Scientific Forecaster Discussion
fxus65 kvef 211207
Area forecast discussion
National Weather Service Las Vegas Nevada
405 am PST Wed Nov 21 2018
Synopsis...an incoming Pacific low pressure system will bring
snow to the southern Sierra tonight and a chance for brief isolated
to scattered showers over much of the region on Thanksgiving day.
Dry conditions will return Friday, but north winds will increase
Saturday...especially along the Colorado River valley. Slightly
cooler temperatures can be expected Sunday.
Short term...through Thursday night
A Pacific low pressure system is still on track to bring a change in
the weather to our region tonight and Thanksgiving day. Impacts, if
any, will be minor outside of the Sierra which will intercept most
of the moisture. The leading edge of the system was making its way
into central and northern California early this morning and the
latest models indicate any snow spilling over the east slopes of the
southern Sierra will hold off until this evening, with a 9-12 hour
window of snowfall probably peaking between 10 PM and 4 am. The
Winter Storm Watch was replaced with a Winter Weather Advisory for
the east slopes with generally 3-7 inches of accumulation expected
at elevations between 7000 and 9000 feet and higher amounts near the
crest. The GFS and ECMWF indicate a fairly narrow moisture plume
sliding under the Sierra and spreading across northern San
Bernardino County into the Spring Mountains early Thursday morning.
This may drop an inch or two of snow around Mount Charleston and Lee
Canyon before the system quickly races away to the east before noon.
Isolated to scattered showers will leave light precipitation amounts
across the rest of southern Nevada and northwest Arizona and the
back side of the showers will have moved away into southern Utah and
north central Arizona by late afternoon leaving dry and fairly
tranquil conditions Thursday night except for some gusty west winds
over the San Bernardino County deserts. Temperatures will not
fluctuate much during the period.
Long term...Friday through Wednesday
A moist northwest flow will slam into northern California on Friday.
While most of this moisture will be mainly north of the forecast
area, portions of the southern Sierra will see more snow
accumulation through Saturday morning. Portions of northern Lincoln
County will also have a chance at a band of showers as an inside-
slider moves southeastward from the pacnw into northern Utah on
Saturday. Elsewhere, dry conditions are expected. Dry conditions are
expected after the system ejects eastward Saturday afternoon and
should remain dry through the remainder of the period. Rain/snow
chances will creep back into the forecast next week as broad
longwave trough sets up across the western two-thirds of the Continental U.S..
This same system will also bring more wind with it. The southern
Sierra will see downslope enhancement winds Friday as the trough
moves south. Strongest winds look to be in the neighborhood of 25-35
miles per hour with gusts approaching 50 miles per hour and should only extend to the mid-
slopes of the Sierra. Along with prefrontal downslope, an along and
Post-frontal north wind will slide across the southern Great Basin
Saturday with winds 15-25 miles per hour and gusts up to 35 miles per hour. North winds
will linger down the Colorado River for a couple days after the
frontal passage (as they typically do!).
Aviation...for McCarran...light winds generally under 6 knots
favoring typical diurnal trends are expected today and this evening.
Southwest winds will increase late tonight and early Thursday
morning with gusts of 20-25 knots possible along with a brief
periods of scattered-broken clouds around 8 kft and showers near the Spring
For the rest of southern Nevada, northwest Arizona and southeast
California...a Pacific low pressure system will move across the
southern Sierra tonight and the rest of the region Thursday. This
will bring snow and mountain obscuration to the southern Sierra
tonight and increasing winds and potential turbulence in the Lee of
the Sierra and high mountains around the region. Scattered showers
will develop early Thursday morning across the southern Great Basin
and Mojave Desert region with cloud bases of 6-8 kft mean sea level
creating mountain obscuration with snow levels around 6-7 kft mean sea level.
Spotter information statement...spotters are encouraged to report
any significant weather or impacts according to Standard operating