Fire Weather Watch 6, NWS Reno, NV

Area Forecast Discussion
National Weather Service Reno NV
413 AM PDT Sat Jun 26 2021

.SYNOPSIS...

Heat begins to build today into the middle part of the coming week.
Thunderstorm chances increase near the Sierra crest Sunday through
Monday before expanding to most areas the latter half of next
week.

&&

.DISCUSSION...

The biggest change to the forecast was to increase thunderstorm
chances near the Sierra crest Sunday and Monday, before expanding
chances across the region into the later part of next week. We also
upgraded the Excessive Heat Watch to a Heat Advisory for Lassen-
Eastern Plumas-Eastern Sierra Counties through 10 PM PDT Wednesday.
The big story turns to the building heat into next week with the
return of thunderstorms, especially Tuesday onward.

Today through Sunday morning:

* A upper ridge off the coast of Baja California will strengthen
  northward into California and western Nevada today. Temperatures
  will begin to increase to 5-10 degrees above normal this afternoon
  before the influence of a very anomalous ridge over the Pacific
  Northwest increases heights and subsidence across much of the
  region into the middle part of the week. Thunderstorms are not
  expected today due to the strong mid-level CAP formed due to
  strong subsidence and warming aloft.

Sunday through Friday:

* The upper-level ridge will strengthen overhead, generating strong
  subsidence and significant heating at the surface. Most valley
  areas below 5000 feet will feel the heat early this coming week as
  afternoon temperatures increase into the upper 90s and 100s. The
  hottest areas will be many of the lower valleys of the Basin and
  Range where afternoon highs could reach 104-106 degrees. Record
  afternoon heat is a possibility especially Sunday through Tuesday
  across western Nevada per the latest NBM and ECMWF EFI guidance.
  Dry conditions will allow for good radiational cooling, which will
  keep lows in the 60s across the lower valleys of western Nevada.

* Thunderstorm chances begin to creep back into the forecast
  beginning Sunday afternoon west of the central Sierra crest due
  to easterly synoptic flow. Monday afternoon, storms will
  initially favor the west side of the Sierra crest, but outflows
  may allow storms to push near and east of the crest later in the
  afternoon. Higher PWATs then begin to spread northward across
  the region Tuesday through Friday as the North American monsoon
  ramps up. This increased moisture will build instability across
  the region, allowing for thunderstorm chances to increase area-
  wide as the upper-level ridge moves eastward over the northern
  Intermountain West/Rockies and an upper-level low sets up just
  west of the Baja peninsula. This may produce an ideal setup for
  slow-moving storms with heavy rainfall, which could bring flash
  flood concerns. However, uncertainty remains high in the exact
  movement of the upper-level features across the western half of
  the country. We'll get a better idea as we get closer to the
  middle part of the week.

-Johnston

&&

.AVIATION...

Storm chances are less than 10% over the Sierra this weekend and
less than 5% across western NV and northeast CA as a strong ridge of
high pressure begins to build over the west. With near record heat
possible, density altitude concerns will return. Winds will be
mostly light with a general light northeast to east flow.

For next week, Monday and beyond, winds will turn more southeasterly
and allow for moisture to gradually increase along the Sierra Monday-
Tuesday and then expand to most areas for the last half of the week.
The threat of thunderstorms will be on the increase next week.

Hohmann

&&

.REV Watches/Warnings/Advisories...
NV...Excessive Heat Warning from 2 PM Sunday to 10 PM PDT Wednesday
     NVZ004.

     Heat Advisory from 2 PM Sunday to 10 PM PDT Wednesday
     NVZ001-003-005.

CA...Heat Advisory from 2 PM Sunday to 10 PM PDT Wednesday CAZ070-071.

&&

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