Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 181023

Area Forecast Discussion
National Weather Service Reno NV
323 AM PDT Wed Jul 18 2018


Heat advisories remain in effect through Thursday for western
Nevada. Most areas will be dry through today with only isolated
thunderstorms for southern Mono and Mineral Counties. High
pressure will begin to shift eastward on Thursday with
thunderstorm chances increasing into the weekend as temperatures
gradually cool.



Some modest changes were made to thunderstorm chances for today
and Thursday. Otherwise, the forecast remains on track with Heat
Advisories in effect through Thursday.

Heat continues to build under the upper ridge with today expected
to be the hottest day. High temperatures will increase a couple
of degrees over yesterday this afternoon with Reno forecast to hit
104 degrees. Other western Nevada valley highs are forecast to
reach 100-108 degrees with the highest temperatures occurring in
the sinks of the Basin and Range. Warm overnight lows are also
expected with valleys only cooling down to the 65-75 degree
range. Our advice continues to be to consume extra water if
working or recreating outside today, and know the signs of heat
illness. Temperatures for the Sierra will also be uncomfortable
and possibly an issue for those without air conditioning - highs
in the upper 80s to low 90s and overnight lows around 50 degrees.

Air quality continues to be degraded by smoke from the Ferguson
Fire. Areas of smoke and haze will continue to move into the
region as long as the fire remains active. Conditions may improve
later this week as shower and thunderstorms are forecast which may
aid in removing particulate from the atmosphere.

Thunderstorms were trimmed back this afternoon and tomorrow with
the ridge axis remaining in place longer than previously forecast.
Previous runs favored a more progressive northward movement of the
ridge axis allowing for height falls to aid surface
destabilization to trigger thunderstorms. Now, with the ridge
remaining in its west-to-east orientation for longer,
thunderstorms are less likely today. Additionally, the low that
should develop offshore is moving farther away from the coast
keeping some upper level instability displaced west of the region.
Still, slight chances are possible over higher terrain of
southern Mono and Mineral Counties. Around a 10% chance is
possible as far north as Highway 50 with temperatures over 100
degrees along the Sierra Front. Any thunderstorms that do occur
today will be capable of strong gusty outflow winds.

As for Thursday and Friday, moisture does increase and the ridge
is expected to shift northward. Height falls coupled with hot
surface temperatures and moisture transporting into the region
will support better chances for thunderstorms. These cells will be
wetter as Precipitable Water values climb. Thunderstorms will
still be capable of strong gusty outflow, but will include
localized heavy rainfall as well. Of course, new fire starts
remain possible outside of rain cores as well. Boyd

.LONG TERM...Saturday through Wednesday...

For Sat-Sun the upper ridge remains centered east of our area across
the southern Rockies with a weak ridge axis extending westward
across the Great Basin. Thunderstorms will develop Saturday with
best coverage south of Highway 50. Medium range models show a wave
moving northward into the eastern Sierra and western NV Sunday
although there are some timing issues. The broader scale window
would bring it through sometime from Sat night to late Sunday. So we
could be looking at nocturnal convection and a very active Sunday
across the area, especially south of the ridge axis (general south
of I-80 with lesser coverage farther north). The only change tonight
was to introduce nocturnal thunder Saturday night into Sunday
morning as well as early Monday morning. PWATs are going to be high
and storm motions will be slow. So flash flooding is definitely a
possibility. Temperatures this weekend will be a bit cooler during
the day due to the clouds, but overnight lows will remain on the
warmer side.

For Mon-Wed, most model scenarios continue to retrograde the upper
ridge with it centered over Arizona, far southern NV and southern CA
by Thursday. This would tend to suppress convection although
moisture will still be available to produce enough instability for
isolated to widely scattered thunderstorms (again best potential
near the eastern Sierra south of Hwy 50). The big question will be
how hot it becomes. The GFS shows 700 mb temps rising to 19+C which
would take us right back to 100-105 for lower valleys. The ECMWF is
not quite as hot, but still has us near 100 degrees. We did raise
highs a degree or two to split the difference for now. Hohmann



VFR conditions will prevail for the next couple of days although
areas of haze and smoke aloft from the Ferguson Fire will likely
continue especially near the Sierra. Late afternoon-evening wind
gusts around 20 KT are expected along the US-395 corridor through
Thursday with lighter winds elsewhere. Isolated thunderstorms today
will be confined to the eastern Sierra of Mono county today before
expanding northward to near I-80 Thursday. Storm coverage will
continue to expand northward across most of the region by Friday,
with a potential for heavy rain, reduced visibility, mountain
obscuration and gusty outflow winds. MJD/Hohmann


.REV Watches/Warnings/Advisories...
NV...Heat Advisory until 9 PM PDT Thursday NVZ003-004.

     Heat Advisory from noon today to 9 PM PDT Thursday NVZ005.

     Heat Advisory until 9 PM PDT this evening NVZ001.

CA...Heat Advisory from noon today to 9 PM PDT Thursday CAZ070.



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