Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 250309
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
809 PM PDT Sat Jun 24 2017

.UPDATE...
Isolated storms formed on our side of the Sierra Crest from Mono
County to just south of Tahoe. Other storms fired just west of the
crest from Sierra City to Lassen Park. Overall the storms have
diminished, but a few showers remain west of the crest south of
highway 50. Expect an overall quiet night, but the wave mentioned
earlier, there will likely be some accas after sunrise north of
Tahoe. The wave and upper level lapse rates over 7.5 C/km would
support this. It doesn`t appear strong enough for any decent
convection, but an isolated strike or two during the morning hours
is not out of the question. This is handled well overall by the
previous forecast so no updates are anticipated at this time.

&&

.PREVIOUS DISCUSSION... /Issued 143 PM PDT Sat Jun 24 2017/

SYNOPSIS...

Well above average temperatures continue through the weekend with
some cooling by early next week. Isolated thunderstorms are
possible near the Sierra this evening, spreading into parts of
western Nevada and northeast California Sunday. Critical fire
weather conditions are possible Monday as very dry air combines
with gusty winds. After a brief cool down to near normal
temperatures, a building ridge will bring another round of well
above normal temperatures to the region starting Friday. Flooding
will continue for the creeks in Mono County and portions of the
Walker River.

DISCUSSION...

Isolated convection is possible into the early evening hours along
the Sierra from Mono County north to around El Dorado County. The
latest HRRR guidance is less robust of the east side of the
Sierra...keeping much of the activity west of the crest. But the
HRRR does hold out some slight chances for the Alpine County area.
For the time being we will not reduce thunderstorm coverage...but
we be a little over done.

Attention turns to a mid level short wave lifting northeast across
the region Sunday. Models have been trending down in terms in
thunderstorm coverage with this feature. Timing is critical as a
morning passage would tend toward less coverage overall. Right
now it appears the best chance for increased coverage will be
north of I-80 and west of a line from Cedarville to Gerlach. A
potential vorticity maximum will be lifting across northeast
California by late afternoon...but this appears to be the only
mid/upper level support. Lapse rates aloft are not impressive and
there is little in the way of jet support. While the convection
should be rooted in a deep...well mixed boundary layer...the lack
of upper level support will limit organization and coverage.
Still...with increasing instability it is not out of the realm of
possibility that we will see early development and continual
cycling of storms from late morning into the afternoon. Any storms
that develop would be moving fast enough to limit precipitation
potential and produce dry lightning strikes. Showers linger into
late Sunday night and early Monday morning over the far north.

Drier air moves into the region and breezy winds develop Monday
and Tuesday. Monday looks like the day with the best potential for
critical fire weather conditions. See the Fire Weather discussion
for more details. In the wake of the short wave trough...heights
fall and temperatures Monday and Tuesday will drop back to just
slightly above normal. This will slow snowmelt a bit in the
higher elevations.

Another trough will slide toward the region from the northwest
Wednesday. This trough should bring mainly an increase in clouds
as low level moisture is lacking for showers. Northwest flow aloft
and low northeast develops in its wake Thursday.

By Friday a ridge starts to build back into the region. This will
bring a return to well above normal temperatures and possibly
enough instability for isolated convection along the Sierra. For
now we will leave mention of thunderstorms out of the forecast for
Friday and Saturday...but they may need to be added in a few days.

AVIATION...

Isolated storms along the Sierra should be the only aviation
concern for the first 12 hours of the forecast. A mid level trough
of low pressure lifting northeast across the region Sunday will
bring an increase in coverage for storms. The best chance for
storms is across northeast California and far western Nevada...but
we could see isolated storms all along the Sierra.

As the trough lifts out late Sunday night a few showers will
linger north of Susanville. Then...breezy winds will develop for
Monday with surface gusts approaching 30-35 kts in many locations.
Breezy continues continue into Tuesday...but the gusts will be a
little less than Monday.

FIRE WEATHER...

Temperatures have warmed into the upper 90s with low 100s still
likely for the daily high for many locations in western Nevada
today. Recoveries were moderate to good in the Sierra last night
with poor to moderate for western Nevada. With temperatures running
warmer today, expect slightly poorer recoveries overnight into
Sunday which will heat back to the upper 90s to low 100s again.

Meanwhile, towering cumulus and a few thunderstorms have formed in
the Sierra and along the Long Valley Caldera rim in southern Mono
County. Expect thunderstorms to continue to form along outflow
boundaries and higher terrain of the Sierra mainly south of the
Tahoe Basin through the rest of the afternoon. Gusts in valleys
could be strong with slight potential for a stray dry lightning
strike.

Main changes to the ongoing forecast have been to trim thunderstorm
chances down slightly for Sunday as models continue to show an
earlier passage of a destabilizing upper wave. With this wave
passing earlier Sunday morning, instability aloft will be un-
phased from highest surface instability. Still, chances of
isolated thunderstorms cover a much larger area than recent
activity. Any storms that form will be capable of producing strong
gusts and dry lightning strikes, especially if they move over
western Nevada valley locations. Just a few strikes along the
Sierra Front would likely be enough to allow for new fire starts
since dried grasses are nearly continuous.

Finally, an upper low moves into northern California Monday increasing
winds across the region. Expect critical fire weather conditions
for western Nevada as winds gust around 35mph. As such, a fire
weather watch remains in effect for portions of western Nevada
including the Sierra Front, northern Lyon County, and
Churchill/Pershing Counties. Winds drop off below critical
thresholds Tuesday and Wednesday, but would still be able to drive
any grass fires that may occur.

Grasses east of Highway 395 in California, mainly in Lassen County,
have mostly cured and could propagate fire. While this zone is not
technically fire ready, it`s something to prepare for. It should
also be noted that sagebrush in western Nevada valleys is beginning
to show signs that it is becoming dry enough to carry fire; it may
not contribute to explosive fire growth, but it will be available to
burn. Boyd

&&

.REV Watches/Warnings/Advisories...
NV...Fire Weather Watch from Monday afternoon through Monday evening
     NVZ450-453.

CA...None.
&&

$$

For more information from the National Weather Service visit...
http://weather.gov/reno


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