Freeze Warning 3, NWS Las Vegas, NV

Area Forecast Discussion
National Weather Service Las Vegas NV
947 PM PDT Sat Oct 24 2020

.SYNOPSIS...Drastic weather changes are on the way late Sunday into
Monday. A strong storm system will pass across the Desert Southwest,
bringing strong winds, much colder temperatures, and low chances for
rain and higher elevation snow to area Sunday night into Monday.
Tuesday onward will see quiet weather, with temperatures warming
quickly back up to normal by Wednesday.
&&

.UPDATE...Calm before the storm this evening. Smoke was moving back
into the northern Owens Valley, and all else was quiet. No update
planned this evening.
&&

.AVIATION...For McCarran...South, but occasional southeast winds
overnight with speeds around 10 kts. Winds are expected to gradually
become more southwest Sunday morning, but increase to around 10-20
kt by midday. A wind shift to the north is expected ahead of a cold
front passage tomorrow afternoon. This wind shift could begin as
early as 21-22Z but stronger winds are expected in the late
afternoon as the cold front passes. Winds gusting over 30kts are
possible and cigs could briefly drop to around 10k feet.

For the rest of southern Nevada, northwest Arizona and southeast
California...MVFR visibility will be possible overnight however
smoke will likely clear up tomorrow morning and more so in the
afternoon when winds shift to the north and become gusty due to a
cold front passage. This cold front will also shift all terminals to
the north during the afternoon and evening hours tomorrow. Very low
chance for -RA but if so, should not result in any significant
impacts to the terminals. The cold front is expected to push through
the region during the afternoon with strong northwest to north winds
behind the front. Wind prone areas could see wind gusts approaching
35-40kts.
&&

.PREV DISCUSSION...
249 PM PDT Sat Oct 24 2020

.SHORT TERM...Today through Monday.

The forecast is still on track for rapid and abrupt changes coming
Sunday night into Monday as a trough strengthens as it digs
southward across the Desert Southwest tomorrow. Gusty, southwest
winds will precede this system for the remainder of the today and
early on Sunday before a cold front passes through the area from
north to south shifting winds to the north. These north winds will
become strong Sunday night and Monday with gusts of 40 to 50 mph
possible. Strongest winds look to be down the Colorado River
Valley which will create dangerous waves, up to 4 feet, on Lake
Mead, Mohave, and Havasu. Have went ahead and issued a Wind
Advisory for the river valley and adjacent areas beginning Sunday
evening as confidence is highest in this area seeing consistent
higher gusts above 40 mph. More areas will likely need to be added
in the next forecast packages as confidence increases. Latest
model runs continue to trend drier with a quicker exit to this
system. This leaves precip chances pretty much wrapping up by
Monday morning with most areas outside of Lincoln and Mohave
counties seeing only isolated chances for rain or higher elevation
snow. Even in Lincoln and Mohave counties the precip
accumulations continue to look light, roughly a couple tenths of
an inch at most. The drier trend has also increased fire danger
concerns for Sunday and the Fire Weather Watch has been updated to
begin earlier. The watch time will see periods of increasing RH
values, especially early Monday, but for simplicity sake have gone
with a widespread watch to encompass the drier periods before the
significantly drier air moves in on Monday. There was little
change for the minimum temps Monday and Tuesday mornings and the
Freeze Watch for the Owens Valley has been upgraded to a Warning
for Monday morning. The Freeze Watch remains in effect for Tuesday
morning for portions of southern Nevada and northwest Arizona.
However, the temps are fairly similar for these areas Monday and
Tuesday morning but the overall weather conditions will be more
favorable for hitting freezing temps Tuesday morning with clear
skies and lighter winds so have not brought the freeze products
for these southern areas earlier to Monday.

.LONG TERM...Tuesday through Friday.

The closed low which brought us our weather changes early on in the
week will exit to the east moving along the U.S./Mexico border
before lifting over the southern Great Plains. Weather conditions
will level out pretty quickly Tuesday and Wednesday as a ridge
builds in allowing for dry conditions and winds to come down but
still remain breezy especially down the Colorado River Valley.
Temps will also rebound 10-15 degrees from Monday to Tuesday and
another 5 to 10 degrees Tuesday to Wednesday. This will leave us
right around seasonal normals for the remainder of the long term
period.
&&

.FIRE WEATHER...
Breezy, southwest winds will be replaced by strong north winds
Sunday afternoon through Monday night. Wind gusts will increase to
35 to 50 mph as a cold front passes through area later on Sunday.
Scattered shower activity along with higher elevation snow will
be possible across portions of the area; Lincoln and Mohave
counties in particular. Strong winds and drier conditions will
lead to elevated fire danger Sunday afternoon through Monday
evening. RH values will hover around 20 percent or less for
periods Sunday and Sunday night before significantly drier air
works in behind this system on Monday.
&&

.AVIATION...For McCarran...Initially light and variable winds will
shift to predominantly southwest and increase with minor gusts in
the 21-23Z time frame. Once the shift happens, this should prevail
through the rest of the evening and overnight period. Gusts of up to
20 kts will subside but sustained winds could stay at or above 8 kts
overnight and through tomorrow morning as well. A wind shift to the
north is expected ahead of a cold front passage tomorrow afternoon.
This wind shift could begin as early as 17-19Z but stronger winds
are expected in the late afternoon.

For the rest of southern Nevada, northwest Arizona and southeast
California...Mild southwest breezes are expected for
KVGT/KHND/KIFP/KEED today with KDAG seeing gusts up to 25 kts by the
late afternoon and staying elevating through the rest of the TAF
period. KBIH will once again see the most impact, due to smoke
causing visibility reductions. MVFR visibility will be again
possible overnight however smoke will likely clear up tomorrow
morning and more so in the afternoon when winds shift to the north
and become gusty due to a cold front passage. This cold front will
also shift all terminals to the north during the afternoon and
evening hours tomorrow. Very low chance for -RA but if so, should
not result in any significant impacts to the terminals.
&&

.SPOTTER INFORMATION STATEMENT...Spotters are encouraged to report
any significant weather or impacts according to standard operating
procedures.
&&

UPDATE...Morgan
AVIATION...Gorelow
SHORT TERM/LONG TERM/FIRE WEATHER...Guillet

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