653
FXUS65 KREV 212120
AFDREV
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RENO NV
220 PM PDT MON SEP 21 2026
KEY MESSAGES
* SHOWER AND THUNDERSTORM CHANCES ARE IN THE FORECAST THIS AFTERNOON
AND EVENING, ESPECIALLY FOR THE SIERRA AND SOUTH OF US-50.
* WARMER AND GENERALLY DRY CONDITIONS ARE EXPECTED MID-WEEK WITH
TEMPERATURES 5 TO 10 DEGREES ABOVE AVERAGE.
* INCREASED WINDS AND COOLER TEMPERATURES RETURN TOWARDS THE END OF
THE WORK WEEK.
DISCUSSION
THE LATEST FORECAST GUIDANCE PROJECTS LOW PRESSURE CURRENTLY OVER
CENTRAL CA TRAVELING EAST-NORTHEASTWARD INTO THE GREAT BASIN LATER
TODAY. CURRENT RADAR IMAGERY SHOWS THAT A FEW SHOWERS AND
THUNDERSTORMS HAVE ALREADY DEVELOPED WITHIN THE CWA. GOING
THROUGH THE REST OF TODAY, THE FORECAST CALLS FOR AROUND A 15-50%
CHANCE FOR SHOWERS GENERALLY FOR THE SIERRA AND PORTIONS OF THE
REGION SOUTH OF US-50 WITH THE HIGHER END CHANCES IN MONO AND
MINERAL COUNTIES. COVERAGE ALSO EXTENDS A BIT NORTH INTO WESTERN
LASSEN COUNTY WHERE THERE IS A ~15% CHANCE FOR PRECIPITATION. WHEN
LOOKING AT CAM CONVECTIVE PARAMETERS, CAPE VALUES WILL BE AROUND
250-500 J/KG TODAY, WHICH WILL ALLOW FOR A 10-15% CHANCE FOR
THUNDERSTORMS TO DEVELOP WITHIN THE SHOWERS. STORMS THAT FORM
TODAY WILL BE CAPABLE OF OCCASIONAL LIGHTNING STRIKES, OUTFLOW
WIND GUSTS UP TO 45 MPH (WHICH COULD BLOW DUST NEAR DESERT SINKS),
AND BRIEF PERIODS OF HEAVY RAINFALL. SOME MODELS ARE ALSO SHOWING
POTENTIAL SNOW WITH THESE SHOWERS IN PORTIONS OF THE SIERRA ABOVE
10.5 KFT THOUGH AMOUNTS RANGE FROM A TRACE TO UNDER 1 INCH.
PLEASE BE WEATHER AWARE TODAY ESPECIALLY IF YOU HAVE OUTDOOR
PLANS. ELSEWHERE, DRY CONDITIONS LOOK TO PERSIST THROUGH THE DAY.
MODEL GUIDANCE SHOWS THE LOW PROGRESSING OFF TO THE NORTHEAST ON
TUESDAY AS A WEAK RIDGE FEATURE MOVES OVER THE REGION IN ITS WAKE
GOING INTO WEDNESDAY. THE TRAJECTORY OF THE LOW MAY ALLOW FOR
SOME LINGERING ISOLATED SHOWER CHANCES (~15%) IN FAR NE CA AND
ADJACENT WASHOE COUNTY AS WELL IN THE NV BASIN AND RANGE DURING
TUESDAY AFTERNOON. DRY CONDITIONS WILL FOLLOW LATE TUESDAY THROUGH
WEDNESDAY. DAYTIME HIGH TEMPERATURES WILL CLIMB TO AROUND 5-10
DEGREES ABOVE SEASONAL NORMALS BY WEDNESDAY WITH NE CA AND W NV
VALLEYS TOPPING OUT IN THE MIDDLE TO UPPER 80S WITH SIERRA
COMMUNITIES IN THE 70S.
WHILE THURSDAY HAS SIMILAR TEMPERATURES TO THOSE ON WEDNESDAY IN THE
FORECAST, MODEL GUIDANCE SHOWS AN UPPER TROUGH MOVING INTO PAC NW
BEGINNING LATE THURSDAY. THIS FEATURE WILL CAUSE A TIGHTER PRESSURE
GRADIENT AT THE SURFACE, WHICH ALLOWS FOR STRONGER WINDS ON THURSDAY
AND FRIDAY COMPARED TO THE LIGHTER WINDS EXPERIENCED EARLIER IN
THE WEEK. THE LATEST FORECAST CALLS FOR GUSTS UP TO AROUND 25-35
MPH WITH A 30-60% CHANCE OF EXCEEDING 35 MPH IN THE SIERRA FRONT
ON BOTH DAYS. PRECIPITATION CHANCES REMAIN UNCERTAIN, BUT THE
FORECAST IS CURRENTLY SHOWING THE DRY PATTERN PERSISTING THROUGH
THE LATTER HALF OF THE WEEK. TEMPERATURES BEGIN TO TREND COOLER ON
FRIDAY AS A POTENTIAL DRY COOL FRONT ASSOCIATED WITH THE
AFOREMENTIONED TROUGH MOVES THROUGH THE REGION, CAUSING DAYTIME
HIGHS TO BECOME AROUND 5 DEGREES BELOW SEASONAL AVERAGES BY THE
BEGINNING OF NEXT WEEK. -078
AVIATION
MOST AREA TAF SITES EXPECT TO SEE VFR CONDITIONS FOR THE REST OF
TODAY AND TONIGHT. KMMH COULD SEE SUB-VFR CONDITIONS AS THERE IS A
20-50% CHANCE FOR SHOWERS AND THUNDERSTORMS IN THE SIERRA AND
SOUTH OF US-50 GOING THROUGH AROUND 22/05Z WITH HIGHER END
CHANCES IN MONO AND MINERAL COUNTIES. STORMS THAT OCCUR IN THE
REGION COULD PRODUCE ERRATIC OUTFLOW WIND GUSTS UP TO AROUND 40
KTS AND BRIEF PERIODS OF HEAVY RAINFALL. LESSER PRECIPITATION
CHANCES (~15%) ARE SEEN TOMORROW AFTERNOON FOR AREAS ALONG THE OR
BORDER AND IN THE NV BASIN AND RANGE. -078
REV WATCHES/WARNINGS/ADVISORIES
NV...NONE.
CA...NONE.
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