Area Forecast Discussion
Issued by NWS Las Vegas, NV

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FXUS65 KVEF 250331
AFDVEF

Area Forecast Discussion
National Weather Service Las Vegas NV
831 PM PDT Mon Jul 24 2017

.SYNOPSIS...A significant push of monsoon moisture will spread
northward today bring the threat of heavy rain and thunderstorms to
much of the area over the next couple of days. The greatest threat
will occur today and Tuesday afternoon before a drying trend begins
mid to late week. &&

.UPDATE...Updated near term POP/QPF/Wx grids to reflect current
trends. Otherwise forecast seems to be on track, and no other
updates were made this evening. -Kryston
&&

.AVIATION...For McCarran...Showers and thunderstorms still possible
overnight tonight and into the early morning hours. Outside of
thunderstorm chances, a southwest to south wind between 10-15 kts
will persist through the evening hours with light and variable winds
setting up between 10z-12z. Thunderstorm chances will remain between
30-40 percent through Tuesday afternoon and evening, however,
thunderstorm chances are forecast to trend downward through the rest
of the week. Cigs above 10 kft prevailing but could drop to 7 kft
with storm over the terminal.


For the rest of southern Nevada, northwest Arizona and southeast
California...Scattered showers and thunderstorms are expected to
impact much of the region through Tuesday with potentially heavy
rainfall. Cigs will generally be around 10-12k feet, but could fall
to as low as 5k feet in heavier storms. Winds will generally be from
the south to southeast at 10-15 knots with gusts to 20 knots, but
more gusty and erratic near any storms.

&&

.PREV DISCUSSION... /issued at 100 PM PDT Mon Jul 24 2017/

.SHORT TERM...Today through Wednesday

Heavy thunderstorms have developed this afternoon concentrated along
the Spring Mountains west of Las Vegas. Some of these storms have
produced rainfall rates over 2 inches per hour, and additional
thunderstorm development is likely though the afternoon.
Meanwhile...vorticity maxima moving northwest from central Arizona
will arrive in our forecast area this evening to be located near
Lake Mead around 5 pm. This will serve as an additional mechanism
of upward motion and a focus for additional thunderstorm
development. This disturbance will continue northward tonight and
scattered to numerous thunderstorms are likely to persist across
Lincoln, Northern Mohave and Clark counties.  Given the extremely
moisture rich airmass, thunderstorms will be possible both day and
night, and it wont take much to trigger thunderstorm activity even
during the very early morning hours.  Several convective allowing
models are suggesting an uptick in convective activity early Tuesday
morning across the I-15 corridor from Las Vegas to St George...and
given the very anomalous moisture in place as well as slow storm
motion....decided to extend the Flash Flood Watch for those areas
through Tuesday evening to account for potential flood impacts
tomorrow morning and afternoon. Have left San Bern and southern
Mohave counties out of the watch extension at this time.

On Wednesday....things will tend to dry out as a weak southwest flow
gradually dries out the mid and upper levels of the atmosphere. Low
level moisture will remain above normal however and scattered
afternoon and evening storms will remain a possibility for much of
the region, but coverage and intensity will trend less.

Temperatures today and tomorrow will struggle to beat triple digits
in areas where rain and clouds are abundant, but will return closer
to normal on Wednesday. Further West, across Inyo and Western San
Bern counties, near to slightly above normal temperatures can be
expected each day.

.LONG TERM...Thursday through Saturday.

Gradual drying and warming is expected for Thursday as weak
southwest flow returns to the region. Enough moisture is likely to
remain in place for afternoon showers/storms over favored high
terrain.

By Friday, high pressure once again pushes back to a favorable
location near the Four Corners, allowing for a moist southeasterly
flow into the region. However, this is where guidance begins to
diverge, with the GFS keeping the high and favorable flow well into
the weekend while the ECMWF is significantly different, pushing the
high to near Reno and keeping much of the moisture to the south of
Las Vegas. For now I`ve split the difference, increasing dew points,
and  PoPs over the area, but with a emphasis on areas south of Las
Vegas.
&&

.FIRE WEATHER...Scattered showers and thunderstorms will occur over
much of the region today with any storm capable of producing very
heavy rainfall. Although storms will be possible in Inyo County
today, those are expected to be more isolated. However, areas of far
southeastern Inyo could see more scattered storms. Conditions will
gradually dry out midweek onward, with thunderstorms decreasing in
coverage each day. Temperatures will be near normal to somewhat
below normal through Wednesday, before returning to slightly above
normal late in the week.
&&

.HYDROLOGY...
Creeks, streams and rivers in northern Inyo County have shown
decreasing flows over the last couple of days. However, some road
closures continue in the area. Bishop Creek Bypass and Big Pine
Creek Bypass continue to be utilized to minimize flows through
Bishop and Big Pine. Remember, never drive through flooded
roadways or around barricades. Also, pastureland or farmland
adjacent to creeks, streams or rivers could experience areas of
standing water.
&&


.SPOTTER INFORMATION STATEMENT...Spotters are encouraged to report
any significant weather and especially flood impacts the next
several days as an active monsoon pattern unfolds.

&&

$$

Short Term...Outler
Fire Weather...Gorelow
Aviation...Boothe
Long Term...Wolcott


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