884
FXUS65 KVEF 191805
AFDVEF

Area Forecast Discussion
National Weather Service Las Vegas NV
1105 AM PDT Fri Jul 19 2024

.SYNOPSIS...Isolated to scattered thunderstorm chances
continue this afternoon across southern Nevada, northwest Arizona,
and northern Inyo County. This weekend, rain chances become
primarily confined to Mohave County and the southern Great Basin as
excessive heat builds across the Mojave Desert. Storm chances expand
west next week as moisture increases once again.
&&


.UPDATE...Another round of convection expected today across
northwestern Arizona and southern Nevada favoring the higher
terrain. Largest impacts will be localized flash flooding in Mohave
County, with strong gusty winds in southern Nevada due to dry air at
the surface. Time frame will be similar as yesterday, with storms
popping up within the next hour and lasting through around sunset.
That said, we are expecting less storm coverage than yesterday.

Excessive Heat Warning went into effect this morning at 10am PDT for
our southern zones including southern San Bernardino County,
southern Mohave County, and the Colorado River Valley. This warning
will expand to include southern Nevada and parts of southeastern
California through Sunday. No changes made to the forecast this
morning as it looks to be in good shape.
&&


.PREVIOUS DISCUSSION...159 AM PDT Fri Jul 19 2024/

.DISCUSSION...through next Friday.

The 500mb high continues to slowly drift westward, progressing into
western/central AZ tomorrow and practically overhead this weekend.
As this occurs, 850mb flow actually becomes more westerly, leading
to decreased moisture advection up the Colorado River Valley. This
results in a slight decrease in moisture across the Mojave Desert
over the next three days. PoPs this afternoon are highest in Lincoln
and eastern Mohave counties, though 20-40% chances still exist in
parts of Clark County and our northwestern areas, primarily on the
high terrain. Main concerns with any convection will be isolated
flash flooding and gusty outflow winds. This weekend, when the high
moves overhead, PoPs become more confined to Lincoln and Mohave
counties.

The other impact of the 500mb high moving into our area is the
increasing heat. Temperatures gradually creep up through the
weekend, with Major and Extreme HeatRisk spreading west/north. An
Excessive Heat Warning goes into effect at 10 AM this morning for
the Colorado River Valley and southern Mohave/San Bernardino
Counties. On Saturday, the warning expands to include the remainder
of our San Bernardino zones, the lower elevations of Clark County,
southern Nye County, and Death Valley. The Excessive Heat Warning
runs through Sunday evening.

Next week, the upper-level high drifts ever so slightly northwest
and at least some moisture advection resumes as 850mb flow in the
Colorado River Valley acquires a southerly component. This lets
better moisture return to the Mojave Desert, with 1" PWAT
probabilities along the I-15 corridor increasing from 30-60% on
Monday to 60-90% on Wednesday. The increase in moisture allows PoPs
to increase and spread westward. Latest NBM has rain chances
increasing to 20+ percent across the majority of the CWA by Tuesday
and Wednesday. Suspect these values are at least somewhat inflated
by NBM climatology, so brought them down slightly in the forecast,
but didn`t make too many cuts given the moisture return shown in
ensemble guidance. The potential for scattered convection will also
influence the temperature forecast next week. Temperatures are
likely to remain above normal, but whether they are able to keep
HeatRisk at Major/Extreme levels remains to be seen. Given the
uncertainty, any changes to the current heat headlines will have to
wait until convective coverage early next week becomes clearer.

Late in the work week, ensemble guidance is in fairly good agreement
that a trough moving into the PacNW will flatten the ridge. This
would result in cooler and drier conditions across the area.
&&


.AVIATION...For Harry Reid...Partly cloudy skies along with light
winds this morning. Showers and thunderstorms will start to develop
on the Spring Mountains and McCullough Range west and south of the
valley between 18Z and 20Z. Additional storm development will occur
within the valley between 20Z and 24Z associated with gusty outflow
winds predominately from a south or southeast direction, but could
ultimately come from any direction. Shower and thunderstorm chances
diminish after sunset, with winds returning to typical diurnal
direction through the evening and overnight hours. Less shower and
thunderstorm threat on Saturday (<10%) as any storms will weaken as
they move into the valley.

For the rest of southern Nevada, northwest Arizona and southeast
California...Best coverage for thunderstorms today will be in
southern Nevada, northwest Arizona and the southern Sierra Nevada of
Inyo County. Primary hazard with these storms will be gusty outflow
winds up to 40 mph. Restricted visibility due to locally heavy rain
is possible as well. Slight decrease in coverage of storms Saturday,
primarily favoring east central Nevada and northwest Arizona. Main
concerns again being erratic, gusty surface winds and locally heavy
rain.
&&


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

&&

$$

UPDATE...Soulat
DISCUSSION...Woods
AVIATION...Pierce

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