Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 190523 AAA
AFDREV

Area Forecast Discussion...UPDATED
National Weather Service Reno NV
1023 PM PDT Sun Jun 18 2017

.UPDATE...short term and hydrology

Thunderstorms fired along the eastern Sierra earlier this
afternoon/evening with a few very strong cells capable of heavy
rain and small hail. Storms have since decreased but models keep
some convection around overnight as shortwave noted in satellite
data works northward around upper ridge. Temperatures were running
quite a bit warmer this evening due to the extensive cloud cover.
As clouds break, temperatures should have no problem pushing to
near 100 degrees Monday before convection fires. Models are still
showing thunderstorms developing along the crest midday/early
afternoon and then pushing off into western NV during the mid to
late afternoon Monday. Both the GFS/NAM are now showing a notable
outflow signature across west central NV which may suggest more
organized convection developing along the Sierra Front in
conjunction with the afternoon zephyr and potential for strong
winds.

As far as the Walker River, streams continue to perform at or
higher than forecast and the higher elevation snowpack is really
beginning to respond. With the very warm temperatures expected to
persist, these trends are likely to continue. The only
uncertainty will be reservoir releases and how fast the reservoirs
fill. Minor flooding is already occurring and with additional
inflows into the Walker River system, moderate flooding is
becoming a real possibility. We have issued a flood warning for
the Walker River from Mason to Weber Reservoir for the balance of
this week and possibly beyond. Hohmann

&&

.SYNOPSIS...
High pressure will bring much above average temperatures this
week with records possible through Wednesday. The threat for
thunderstorms will increase into Monday and Tuesday and then
decrease again for the rest of the week. Snowmelt runoff will
increase flows especially on creeks and streams flowing out of
Mono County.

&&

.PREVIOUS DISCUSSION... /Issued 222 PM PDT Sun Jun 18 2017/

SYNOPSIS...
High pressure will bring much above average temperatures into next
week with records possible through Wednesday. The threat for
thunderstorms will increase into Monday and Tuesday. Isolated
storms are possible in the Sierra this afternoon with storms
spreading north to the Oregon border and western Nevada by
Monday. Snowmelt runoff will increase flows especially in the
Walker River basin and creeks in Mono County.

DISCUSSION...
Not much has changed in overall forecast philosophy the last 24
hours. The anomalous near record heat will continue and we still
expect a few thunderstorms this evening over Mono County with the
best threat of thunderstorms Monday. By midweek a drying trend is
expected, but the cooling for late in the week looks modest at
best. Record highs remain possible Monday through Wednesday with
cooler, but still above average temperatures into next weekend.

Plenty of moisture remains across the region with precip water of
3/4 inch or more, but the limiting factor for thunderstorms
continues to be the warm temps aloft. If storms form over Mono
County this evening, they will be isolated in nature, slow moving
and produce brief heavy rains. Still, given the stability I would
not be surprised if nothing formed other than some buildups.

Monday is looking much more likely for convection with slightly
cooler temps aloft and surface temps warming. The moisture in
place will remain as low level flow remains very light. Expect
most areas to see isolated convection with some increase in
coverage from Mono County through the Sierra Front. The idea is
that a weak zephyr will form (or outflow from earlier Sierra
convection) and set up a boundary for more organized and
widespread convection. The biggest threats will be brief heavy
rains and gusty winds. While the storms are expected to be wet,
there are still fire weather concerns, see the Fire Weather
segment below.

Tuesday the flow becomes more southwest aloft which will begin to
scour out the moisture. Isolated storms remain possible south of
I-80 and also downstream of Lassen Peak in WSW flow aloft.
Wednesday looks to be mostly dry, but there is a weakness in the
ridge which is forecast to drop just west of Mono County. Added
the threat of thunderstorms for Mono and western Mineral counties
Wednesday.

The upper high finally retreats south late in the week as low
pressure moves into the Pacific Northwest. However, these waves
will remain well north and only flatten the ridge a bit. The GFS
is now in good agreement with the EC in keeping a stronger ridge.
Highs into the 90s are still expected in Western NV and 80s in
the Sierra into next weekend. Winds will remain somewhat light
aloft with a SW component, while at the surface prevailing winds
from the north to east are anticipated. These surface winds could
shift to a weak zephyr by late afternoon as the temps in the
Sacramento Valley cool, but it remains hot in West Central Nevada.
Wallmann

AVIATION...
Mainly VFR into Monday with light winds. The main threat is
thunderstorms which will be isolated near KMMH this evening, but
potentially affect all terminals Monday. The biggest threat from
the storms will be gusty outflow winds to 40 kts along with
lightning, brief heavy rain and small hail.

Fewer thunderstorms Tuesday, but a return to more typical
afternoon W-SW winds with gusts 20-25 kts. Wallmann

FIRE WEATHER...

We will continue to include a headline for the increased
thunderstorm threat Monday afternoon in the Fire Weather Forecast.
The very warm temperatures will continue to dry out grassy and
finer brush fuels during the next several days across western NV. By
Monday, potential for thunderstorms increases near the Sierra, and
across portions of western NV mainly from the Sierra Front
eastward to near a Fernley-Hawthorne line. A secondary area
with an increased thunderstorm threat includes far northwest NV and
the Surprise Valley. Projected surface dew points in the 40s with PW
values at least 0.80 inch and slow cell movement will favor wet
thunderstorms. A few lightning-induced fire starts are possible, but
with this amount of moisture the fuels may be less receptive to
ignition, and rain associated with these storms will have a good
chance of ending any fires that might start.

For Tuesday, the thunderstorm threat shifts a bit farther east away
from the Reno-Tahoe areas, but continues across west central NV
southward to Mono County, and also across far northeast CA and
northwest NV. Moisture isn`t expected to be as substantial (PW
values drop to near 0.60 inch with surface dew points dipping to the
upper 30s-lower 40s) and cell motion is likely to increase. However,
cell coverage is expected to be more isolated compared to Monday.
MJD

HYDROLOGY...
Snowmelt flows with the hot temperatures will continue to be a
concern for the Walker River Basin. At this time, the greatest
impact is expected to be on the West Walker in the Antelope Valley
where moderate flooding is expected. Farther downstream, the
impacts depend on reservoir management and if/when the reservoirs
reach capacity. The Mason Valley including Yerington remains in
the flood advisory with minor lowland flooding expected. The river
will rise higher than anything we have seen so far this spring.
Whether it is only a quarter foot higher, or something more
significant is unknown and will continue to be monitored.

Elsewhere, high flows will continue on the Mono County streams
draining the Sierra with minor flooding likely in some areas.
High flows will also continue on the Carson and Truckee basins,
but no flooding is expected. Wallmann

&&

.REV Watches/Warnings/Advisories...
NV...None.
CA...None.
&&

$$

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



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