Area Forecast Discussion
Issued by NWS Reno, NV

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504
FXUS65 KREV 182110
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
210 PM PDT Tue Jul 18 2017

.SYNOPSIS...

Increased thermal and pressure gradients associated with a trough
of low pressure along the West Coast will keep winds elevated
this evening, leading to increased fire danger. As this trough
weakens and the gradients decrease over the next few days, late
afternoon winds will become more typical of mid-summer. Dry
conditions with near seasonal temperatures will continue through
the week.

&&

.DISCUSSION...

Minimal changes were made to the forecast this cycle as model
guidance supports the current trends of keeping the forecast dry
under southwest flow aloft with a gradual lessening of the winds
over the next couple of days. After of few days of relative "cool"
near normal high temperatures...highs will warm by the end of the
week and the weekend to above normal once again.

Continued strong southwest flow aloft with very dry air in place
will lead to gusty winds this afternoon and low humidity. There
remain Red Flag Warnings and Lake Wind Advisories in place. See
the Fire Weather section below for more details on critical fire
weather conditions. As the winds aloft decrease Wednesday and
Thursday...we will see a gradual decrease in afternoon winds to a
more typical zephyr with gusts approaching 25-30 mph instead of
more than 30 mph.

Even though the flow aloft decreases it remains southwesterly.
That should keep moisture from making its way north through
Friday. By Saturday high pressure starts to rebuild into the
region from the southeast. That will allow for increasing heights
and warming aloft that will translate to high temperatures working
their way back into the mid to upper 90s for western Nevada and
northeast California and the mid to upper 80s in the Sierra
valleys.

Southerly flow aloft tries to become a bit more established by
Sunday. The GFS and ECMWF are both trying to lift a short wave
northeast through the flow Sunday...but the GFS is more
aggressive. Its solution would bring the possibility of showers
into the forecast by late Sunday night into Monday morning. As
this is not well supported by the ECMWF we have opted to leave the
mention of showers out of the forecast for now. The short wave
lifts out Monday leaving weak flow aloft in its place.

For Tuesday...the models are at odds with the development of the
overall pattern. The GFS reverts to southwest flow while the ECMWF
tries to shift to a more west-northwest flow pattern. Both of
these are dry...but have some implications to the wind and
temperature forecasts.

As stated in previous discussions...the models continue to try to
bring a pseudo-monsoon surge into the region next week...but keep
pushing its arrival further out in time. Today the GFS brings
this surge back next Thursday while the ECMWF does not show this
push within the next 10 days. Thus...confidence remains low in any
return to an active thunderstorm pattern through the middle of
next week.

&&

.AVIATION...

The combination of haze and smoke from active fires in northern
Nevada and California may limit flight level and slant-wise
visibility through the next 24 hours. The most likely areas with
the greatest reduction in visibility will be in the vicinity
of...or downwind of...actively burning fires. Outside of these
areas of haze and smoke we will see continued VFR conditions.

Gusty winds above the ridges should continue to create periods of
turbulence aloft through late tonight. Gusty surface winds this
afternoon will decrease during the evening. Winds aloft and near
the surface decrease Wednesday through the remainder of the week.

Beyond Wednesday...delineating areas of smoke that may reduce
visibility becomes difficult as the forecast depends upon how
active any current fires become and whether new fires develop.

&&

.FIRE WEATHER...

Red Flag Warnings remain in effect through this evening for a
combination of gusty winds and low humidity. RAWS sensors across the
region are starting to report critical conditions with wind gusts
largely in the the 25-35 mph range. The peak wind gusts are
currently ongoing and are expected to begin to diminish after about
8pm this evening.

Winds will remain breezy across ridges and midslopes so poor
humidity recoveries are expected overnight (20-35%). Winds will
lighten through the week but will still remain breezy Wednesday
where wind gusts of 25-30 mph will still be possible during the
afternoon and early evening. Although these winds are just below Red
Flag Warning criteria, the combination of breezy conditions and a
very dry air mass in place will continue elevated fire concerns
through at least Thursday as recent fires have shown a tendency to
spread with these wind speeds so caution is still advised.

The very dry airmass is expected to remain in place much of this
week. As such, this will keep chances for showers and thunderstorms
out of the forecast until we can get some moisture transport into
the region. Currently, models show some hints of this occurring by
the end of the weekend and into early next week as they develop a
weak low offshore of the northern California coast. We will continue
to monitor this trend. Fuentes

&&

.CLIMATE...

The airport in Reno has already reached a temperature of 93
degrees today...running the current streak of days with a high of
90 degrees or higher to 33...2 days shy of tying the record.
Given the normal highs at Reno this time of year are 90 degrees or
higher through August 21 and the current trend of dry and warm
conditions continuing into the weekend...we should be able to
eclipse this old record. The high yesterday failed to reach 95
degrees...ending that streak at 17 days...just 2 days short of
tying the record.

&&

.REV Watches/Warnings/Advisories...
NV...Red Flag Warning until 8 PM PDT this evening NVZ450-453-458-459.

     Lake Wind Advisory until 8 PM PDT this evening NVZ003-004.

CA...Red Flag Warning until 8 PM PDT this evening CAZ270-271-278.

     Lake Wind Advisory until 8 PM PDT this evening CAZ071.

&&

$$

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



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