086
FXUS65 KREV 201017
AFDREV
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RENO NV
317 AM PDT MON JUL 20 2026
KEY MESSAGES
* AFTERNOON SHOWER AND THUNDERSTORM CHANCES EACH DAY THIS WEEK,
BECOMING WIDER IN AREAL COVERAGE THROUGH MIDWEEK.
* ABUNDANT MOISTURE AND SLOWER STORM MOTIONS WILL INTRODUCE FLASH
FLOODING POTENTIAL FROM HEAVY RAINFALL AS THE MAIN CONCERN
TODAY AND TOMORROW.
* UNCERTAINTY LATER THIS WEEK INTO NEXT WEEKEND ON WHETHER THE
MONSOONAL PATTERN WILL PERSIST OR IF DRIER CONDITIONS EMERGE.
DISCUSSION
CURRENTLY, THE CWA IS UNDERNEATH AN UPPER RIDGE ENCOMPASSING
GENERALLY THE WESTERN TWO-THIRDS OF THE CONUS WITH HIGH PRESSURE
OVER THE FOUR CORNERS REGION. MODEL GUIDANCE HAS THIS PATTERN
PERSISTING TODAY THOUGH THE HIGH PRESSURE PROGRESSES ESE A BIT
INTO THE GREAT PLAINS OVERNIGHT. WITH THIS SETUP ALOFT, THE CWA
WILL BE SEEING A GOOD AMOUNT OF MONSOONAL MOISTURE CONTINUE TO
FLOW IN TODAY WITH MODEL PW VALUES RANGING BETWEEN ~0.8-1.2
INCHES. THIS WILL ALLOW STORMS TODAY TO PRODUCE HEAVY RAINFALL AND
WITH MODELS SHOWING SLOWER STORM MOTIONS OUT OF THE S/SE, FLASH
FLOODING IS POSSIBLE TODAY (ESPECIALLY IN SOUTHERN PORTIONS OF THE
CWA WHERE A FLOOD WATCH IS IN EFFECT). AS FOR HOW SHOWERS AND
THUNDERSTORMS DEVELOP TODAY, CAMS ARE SHOWING THEM STARTING TO
INITIATE IN MONO AND MINERAL COUNTIES AROUND 1 PM PT. THE 40-60%
POP CHANCES THEN SPREADS NORTH INTO THE NV BASIN AND RANGE AS
WELL AS THE QUAD COUNTY AREA IN THE LATE AFTERNOON AND CONTINUES
THROUGH THE EVENING. OTHER PORTIONS OF THE CWA SEE AROUND A 15-25%
POPS CHANCE THIS EVENING AS WELL. WHILE PRECIPITATION CHANCES
DIMINISH OVERNIGHT, PORTIONS OF W NV GENERALLY SEE A 10-20% CHANCE
OF LINGERING SHOWERS GOING INTO THE EARLY MORNING HOURS OF
TUESDAY. WITH CAMS SHOWING CAPE VALUES UNDER 1000 J/KG, THERE
LOOKS TO BE A ~20-40% CHANCE FOR THUNDERSTORMS IN THE NV BASIN AND
RANGE AS WELL AS MONO COUNTY THIS AFTERNOON AND EVENING WITH
AROUND 10-15% ELSEWHERE. THUNDERSTORMS THAT DEVELOP COULD BECOME
BORDERLINE SEVERE TODAY AND PRODUCE STRONG, ERRATIC OUTFLOW WIND GUSTS
OF 50+ MPH. KEEP THIS FORECAST IN MIND WHEN MAKING PLANS TODAY AND
HAVE A WAY TO RECEIVE THE LATEST WEATHER ALERTS AND INFORMATION.
WITH THE FLASH FLOODING THREAT, CONDITIONS CAN BECOME EXTREMELY
DANGEROUS QUICKLY. IF YOU ENCOUNTER A FLOODED ROADWAY, REMEMBER:
"TURN AROUND, DON'T DROWN!"
FOR TUESDAY, ANOTHER ROUND OF SHOWERS AND THUNDERSTORMS (~20-80%
CHANCES WITH THE HIGHER END CHANCES IN MONO AND MINERAL COUNTIES)
ARE TO BE EXPECTED ALONG WITH FLASH FLOOD POTENTIAL. WITH CAMS
SHOWING THE PRECIPITATION COVERAGE A BIT MORE WIDESPREAD, THE AREA
THAT MAY SEE HEAVY RAINFALL WILL INCLUDE THE GREATER RENO AREA AND
THE QUAD COUNTIES AS WELL AS PORTIONS OF THE TAHOE BASIN IN ADDITION
TO MONO COUNTY AND THE NV BASIN AND RANGE. MODEL PW VALUES ARE SLIGHTLY
HIGHER ON TUESDAY THAN MONDAY (0.9-1.3 INCHES) DUE TO MONSOONAL
MOISTURE STILL FLOWING IN. WITH SLOW STORM MOTIONS GENERALLY OUT
OF THE SOUTH, TUESDAY LOOKS ANOTHER DAY OF POTENTIAL FLOODING
CONCERN. PLEASE WATCH FOR FORECAST UPDATES ESPECIALLY IN AREAS
THAT SEE HEAVY RAINFALL TODAY IN CASE ANOTHER FLOOD PRODUCT IS
NEEDED. SIMILAR CAPE VALUES TO THOSE ON MONDAY ARE SEEN ON TUESDAY
THOUGH THE LATEST RRFS SHOWS POCKETS OF ALMOST 1500 J/KG OF CAPE
SOUTH OF US-50, MAKING IT SECOND DAY TO WATCH FOR STRONGER
THUNDERSTORMS. FORECAST GUIDANCE SHOWS A SIMILAR EVOLUTION IN
PRECIPITATION TO THAT ON MONDAY WITH CHANCES STARTING IN MONO
COUNTY AND ADJACENT PORTIONS OF NV IN THE AFTERNOON BEFORE BEFORE
COVERAGE SPREADS NORTHWARD THROUGH THE REST OF THE DAY.
