Scientific Forecaster Discussion
fxus65 kvef 051702
Area forecast discussion
National Weather Service Las Vegas Nevada
902 am PST Thu Dec 5 2019
Synopsis...areas of dense fog will burn off later this morning
with dry day in store for the region. Increasing high clouds can
be expected today and Friday ahead of the next weather system
which will bring another round of rain and mountain snow mainly to
the Sierra and southern Great Basin. Dry and warmer conditions are
expected next week as ridging builds into the region.
Update...the fog has cleared quite a bit this morning with isolated
areas of patchy dense fog possible through 10am. As a result, we've
allowed the product to expire on time. No changes made to the
forecast as it looks to be in good shape.
Previous discussion... /issues at 256 am PST Thu Dec 5 2019/
Short term...through Friday.
Upper low which brought widespread rain and very high altitude
mountain snowfall Wednesday has shifted into southern Utah this
morning. The focus now turns to lingering low level moisture which
has resulted in pockets of dense fog. GOES fog product indicates
extensive low stratus/fog layer blanketing much of Inyo and San
Bernardino counties, where reports of dense fog in the morongo
basin and along sr62 have been received. Additional dense fog
extends across much of southern Nevada, and even Mountain Springs
in the Spring Mountains has been observing dense fog at times.
Patchy fog is also evident across Mohave County where visibility
reductions have been reported along US-93. Went ahead and issued a
broad dense fog advisory for these areas.
Meanwhile, despite the lingering low level moisture, fog has
failed to form across the Las Vegas Valley and the southern Nevada
I-15 corridor thanks to some elevated breezes overnight. Some
patchy fog may develop yet as winds relax in the early morning,
and i'll continue to monitor but in the meantime i've left these
parts of Clark County out of any fog headlines.
After the fog clears this morning, expect increasing high clouds
as yet another trough takes shape off the West Coast. This trough
will move into our area Friday night into Saturday and will be
discussed further in the following section.
Long term...Saturday through Wednesday.
Another progressive trough will edge into the region Friday night
into the weekend. Unlike the past several systems, this storm will
mainly impact the Sierra and southern Great Basin. Additional
snow accumulations of up to a foot may occur in the Sierra above
8,000 feet, though likely falling over the course of a couple
days. Additional headlines may be needed later today or tomorrow
to account for this. Spillover precipitation into the Owens Valley
or the taboose burn area look fairly light.
By next week, ridging will begin to build across much of the
southwest, allowing for a much deserved break from the active
weather. Dry conditions are expected with temperatures near to
slightly above normal. However, will need to watch for development
of surface inversions which could keep some valleys cooler than
the height pattern would suggest.
Aviation...for McCarran...ceilings should generally remain between 4-6k
feet through the day with fairly high confidence there will be no
fog at the terminal this morning. Southwest winds 7-12 knots should
begin to decrease through the early morning hours then becoming
light through the period. Scattered-broken high clouds will move over the
area today becoming broken-overcast aoa 20k feet tonight.
For the rest of southern Nevada, northwest Arizona and southeast
California...areas of fog with reduced visibility will be the
primary concern through 17z this morning. Otherwise, expect broken-overcast
cloud decks between 2-5k feet through the morning hours. Light and
variable winds with increasing high clouds today that will become
broken-overcast aoa 20k feet.
Spotter information statement...spotters are encouraged to report
dense fog and low visibility this morning.