854
FXUS65 KREV 020819
AFDREV
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RENO NV
119 AM PDT TUE SEP 2 2025
KEY MESSAGES
* THUNDERSTORMS CHANCES RETURN TODAY WITH A RISK FOR FAST MOVING
STORMS WITH MODERATE TO HEAVY RAIN SOUTH OF INTERSTATE 80, AND
DRY LIGHTNING IN NORTHERN WASHOE AND NE CA.
* AREAS OF SMOKE AND HAZE CONTINUE TO LOCALLY IMPACT VISIBILITY
AND AIR QUALITY DUE TO FIRES IN THE SOUTHERN SIERRA.
* THUNDERSTORM CHANCES CONTINUE THROUGH THE END OF THE WEEK, WITH
A POTENTIAL FOR COOLER TEMPERATURES AND INCREASING WINDS THIS
WEEKEND.
DISCUSSION
AFTER A MOSTLY QUIET LABOR DAY WEEKEND ACTIVE WEATHER RETURNS THIS
AFTERNOON TO THE REGION. SMOKE FROM WILDFIRES IN THE REGION MAY
HAVE HINDERED SOME PLANS THIS PAST WEEKEND, ESPECIALLY IF YOU
WERE IN THE EASTERN SIERRA, AND MOST AREAS OF MONO COUNTY. SADLY,
THE SMOKE AND HAZE CONTINUE OVER THE NEXT SEVERAL DAYS IN THE
MORNING AND OVERNIGHT HOURS IN A SIMILAR VICINITY AS WE REMAIN IN
A MOSTLY SOUTHERLY TO SOUTHWESTERLY FLOW.
TALKING ABOUT THAT SOUTHERLY FLOW, IT IS A RESULT OF OUR REGION
BEEN SANDWICHED BETWEEN AN AREA OF HIGH PRESSURE TO OUR EAST AND
A LOW PRESSURE SYSTEM OFF THE NORTHERN CA COAST COMING ONSHORE
TODAY. THIS PATTERN WILL ALLOW MONSOONAL TYPE MOISTURE TO BE
ADVECTED BACK IN WITH PW INCREASING INTO THE 0.6-0.8" RANGE. THE
WARM TEMPERATURES TODAY WILL HELP TO INCREASE INSTABILITY AS THE
LOW PRESSURE MOVES IN RESULTING IN CAPE VALUES IN THE 400-800 J/KG.
THE DYNAMICS OF THE LOW HAVE EMBEDDED SHORTWAVES, DIFFLUENCE ALOFT
AND A MID TO UPPER LEVEL JET STREAK SETTLING OVER THE SIERRA AND
FAR WESTERN NV WHICH WILL FURTHER HELP THE DEVELOPMENT OF STORMS.
THE MAIN DIFFERENCE TO THIS SCENARIO COMPARED TO LAST WEEK IS THE
POSITION OF THE LOW AND THE JET STREAKS RESULTING IN GENERALLY
FAST-MOVING STORMS, ESPECIALLY NORTH OF I-80 WHERE DRY LIGHTNING
WILL BE A CONCERN, (MORE ABOUT THIS IN THE FIRE WEATHER SECTION
BELOW) AND THE REASON FOR THE RED FLAG WARNING. SOUTH, THE STORMS
ARE A TINY BIT SLOWER AND THE MAIN CONCERN WILL BE BRIEF PERIODS
OF MODERATE TO HEAVY RAIN WITH DRY LIGHTNING OUTSIDE OF RAIN
CORES. ISOLATED LOCATIONS IN AREA MOUNTAINS/STEEP TERRAIN MAY HAVE
LONGER PERIODS OF HEAVY RAIN THAT COULD LEAD TO LOCALIZED FLASH
FLOODING AND MUDSLIDES. OTHERWISE, ANY STORM WILL BE CAPABLE OF
PRODUCING GUSTY OUTFLOW WINDS GREATER THAN 45 MPH, FREQUENT
LIGHTNING AND SMALL HAIL. THE MIX NATURE OF THE STORMS TODAY MAY
ALLOW FOR SOME HAIL STONES TO GROW UP TO AN INCH, IF THEY ENTRAIN
ENOUGH DRY AIR ALOFT.
THUNDERSTORM CHANCES WILL CONTINUE FOR THE REST OF THE WORK WEEK.
