with a
few showers to the southern Great Basin. Colder air will stick
around through the Holiday weekend. Occasional periods of showers
are expected in the higher terrain of the southern Great Basin and
the Sierra through Sunday. There is some potential for showers
across other parts of the area on Sunday.
Update...a cold front extended from Lincoln County toward the
Clark/southern Nye border and southwest toward Malibu, California.
The front just passed through desert rock shifting winds to the
northeast. Kesx radar is finally getting lower topped precipitation
into radar beam range and thus we are seeing some light returns.
Desert rock ASOS did report a trace of rain as this band passed
through. The radar is overshooting showers across Lincoln County as
Ely has had similar cloudtops on infrared satellite and reported
moderate snow. So we should see some light accumulations especially
north of Pioche as this band of showers moves on through. I adjusted
the pop grids to account for the latest trends on satellite and
The hrrr seems to really slow the wind shift down with the front in
the Las Vegas Valley. This may be a front that gets a wind shift
much quicker in areas north of Sahara Avenue and south of that sees
a delay for winds to go northwest. Either way observation upstream show
winds tanking in strength behind the front and winds will decrease
in the Las Vegas Valley by this afternoon.
The rest of the forecast looks fine at this time.
issued at 451 am PST Wednesday Nov 25 2015
Short term...through Friday night.
Winds should begin to decrease as a cold front pushes south across
the region today. The main highlight with this feature will be the
significantly colder air (15-20 degrees cooler than yesterday) that
will spread across the region...remaining in place into the Holiday
weekend with the upper level low meandering over the Great Basin.
Rain and mountain snow showers may also accompany the front...but
amounts are expected to remain light. The best chances for showers
will be across Lincoln County today. Focus then turns to overnight
temperatures which will likely fall into the 30's in the Las Vegas
Valley and northeast Clark County the next couple night. A freeze
watch remains in place for theses areas since confidence in
temperatures reaching the freezing mark is low at this time.
Long term...Saturday through Wednesday.
By Saturday morning...a Rex block will be firmly in place across the
region with a middle-large upper level low parked over the southern
Great Basin. This will keep cloudy and cool conditions around
through much of the weekend...with afternoon highs generally running
8-12 degrees below average for late November. However...as discussed
in yesterday afternoons afd...the forecast concern for this period
continues to be whether there will be enough moisture present for
precipitation or not. Operational model guidance and their
associated ensembles generally agree in a secondary shortwave
getting pulled into the main upper low Saturday afternoon - Sunday
morning timeframe. Some timing differences do exist between the 00z
GFS and European model (ecmwf) solutions...with the GFS running about 12-18 hours
quicker in bringing the secondary shortwave across the region. Like
the 12z run...the latest run of the GFS continues to aggressively
emphasize the amount moisture associated with this feature as it
rotates around the base of the low. As a result...decided to favor
the less aggressive European model (ecmwf) solution...which does indicate sufficient
middle-level moisture with this feature. Therefore...continued to
mention slight chance probability of precipitation for the Saturday afternoon-Sunday morning
timeframe...mainly across the southern Great Basin zones. It will be
interesting to see how future model runs evolve with respect to
timing this shortwave and how much moisture will be associated with
There is fairly consistent agreement in another piece of energy
breaking off from the Gulf of Alaska low and developing a kicker low
over the eastern Pacific that will help to break the Rex block
pattern over the region. Unfortunately...that is the extent of model
consensus for the time being...as each operational model handles the
evolution of this feature differently...resulting in a low
confidence forecast. As a result...continued mostly with what was
inherited in the grids for Monday through Wednesday morning...with
the chances of continued below average temperatures looking high for
much of the area.
Aviation...for McCarran...southwest winds with gusts of 20-30 kts
and areas of mechanical turbulence will continue through the rest of
the morning before a cold front moves into the Las Vegas Valley
between 19-21z. This front will turn the winds to the northwest...at
least briefly. Winds may return to a more west to southwest
direction later in the afternoon or early evening as the impact from
the cold front diminishes. Few-scattered clouds at or above 8k feet are expected
through the period. Lighter winds are expected through Thursday.
For the rest of southern Nevada...northwest Arizona...and southeast
California...gusty southwest winds will give way to northwesterly
winds as a cold front pushes through the region today. The front
will diminish in strength as it moves through the Las Vegas Valley.
Expect some weak shower activity near the front as it moves through
the southern Great Basin. Lighter winds are expected across the
region Thursday. Scattered-broken clouds mainly at or above 6-8k feet through the
period...along with mechanical turbulence near the high terrain.
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