Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 181024
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
324 AM PDT Mon Sep 18 2017

.SYNOPSIS...

A series of cold fronts will produce gusty winds today and again
Wednesday. Below average temperatures are expected for much of the
upcoming week, with the coolest days most likely Thursday and
Friday. Light showers, with a dusting of snow in higher
elevations, are possible at times from Wednesday through Friday,

&&

.SHORT TERM...

The transition to a more active weather pattern with much cooler
temperatures and chances for showers (including a bit of snow
possible for the mountains) is still on track for this week, as
longwave trough digs into the western US.

* Winds:

Today and Wednesday will feature windy conditions, in
association with a pair of cold front passages, while winds on
Tuesday should be lighter in between these weather systems. In
general, gusts of 35-45 mph with Sierra ridge gusts up to 75 mph
are expected for this afternoon and evening.

For Wednesday, wind gusts may be slightly greater, as the timing
of the stronger mid level flow ahead of the cold front passage
appears to occur at a more favorable time of day (late afternoon
instead of early- mid evening), and the upper level jet on
Wednesday is stronger and digs farther south compared to today.

* Precipitation:

Today`s cold front lacks significant moisture, although some
forcing along the front could produce some very light showers in
parts of northwest NV and far northeast CA this evening. Also,
short range guidance is indicating a bit of terrain-induced lift
with low level moisture across the Sierra crest near the Tahoe
basin, which could trigger a few showers in this area during the
evening. For both of these areas, precip totals will be quite
sparse with only a few locations receiving measurable amounts.

After generally dry conditions Tuesday, a better moisture tap sets
up Wednesday-Wed night, with stronger jet dynamics also coming
into play to increase precip chances. During the day, most of the
shower activity will likely be limited to northeast CA-northwest
NV, then swing south into the Sierra and western NV during the
night.

Precip amounts are not expected to be very significant, but
some locations in the Sierra, far northwest NV/Surprise Valley,
and the Basin and Range east of US-95 could receive around 0.10
inch. Snow levels may drop to near 7000 feet by late Wed night,
although if any light snow accumulations occur, they are more
likely to be confined to higher peaks.

* Temperatures:

The first round of cooling will be most noticed north of
Susanville-Gerlach later today, where highs may come up short of
70 degrees. Otherwise, today`s highs will generally range from the
mid 70s-lower 80s for lower elevations. On Tuesday, all areas
will see several degrees of cooling behind the first cold front.

On Wednesday, areas north of Susanville-Gerlach will again be
coolest as widespread cloud cover and shower chances may keep
highs near or below 60 degrees. Otherwise, highs should be similar
to Tuesday, with parts of the US-95 corridor possibly a bit
warmer due to strong mixing prior to the cold front`s arrival.
The next few evenings/nights (especially Wednesday) will feel
more chilly compared to recent nights due to the combination of
the cooler air mass and gusty winds. Time to bring out the jackets
if planning to be outdoors after sunset this week. MJD

.LONG TERM...Thursday through Sunday...

In the wake of a cold front and upper level wave that moves through
the region Wednesday/Wednesday night...the forecast area should
settle under an upper level trough that hangs around through at
least early Saturday before the trough starts to push east.

The presence of the upper level trough...and attendant short waves
rotating around it...should result in isolated to widely scattered
showers Thursday and Friday. At this point trying to pinpoint exact
locations will be difficult and confidence remains fairly low
regarding the actual pops. For now we will leave the area under
mostly slight chance to low end chance pops with the best coverage
likely over the far northern parts of the forecast area and along
the Sierra from about Highway 50 south through Mono County. By
Saturday...as the trough starts moving east and ridging develops...
no precip is expected.

Turning our attention to temperatures...the highs were lowered a
little bit again for Thursday through Saturday. Highs in the 60s
should be common across the lower valleys with 50s in the Sierra
valleys. That is about 15 degrees below normal in many areas.
Likewise...the lows should be well below normal with many lower
valleys dipping into the upper 30s to lower 40s for Thursday and
Friday morning. The Sierra valleys could drop below freezing in some
of the colder areas with lows in the mid 20s in areas like
Bridgeport. These typically colder valleys could see their first
substantial freeze and anyone with sensitive vegetation in these
colder valleys should make preparations to protect said vegetation.
Lows will climb a bit by Saturday.

&&

.AVIATION...

Cloud cover should increase over areas north of I-80 today as a cold
front moves into the region. Gusty winds ahead of this front will
develop through the morning hours. Surface gusts could reach 30-35
kt from I-80 northward with gusts in the 25-30 kt range to the
south. Ridge gusts could top 60 kt later today and this evening.
Turbulence and low level wind shear is highly likely today and
tonight. Shower chances are rather slim with this front...but a few
areas north of a line from Susanville to Gerlach could see
slightly lower ceilings.

Showers linger near the Oregon border Tuesday but winds will be
lighter overall. The next significant system impacts the region
starting Tuesday night and Wednesday. Initially there will be an
increase in clouds and a lowering of ceilings near the Oregon
border Tuesday night with a few more showers. This will expand
south during the day Wednesday into the overnight hours. Showers
with some reduction in ceiling will be possible north of I-80 and
down into the northern Sierra by Wednesday afternoon; these move
farther south Wednesday night. But the more impactful feature will
be increased winds. Surface gusts could reach 40 kt or more
Wednesday with ridge gusts closer 70 kt. This is likely to result
in more widespread turbulence than today.

&&

.FIRE WEATHER...

Strong winds aloft combined with an approaching cold front and its
increased pressure and thermal gradients should lead to surface wind
gusts in the neighborhood of 35-45 mph across the eastern parts of
Lassen County into western Nevada today. This strong wind combined
with humidity values dipping into the 12-24% range will likely
create critical fire weather conditions in some areas today.
Normally we look for lower humidity...but the very strong wind gusts
should be able to carry fire through grasses and small brush. The
areas with Red Flag Warnings are zones 278...450...453 and the
southern half of 458.

North of this area...near the Oregon Border...humidity levels will
rise too fast for conditions to become critical over a broad area.
To the west in zones 271 and 272...humidity will also be a little
higher. To the south the lower elevations of zone 273 and much of
459 will see lower humidity values...but the winds should not be
quite as strong over a broad area. Still...locally critical
conditions are possible in these zones...especially near Walker Lake
and in the lower valleys along Highway 395 in Mono County.

Another round of very strong winds is likely for Wednesday as
another cold front moves through the region. Humidity levels are
likely to rise faster behind this front...but there could still be a
period of critical conditions from late Wednesday morning into the
afternoon. For now we will hold off issuing any watches or warnings
for this event...but they are possible.

&&

.REV Watches/Warnings/Advisories...
NV...Red Flag Warning from 11 AM this morning to 10 PM PDT this
     evening NVZ450-453-458.

     Lake Wind Advisory from 10 AM this morning to 10 PM PDT this
     evening for Lake Tahoe in NVZ002.

     Lake Wind Advisory from noon today to 10 PM PDT this evening for
     Pyramid Lake in NVZ004.

CA...Red Flag Warning from 11 AM this morning to 10 PM PDT this
     evening CAZ278.

     Lake Wind Advisory from 10 AM this morning to 10 PM PDT this
     evening for Lake Tahoe in CAZ072.

&&

$$

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



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