EVEN WITH THIS PRECIPITATION POTENTIAL THIS WEEK, W NV VALLEY HIGH
TEMPERATURES ARE FORECAST TO BE IN THE 90S WITH SOME PORTIONS (LOVELOCK
AND FALLON) POTENTIALLY REACHING THE TRIPLE DIGITS. SIERRA COMMUNITIES
GENERALLY WILL SEE HIGHS IN THE UPPER 70S TO 80S RANGE. ON WEDNESDAY,
MODELS FORECAST THE HIGH PRESSURE TO MAKE IT OVER TX/OK WHICH
WILL TAKE SOME (BUT NOT ALL OF THE MONSOONAL MOISTURE) MORE
EASTWARD. AS SUCH, CHANCES FOR SHOWERS AND THUNDERSTORMS DECREASE
TO AROUND 20-40% AND ARE MOSTLY CONFINED TO MONO COUNTY AND THE NV
BASIN & RANGE AT THIS TIME. FOR THE REST OF THE WEEK AND GOING
INTO THE WEEKEND, PRECIPITATION CHANCES ARE CURRENTLY FORECAST TO
LOWER TO WHERE IT MAY DRY OUT BY THE WEEKEND. HOWEVER, SOME MODELS
SHOW SOLUTIONS WHERE THE HIGH PRESSURE RETROGRADES BACK INTO THE
FOUR CORNERS AREA, WHICH MAY CAUSE PRECIPITATION CHANCES TO RISE
INSTEAD. WITH THIS UNCERTAINTY, WE'LL CONTINUE TO MONITOR THIS
GOING FORWARD TO SEE IF MORE MODELS START TRENDING DRIER OR WETTER
FOR THE LATE WEEK. -078
AVIATION
VFR CONDITIONS ARE EXPECTED FOR AREA TAF SITES TO START TODAY, BUT
SUB-VFR CONDITIONS MAY BE PROBABLE AFTER 20/18Z ON ACCOUNT OF
SHOWER AND THUNDERSTORM CHANCES DEVELOPING WITHIN THE REGION
(ESPECIALLY NEAR KMMH WHICH SEES 50-60% POPS). STORMS THAT DEVELOP
WILL LIKELY CAUSE LOWER CIGS/VIS WITH HEAVY RAINFALL DUE TO
MONSOONAL MOISTURE FLOWING INTO THE REGION. STRONG AND ERRATIC
GUSTS UP TO AROUND 40-50 KTS MAY ALSO BE POSSIBLE WITH THUNDERSTORMS
TODAY. WILL CONTINUE TO MONITOR FORECAST MODELS GOING FORWARD AND
AMEND TAFS AS NEEDED WITH THESE SHOWERS AND THUNDERSTORMS.
MOUNTAIN OBSCURATIONS AT AREA TERMINALS ARE LIKELY TODAY DUE TO
THIS PRECIPITATION AS WELL. LINGERING ISOLATED SHOWER CHANCES
(~10-20%) ARE SEEN IN W NV GOING THROUGH THE NIGHT.
ANOTHER ROUND OF SHOWERS AND THUNDERSTORMS IS EXPECTED ON TUESDAY
WITH SIMILAR IMPACTS THOUGH COVERAGE MAY BE A BIT MORE WIDESPREAD
THAN THAT ON MONDAY. -078
HYDROLOGY
WHILE FLOODING FROM HEAVY RAINFALL IS POSSIBLE TODAY AND TUESDAY,
THERE IS LOW CONFIDENCE IN EXACT LOCATIONS AT THIS TIME.
CURRENTLY, THE WPC GIVES MONO, S. DOUGLAS, S. LYON, AND MINERAL
COUNTY PORTIONS OF THE REGION A MARGINAL RISK (AT LEAST 5%) FOR
EXCESSIVE RAINFALL ON MONDAY. THIS MARGINAL RISK COVERAGE THEN
SPREADS NORTH TO ALONG US-50 ON TUESDAY. SLOW MOVING STORMS MAY
PRODUCE HEAVY RAINFALL LEADING TO POSSIBLE LOCALIZED FLASH
FLOODING. PLEASE CLEAR DRAINS NOW IF YOU CAN TO HELP PREVENT
POSSIBLE PONDING ESPECIALLY IN URBAN AREAS. AREA RIVERS AND
STREAMS COULD SEE SOME RISES AND INCREASED FLOWS WITH THIS
INCREASED RAINFALL, BUT RIVERS REACHING FLOOD STAGE IS CURRENTLY
NOT FORECAST. -078
REV WATCHES/WARNINGS/ADVISORIES
NV...FLOOD WATCH FROM 2 PM PDT THIS AFTERNOON THROUGH THIS EVENING
NVZ001.
CA...FLOOD WATCH FROM 2 PM PDT THIS AFTERNOON THROUGH THIS EVENING
CAZ073.
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