Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 272104
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
204 PM PDT WED JUL 27 2016

.SYNOPSIS...

Hot and dry conditions will prevail this week with a few record
highs possible. A slow increase in moisture will lead to a few
afternoon and evening thunderstorms, especially by Friday. High
temperatures will ease downward early next week as a trough moves
through the Pacific Northwest.

&&

.DISCUSSION...

Upper ridge of high pressure will remain anchored across the
region through Friday with temperatures warming to near record
levels. Models have trended equally hot for Friday as 700mb temps
push 18-19C. The only fly in the ointment would be sky cover
Friday as moisture gradually increases. The GFS is more robust
with cloud cover but believe the ECMWF might have a better handle
on the large scale moisture/cloud cover fields, increasing the
clouds later in the day from the convection as opposed to
advecting cloud cover across the area. Latest satellite imagery
showed little cloud cover in the area where moisture is forecast
to originate and this would support a more sunny start. Thus,
strong thermal heating will be capable of pushing temps to MOS
guidance prior to convection and cloud cover initiation each day.
Current forecast highs will result in a few broken records and
push the heat indices into critical levels across the Basin and
Range through Friday.

While large scale forcing will be absent, moisture gradually moves
northward along the eastern Sierra in light south flow underneath
ridge and will combine with intense surface heating and small
scale convergence along terrain/zephyr to produce isolated storms.
This convection will be mostly limited to Mono County and far
western Mineral County late Thursday, but then spreads northward
Friday, possibly reaching the Lassen County convergence by Friday
evening. Due to high bases and limited moisture/narrow cores, the
primary threat will be strong outflow winds to 50+ mph, especially
with storms that move out over the lower and hotter valley floors.
A trough will move into the Pacific Northwest this weekend and
gradually push the moisture and instability out of the area.
However, isolated storms will once again form each afternoon
through Sunday with best chances south of Hwy 50.

By Monday or Tuesday, conditions should become stable enough to
preclude any mention of thunderstorms even across southern areas,
although confidence in a complete drying trend is only medium at
this time. Temperatures should finally drop back towards more
normal levels by early next week, although we slowed the cool down
by a couple of degrees each day given latest MOS guidance from
both the GFS/ECMWF.

Smoke from the Soberanes Fire south of Monterey Bay was making a
more eastward push this afternoon and will probably keep some haze
going through this evening. By Thursday and into the weekend,
finer scale models keep the smoke plume trajectory well south of
our area. Mixing over the next couple of days should disperse the
haze more and thus we will not be extending a mention beyond this
evening. Hohmann

&&

.FIRE WEATHER...
Hot, dry conditions to continue into Friday with very low afternoon
humidity and poor overnight recovery, especially for mid slopes and
ridges. The main concern for the next couple days will be the threat
of thunderstorms. Cumulus is forming over Mono County this afternoon
and we do not expect any thunderstorms to fire, although one is
certainly possible (the chances are less than 10%).

Thursday, a little more moisture seeps in. With better instability
and continued hot temps, isolated thunderstorms are possible near
the Sierra Crest south of Tahoe slowly spreading through Mono County
into the Sweetwaters into the evening. While we don`t have any
thunderstorms north of Tahoe because the chances are quite low, one
area that may pop a storm would be near Sage Hen Summit north of
Truckee.

Moisture will continue to seep northward Friday under light south
flow. Overall instability isn`t that great and it looks like just a
few storms may fire all along the crest up to 50 miles east.
However, we have underdone these thunderstorm patterns on the
backside of previous heat waves. We are quite confident in a few
storms, but there could be quite a bit more. Our confidence is
quite low at this time with regard to coverage Friday. That said,
with the fuels very dry, ignition efficiency could be quite high.
Therefore, we issued a fire weather watch for these areas except
for the Tahoe Basin. We left the basin out as the lake acts as a
stabilizing influence with the marginal instability. Most storms
if they form, would be on the east side, in the Carson Range.

Southwest flow then begins Saturday with the limited moisture
pushing east. A few storms remain possible near the Oregon border
and Mono/Mineral Counties Saturday, and only the southern areas
Sunday. One thing to watch if this does end up being a decent
event will be the increase in winds Monday-Tuesday. They do not
look that strong, but gusts to 30 mph are possible.

&&

.AVIATION...

VFR conditions prevail through Thursday, with a few cumulus buildups
this afternoon over Mono County. By Thursday, isolated afternoon
thunderstorms are possible for Mono and Alpine counties, with a
small 10-15% chance of a storm affecting KMMH. By Friday, the threat
for isolated thunderstorms expands northward and may affect
KRNO/KCXP/KSVE. The storms are less likely to directly affect
terminals near the Tahoe basin.

Gusty downdraft/outflow winds will be the main threat with these
storms. Most of the storms will produce limited precipitation except
near the cores, so visibility at the surface may only be restricted
if the outflow winds kick up some blowing dust.

Some haze from central CA wildfires will linger today, but produce
few significant aviation impacts other than minor slantwise
visibility reductions. After today, the main push of smoke from
these fires is expected to remain well west and south of the Sierra.
MJD

&&

.REV Watches/Warnings/Advisories...
NV...Fire Weather Watch from Friday afternoon through Friday evening
     NVZ450-458-459.

     Heat Advisory until 11 PM PDT Friday NVZ001-004.

CA...Fire Weather Watch from Friday afternoon through Friday evening
     CAZ270-271-273-278.

&&

$$

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


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