Simpson, Nevada Weather Forecast Discussion

633
FXUS65 KREV 211822
AFDREV
Area Forecast Discussion
National Weather Service Reno NV
1122 AM PDT Sun Sep 21 2025
.KEY MESSAGES...
* Showers and isolated thunderstorms this afternoon, mainly for
  northeast CA, northwest NV and Mono, Mineral and southern Lyon
  counties.
* Near to slightly above average temperatures are expected
  through much of the upcoming week.
* Another weather system may bring shower and thunderstorm
  chances again by mid-late week.
&&
.DISCUSSION...
* For this afternoon-early evening, two areas are at risk for
  isolated shower and t-storm activity with precip chances around
  15-25%. The first area is northeast CA-northwest NV where a weak
  trough passage has already produced a few showers in Lassen
  County. These showers will continue to move/develop to the east-
  southeast with most activity remaining north of Pyramid Lake.
  However, some of the latest high-res guidance allows for a few
  stray cells to form farther south to near I-80 in far western NV
  around the 4-6 PM time frame (about 10% chance). The second area
  is Mono-Mineral and southern Lyon counties, where lingering
  instability and a weak deformation zone extending from an upper
  low off the southern CA coast should also allow for isolated
  shower/t-storm activity mainly after 2 PM. Any storms that do
  form will be capable of lightning, brief heavy rainfall, and
  gusty winds, before most activity winds down by 8-9 PM.
* For Monday-Tuesday, a high pressure ridge off the northern CA
  coast will build inland over northern CA-NV and bring dry
  conditions with temperatures near or slightly above average
  (highs in the lower-mid 80s for western NV and mid-upper 70s
  near the Sierra). The latest guidance is trending drier for
  Tuesday with the ridge delaying the northward progress of
  deeper moisture circulating around an upper low off the southern
  CA coast.
* For mid-late week, the latest round of medium range guidance
  favors a slow inland track for this upper low into southern CA.
  Deeper moisture and increasing shower/isolated t-storm chances
  spread northward to the Sierra (30-40%) during the day Wednesday
  and reach their northernmost extent into much of western NV and
  parts of northeast CA (15-30%) by Wednesday evening and
  overnight. Showers and isolated t-storms then continue Thursday
  mainly from I-80 southward with best overall chances (30-40%)
  over Alpine-Mono counties. More of the guidance also favors
  lingering precip chances mainly south of US-50 through Friday as
  this low slowly drifts into southern AZ. While a more northerly
  storm track with precip spreading farther north of I-80 for
  Thursday-Friday can`t be ruled out, that scenario has trended
  less likely with the latest ensemble projections.
* Next weekend is looking mainly dry with high pressure hanging on
  over northern NV, although if the low is slow to leave the
  southwest US, some lingering moisture and east flow could keep
  low-end shower chances going for the eastern Sierra and Mineral
  County. Temperature wise, warmer than average conditions are
  likely to continue, with next potential for some cooling toward
  the end of September. MJD
&&
.AVIATION...
* For KMMH through this evening: Shower/storm chances near 25%
  today between 21-02Z, which may bring brief heavy rain with MVFR
  ceilings and wind gusts to 30 kts.
* Elsewhere at the main terminals through Tuesday: VFR conditions
  with mainly light winds (gusts below 20 kt) prevail. Only
  exception is patchy fog around KTRK between 10-16Z Monday
  morning with periods of MVFR to LIFR conditions. MJD
&&
.REV Watches/Warnings/Advisories...
NV...None.
CA...None.
&&
$$

NWS REV Office Area Forecast Discussion