Area Forecast Discussion
Issued by NWS Las Vegas, NV

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FXUS65 KVEF 230917

Area Forecast Discussion
National Weather Service Las Vegas NV
217 AM PDT SAT JUL 23 2016

.SYNOPSIS...High pressure will keep hot temperatures in the forecast
for the region through the weekend. Moisture and thunderstorm
chances will begin to return to mainly Mohave and San Bernardino
counties next week.

.SHORT TERM...through Monday night.

Little change in sensible weather for most of the region through the
weekend, with high pressure remaining in control for today and most
of Sunday. Temperatures will run above average, but coverage of
excessive heat criteria is limited, mainly due to this being the
climatological hottest time of the year. During the day on Sunday, a
trough will begin to dig down the west coast from the Pacific
Northwest. This will split the ridge, and allow a component of
southeast flow to develop over southern portions of the area as the
high slides eastward. This will allow modest moisture to return
mainly to southern Mohave county Sunday evening, possibly into San
Bernardino county as well. There is fairly decent consensus among the
models that this moisture will be accompanied by a small
disturbance, so have increased coverage of slight POPs for Mohave
county Sunday and Monday evenings. Temperatures will begin cooling a
degree or two each day as well, although still remaining a few
degrees above normal.

.LONG TERM...Tuesday through Friday. Quite a bit of model spread
this morning leads to below average confidence for this forecast.
The following scenario is believed to be the most likely outcome,
but there are multiple alternatives. Picking up Tuesday morning, the
broad east-west mid level ridge axis remains in place across the
entire lower 48 with a centerline of about 36N. Local concerns
revolve around monsoon moisture and its effect on temperatures. By
Tuesday afternoon, there is at least some agreement on moisture
being present south and east of Las Vegas, so painted slight chance
to low end chance PoPs there. On Wednesday, a trough in the
westerlies dampens the ridge a bit in the eastern states, allowing
heights to rise a few tens of meters as a new high center builds
over the Great Basin. This brings easterly flow to our southern
zones, pushing the moisture and PoPs west into San Bernardino
County, but the big ridge just to the north prevents much northward
progress. Rising heights on Thursday should quash most PoPs. As the
high builds nearby, models agree on ramping temperatures up for
Wednesday and Thursday, but disagree on how much. MEX MOS says
109/111 for KLAS, while ECE MOS says 112/115. Did a roughly 50/50
blend of the previous forecast with the best performing bias
corrected guidance, which gave temps close to the MEX numbers. This
will need to be watched, because if reality ends up closer to the
ECE numbers, Excessive Heat Watches/Warnings will be needed. Another
wrinkle on Thursday is that both the operational GFS and ECMWF show
a tropical system near Cabo San Lucas, which if it verifies, would
push a surge of moisture our way around Saturday. For now, Friday
looks only slightly different from Thursday, with a slowly weakening
ridge suggesting temperatures a degree or two lower and slightly
higher PoPs, still mainly south of Las Vegas.

.FIRE WEATHER...Conditions will be very hot and dry through the
weekend however winds are expected to remain well below any criteria
that would spur a fire weather product issuance.  Chances for
thunderstorm activity will return to the region early next week,
especially across the Mojave desert, lower Colorado River Valley,
and Northwest Arizona.

.AVIATION...Hot and dry conditions expected again today. Winds will
follow diurnal trends with southwest afternoon gusts up to 20 knots
possible later this afternoon.

For the rest of southern Nevada...northwest Arizona...and southeast
California...Dry and hot conditions with winds following diurnal
trends can be expected for most areas. Gusts around 20 knots will be
common in the afternoon hours.

.SPOTTER INFORMATION STATEMENT...Spotter activation is not expected
through the weekend although spotters are encouraged to report any
significant weather using standard operating procedures. Spotter
activation may become more necessary next week.


Short Term/Aviation...Steele
Long Term.............Morgan

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