Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 232101

Area Forecast Discussion
National Weather Service Reno NV
201 PM PDT Sun Jul 23 2017


Areas of haze from the Detwiler Fire could return this week, mainly
near the Sierra. Afternoon thunderstorms are expected each afternoon
through Tuesday or Wednesday for northeast California and western
Nevada. Some storms today will produce little rainfall. Stronger
thunderstorms will be possible on Monday and Tuesday as more
moisture arrives bringing increased potential for heavy rain and
localized flash flooding.



Forecast remains on track for thunderstorms this afternoon and
evening. Storms are already kicking off across central Nevada, so
now we just play the waiting game along the Sierra Front. The
primary concerns with any storms that develop will be for narrow
rain cores, gusty outflow winds, and lightning that may produce new
fire starts. Red flag warning is still in effect for much of the
afternoon and evening for the Sierra and western Nevada. For more
details about fire weather concerns see the Fire Weather discussion.

Over the next few days the Sierra and western Nevada will remain in
a very favorable thunderstorm pattern with an upper low just off the
coast producing divergent flow and an unstable mid-level atmosphere
over northern California and Nevada out ahead of the low. As the
upper low approaches, moist southerly flow along with steep upper-
level lapse rates will allow for increased thunderstorm potential.
Storm motions between 10-20 mph this afternoon and evening along
with elevated bases and small rain cores will limit rainfall amounts
with storms today, but cannot rule out some localized heavier
showers, especially along the Sierra.

Thunderstorm threat will gradually increase each day as the upper
slowly moves across northern California. Continued divergent flow
aloft over northern California and western Nevada may result in
nocturnal convection (showers and/or thunderstorms) tonight and
Monday night. The instability aloft may only result in just mid-
level clouds; however, a low chance for showers and thunderstorms
is warranted.

By Monday and Tuesday afternoons, model soundings show increasing
flow aloft along with sufficient instability (~1000 J/kg) which
could support the development of stronger, more organized
thunderstorms. Also, with precipitable water values flirting near
the 1" mark each of those days, the threat for heavy rain and flash
flooding also increases. While we could get localized heavy rain on
any of these afternoons, including today, the better potential for
those heavy rains will be by Monday and Tuesday afternoons. It is
also important to note that there might not be much of a break from
Monday night going into Tuesday. Some simulations show showers and
thunderstorms continuing overnight. Please have multiple ways to
receive alerts for flash flooding, especially if you live in a flood
prone area (steep terrain, burn area, or near a wash). The upper
level jet associated with the low will be right over the region on
Tuesday, which could also allow for some severe storms to develop.

Finally, as the low moves out of the region on Wednesday the flow
aloft turns more southwesterly allowing for drying conditions and
less potential for thunderstorms, especially north of Interstate 80.
Residual moisture appears to hold on south of the I80 corridor with
low chances for thunderstorms hanging around for Mono, Mineral, and
Alpine counties. -Edan

Four Corners ridge remains in place through the end of the week and
into next weekend. Although a warming trend returns with
temperatures rising to above normal again, the main concern will be
the position of the ridge through the weekend into early next week.
For now the forecast is edged towards the warmer and drier outcome,
but that can change as the location of the ridge will be the main
determine factor. If the ridge axis remains centered over the
Four Corners region, then southerly flow would allow for monsoonal
moisture to move up into the region. -Edan


Thunderstorm chances increase today through Tuesday with scattered
showers and thunderstorms each afternoon and evening. While the
chances are lower than during the day, it is worth mentioning that
nocturnal storms will be possible both tonight and Monday nights for
much of the area as well. Main threats will include lightning, gusty
outflow winds, small hail and localized heavy rainfall.
Thunderstorms will initiate over the higher mountains and Sierra,
then move north and east into the western Nevada Sierra Front. 20-
30% chance of thunderstorms are expected for all area terminals this
afternoon and evening. Thunderstorm chances will continue for Monday
and Tuesday, but threats will transition to heavy rain and increased
potential for flash flooding. Hoon/Edan



Thunderstorms are beginning to fire over Mineral County this
afternoon with buildups now along the Eastern Sierra foothills from
Mono County up to Doyle. Expect more storms to fire and with the
very dry low levels, the storms will be initially dry with the
potential for starts. The storms will become wetter as the evening
rolls on. At this point, it appears the Tahoe Basin will see the
lowest threat of any storms. The best coverage looks to be zones
459/453/458/278/271 from southeast to northwest given current trends
and model output.

After this evening, a few thunderstorms will remain possible as
there are a couple weak waves moving through into Monday morning. In
addition, more moisture will arrive with a better chance for
thunderstorms Monday along with wetting rains. Expect scattered wet
thunderstorms for almost all areas Monday afternoon and evening.
Outflows could still be strong at 40-50 mph and push any active
fires about.

More of the same Tuesday as the upper low pulls through with mainly
wet thunderstorms expected. Also, RH will be considerably higher due
to cooler temperatures and the increased moisture.

Drying Wednesday with RH returning to seasonably low values and
only fair recovery late in the week. Temperatures will also warm
for next weekend with hot temperatures expected and poor RH
recovery likely for many mid slopes. Thunderstorms will return at
some point, but when and how wet are unknowns. Wallmann


.REV Watches/Warnings/Advisories...
NV...Red Flag Warning until midnight PDT tonight NVZ450-453-458.

     Red Flag Warning until 9 PM PDT this evening NVZ459.

CA...Red Flag Warning until midnight PDT tonight CAZ270>272-278.

     Red Flag Warning until 9 PM PDT this evening CAZ273.



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