HOWEVER, THOSE CHANCES WILL BE LOWER COMPARED TO TODAY AS THE
TROUGH MOVES TO THE NORTHEAST AND PUSHES THE MOISTURE AWAY. ON
WEDNESDAY, THE MAIN AREAS OF CONCERN WILL BE THE SIERRA AND THE
EASTERN NV BASIN AND RANGE BASED ON THE HREF. PW WILL CONTINUE TO
DROP THROUGH THE WEEK AND BY FRIDAY WE SHOULD BE BACK BELOW 0.5
INCHES WHICH IS CLOSER TO NORMAL. RAIN AND STORM CHANCES WED-FRI
WILL FLIRT BETWEEN 10-30% EACH DAY.
ENSEMBLE MODELS ARE STARTING TO SHOW A BETTER DRYING TREND FOR
THIS WEEKEND, AS THE NEXT UPPER TROUGH IS UNABLE TO GRAB A DECENT
MOISTURE PLUME DUE TO QUASI-ZONAL FLOW OVER CENTRAL NV/CA. ALTHOUGH
SOME OCCASIONAL SHOWERS AND STORMS MAY BE POSSIBLE ESPECIALLY IN
FAR NORTHERN NV/CA. TEMPERATURES WILL BE COOLING DOWN TO BELOW
AVERAGE AS WINDS START TO INCREASE WITH A SLIGHTLY TIGHTER PRESSURE
GRADIENT. THIS WILL LEAD TO INCREASING WINDS OVER MOUNTAIN RIDGES,
FAR NORTHWEST NV AND NE CA WITH A 30-60% CHANCE OF GUSTS EXCEEDING
30 MPH THIS WEEKEND INTO EARLY NEXT WEEK.
-HC
AVIATION
MOSTLY VFR CONDITIONS CONTINUE THROUGH THE NEXT 24 HOURS WITH
SOME EXCEPTIONS. THE MAIN ONE IS REDUCTIONS IN VIS DUE TO SMOKE,
ESPECIALLY FOR KMMH AND VICINITY IN THE MORNING AND OVERNIGHT
HOURS. THE REST OF THE REGION WILL CONTINUE TO HAVE SLANTWISE VIS
REDUCTIONS FOR THE SAME REASON.
SHOWERS AND THUNDERSTORMS WILL LEAD TO BRIEF PERIODS OF MVFR TO
IFR CONDITIONS MAINLY DUE TO REDUCTIONS IN VIS, BUT ALSO BY LOWER
CIGS AFTER 18Z. MOUNTAIN OBSCURATIONS ARE LIKELY NEAR TSRA IN THE
SIERRA. GUSTY OUTFLOW WINDS WILL ALSO BE A CONCERN WITH STORMS
WITH GUSTS POSSIBLY GREATER THAN 40 KTS.
-HC
FIRE WEATHER
SHOWERS AND THUNDERSTORMS DEVELOP THIS AFTERNOON AS AN UPPER LOW
BRINGS AN INCREASE IN MOISTURE AND INSTABILITY. THE MAIN ACTIVITY
WILL BE OVER THE SIERRA, NE CA AND WESTERN NV. AS STORMS TEND TO
BE MORE ISOLATED FURTHER NORTH, DRY LIGHTNING AND GUSTY OUTFLOW
WINDS BECOMES MORE OF A RISK, LEADING TO A CRITICAL FIRE WEATHER
PATTERN.
FURTHER SOUTH, THE MAIN HAZARDS WILL BE BRIEF PERIODS OF MODERATE
TO HEAVY RAINFALL, SMALL HAIL, GUSTY OUTFLOW WINDS GREATER THAN
45 MPH, AND ISOLATED DRY LIGHTNING ON THE EDGES OF THE HEAVIER
ACTIVITY. ALTHOUGH MOISTURE IS HIGH FOR THIS TIME OF YEAR (90%
PERCENTILE), STORMS ARE EXPECTED TO BE FAST MOVING, SO WE ARE NOT
EXPECTING THE LEVEL OF FLOODING SEEN LAST WEEK.
SHOWER AND STORM ACTIVITY REDUCES FROM WEDNESDAY AND BEYOND TO
AROUND 20% OR LESS, ALTHOUGH THERE IS STILL THE RISK OF DRY
LIGHTNING AND GUSTY OUTFLOW WINDS.
A MORE BREEZY, BUT COOLER PATTERN DEVELOPS THIS WEEKEND WITH THE
APPROACH OF ANOTHER TROUGH. THIS PATTERN COULD LEAD TO ISOLATED
ELEVATED CONCERNS IN MOUNTAIN RIDGES AND OVER NW NV AND NE CA IF
IT WERE TO PERSIST.
-JIM/HC
REV WATCHES/WARNINGS/ADVISORIES
NV...RED FLAG WARNING FROM 1 PM TO 11 PM PDT TUESDAY NVZ458.
CA...RED FLAG WARNING FROM 1 PM TO 11 PM PDT TUESDAY CAZ270-278.
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