Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 162132
AFDREV

Area Forecast Discussion
National Weather Service Reno NV
232 PM PDT Sun Jul 16 2017

.Synopsis...

Buildups with isolated thunderstorms are expected this afternoon
and evening over the eastern Sierra into central Nevada. Low
pressure approaching the west coast will increase winds Monday and
Tuesday, leading to critical conditions for rapid fire spread.
Decreased winds with hot temperatures are forecast for the balance
of next week, with isolated storms confined to mountain areas.

&&

.Discussion...

* Thunderstorm Trends: Isolated storms remain in the forecast
  through this evening following latest HRRR guidance. Satellite
  showing decent buildups over higher terrain from Alpine Co south
  and eastward into central Nevada. This is the area we`re
  watching for possible storms. No severe nor flash flood storms
  expected but new fire starts from lightning and strong outflow
  winds are possible. Airmass dries out and stabilizes starting
  Monday as southwest flow aloft increases. This should push storm
  chances out of our region through at least Wednesday.

* Radar Status: The Reno KRGX radar is inoperative until further
  notice. An apparent motor failure is being investigated by
  technicians this afternoon. We`ll hopefully have a better handle
  on when the radar will return to service then. Use of
  surrounding radars such as Sacramento or Elko may help but
  details won`t be as clear over our region. GOES-16 data and
  lightning networks will prove useful for storm monitoring this
  afternoon.

* Increased Winds Monday, Tuesday: Low pressure off the Pac NW
  will yield increased southwest flow aloft and stronger than
  normal mid-summer winds early this week. While not terribly
  impactful for travel, this could be a big scenario for fire. See
  fire weather section for more details. Choppy waters will be
  encountered on most area lakes, so Lake Wind Advisories will be
  posted for Monday.

* Storm Trends Late Week: High pressure will build back over the
  region bringing generally quiet and hot weather through next
  weekend. But not excessively hot. Isolated storms could return
  to the Eastern Sierra starting Thursday afternoon. GEFS/ECMWF
  simulations continue to suggest a big monsoon moisture push into
  our region early-mid next week. This would result in more
  widespread thunderstorms and a possible flash flood scenario,
  something we haven`t seen much of so far this summer. Confidence
  remains mixed but worth monitoring.

-Chris

&&

.Aviation...

* Areas of haze and smoke from Long Valley fire earlier resulted
  in MVFR visibilities around RNO and RTS. With now increasing
  winds and mixing visibilities will steadily improve. Typical
  afternoon and evening westerly winds today will transition to
  northwest overnight. This could lead to smoke and haze back into
  RNO/CXP vicinity by daybreak Monday. Surface visibility
  restrictions should be MVFR at worst with slantwise visibility
  being poorer.

* Isolated storms remain possible this afternoon-evening, mainly
  for areas south of TVL-CXP-NFL line into the Eastern Sierra
  (MMH). Based on latest HRRR guidance and satellite trends this
  looks reasonable. Note that Reno RGX radar is out of service
  until further notice so radar data over the region will be
  degraded.

* Low pressure approaching Pac NW early this week. Increased
  west/southwest winds Monday and Tuesday likely to yield some
  turbulence and localized wind shear. Could impact fire air
  support ops. Gusts on the order of 30-35 kts likely including
  RNO/CXP and Long Valley Fire area each afternoon and evening.
  Not a huge wind event but there will be some bumps.

-Chris

&&

.Fire Weather...

The forecast remains on track for an extended period of fire
weather concerns through about mid-week. Gusty winds and very low
RH will combine to create critical fire weather conditions Monday
and Tuesday with a more marginal, but non-zero, risk Wednesday.

Monday`s conditions continue to pose the largest concerns with a
projected 9-12 hour period of critical fire weather conditions. A
trough dropping out of the Pacific Northwest will strengthen the
wind field with gusts expected in the 30-40 mph range. Winds
linger into the overnight hours especially along upper slopes and
ridges. A significant dry slot will also accompanying this trough
resulting in lower than usual afternoon humidity, 4-10% in western
Nevada, and abysmal overnight recoveries. Downwind of existing
wildfires, like the Long Valley and MM155 fires, Sutcliffe and
Grass Valley south of Winnemucca are in a higher threat area. This
is a particularly dangerous situation where fire spread rates may
greatly exceed fire protection ability. You may have very little
time to leave, so it is best to heed any evacuation orders.

Winds increase again Tuesday afternoon to a slightly lesser
degree, gusts 25-35 mph, as the pressure gradient remains
relatively tight. Hours under red flag conditions decreases from
Monday to 3-7 hours Tuesday. As such, the Fire Weather Watch has
been upgraded to a Red Flag Warning. Any active fires will
intensify once again reducing the effectiveness of fire
suppression measures.

Winds Wednesday have been subtly increasing each new model run.
Concerns are increasing, but no watches or warnings have been
issued yet. Some of the higher slopes and ridges will briefly meet
critical thresholds, but the duration is currently projected to
be only around a couple of hours. Overall, conditions are expected
to be more marginal. However, as we have seen this season, fires
involving grasses and sage will be very active even in marginal
conditions.

Finally, smoke and haze around the Reno Metro area has been
reducing Air Quality during the overnight and morning hours
beneath nocturnal inversions. Recent readings in Reno have shown
that air quality has degraded into the "Unhealthy for Sensitive
Groups" rating. Locations closer to active fires, like Palomino
Valley and Pyramid Lake, will have worse conditions. As long as
fires are burning in close proximity to Reno and other populated
areas, expect poor to moderate air quality. Boyd

&&

.REV Watches/Warnings/Advisories...
NV...Red Flag Warning from noon to 8 PM PDT Monday NVZ450-453-458-459.

     Red Flag Warning from noon to 8 PM PDT Tuesday
     NVZ450-453-458-459.

     Lake Wind Advisory from noon to 8 PM PDT Monday NVZ002>004.

CA...Red Flag Warning from noon to 8 PM PDT Monday CAZ270-271-278.

     Red Flag Warning from noon to 8 PM PDT Tuesday CAZ270-271-278.

     Lake Wind Advisory from noon to 8 PM PDT Monday CAZ071>073.

&&

$$

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



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