084
NGUS86 KRSA 271430
HCMRSA
HYDROMETEOROLOGICAL COORDINATION MESSAGE
NATIONAL WEATHER SERVICE / CALIFORNIA-NEVADA RFC / SACRAMENTO CA
730 AM PDT THU AUG 27 2026
...COMBINATION OF OFFSHORE TROPICAL MOISTURE AND MONSOON MOISTURE
TO BRING PERIODS OF SHOWERS AND THUNDERSTORMS TO THE REGION...
...WIDESPREAD COOLING STARTING TOMORROW WITH BELOW NORMAL
TEMPERATURES EXPECTED THROUGH MID NEXT WEEK...
METEOROLOGICAL CONDITIONS (THU AM - WED AM)
REMNANT TROPICAL MOISTURE FROM ISELLE APPROACHES THE COAST, DRAWN IN
BETWEEN TROUGHING OFFSHORE OF THE PACNW/NRN CA AND A STRONG AREA OF
HIGH PRESSURE OVER THE FOUR CORNERS/TX. CURRENT RADAR AND LIGHTNING
DETECTION SHOW SOME RETURNS APPROACHING THE SRN CA COAST WITH
SEVERAL FLASHES/STRIKES. UNCLEAR HOW MUCH IF ANY OF THIS PRECIP WILL
ACTUALLY REACH THE SURFACE. ALTHOUGH TPW IMAGERY SHOWS 1" PW OF
MOISTURE ALONG THE ENTIRE SOUTHERN/CENTRAL CA COASTS, LOOKING AT THE
MORNING 12Z SOUNDINGS SHOWS A PRETTY DECENT DRY LAYER FROM THE
SURFACE UP TO ABOUT 700 MB AT VBG AND NKX. OFFICIAL FORECAST FOR
THIS MORNING HAS SOME SCATTERED FEW HUNDREDTHS. MODELS DO SHOW SOME
SHOWERS POTENTIALLY DEVELOPING OVER THE SOUTHERN SIERRA STARTING
THIS AFTERNOON. THE BULK OF THE MOISTURE IS EXPECTED TO MOVE THROUGH
CENTRAL CA AND NV TOMORROW INTO SATURDAY. THIS SHOULD RESULT IN
SHOWERS AND POSSIBLY THUNDERSTORMS OVER THE SIERRA AND EASTWARD INTO
NRN/CNTRL NV. A FEW SHOWERS MAY MAKE IT INTO THE VALLEY, BUT NOTHING
SUBSTANTIAL. THE VAST MAJORITY OF THE PRECIP SHOULD BE OVER THE
SIERRA AND EASTWARD INTO NV. MODELS THEN HAVE THE BACK END OF THE
MOISTURE PULLING OUT OF CA OVERNIGHT FRIDAY WITH LINGERING SHOWERS
OVER NV ON SATURDAY.
IN ADDITION TO THIS APPROACHING TROPICAL MOISTURE,
CONTINUED MONSOON MOISTURE ROTATING INTO SE CA AND SRN/ERN NV IS
EXPECTED TO BRING SCATTERED SHOWERS AND THUNDERSTORMS THIS
AFTERNOON/EVENING AND CONTINUING EACH DAY THROUGH SATURDAY BEFORE
DRIER AIR BEGINS TO MOVE IN ON SUNDAY. THE CURRENT PATTERN SHOULD
PRODUCE A LITTLE COOLING COMPARED TO YESTERDAY WITH NEAR NORMAL
TEMPERATURES OUTSIDE OF SOUTHERN CA AND ERN/NRN NV. EXPECT MORE
NOTABLE COOLING TOMORROW AND OVER THE WEEKEND AS AN UPPER LOW
DESCENDS INTO THE PACNW FROM THE BC COAST AND EXPANDS TROUGHING
FURTHER INTO CA. ONCE THAT LOW MOVES OUT, ANOTHER IS EXPECTED TO
QUICKLY TAKE ITS PLACE KEEPING BELOW NORMAL TEMPERATURES AROUND
THROUGH AT LEAST MID NEXT WEEK.
ANOTHER ROUND OF TROPICAL MOISTURE IS THEN ON TAP EARLY NEXT WEEK
BEING BROUGHT IN THIS TIME TO SOUTHERN CA. THERE IS A GOOD DEAL OF
UNCERTAINTY AT THIS POINT ON HOW MUCH PRECIP THIS MAY GENERATE. THE
OFFICIAL FORECAST RIGHT NOW FOR TUESDAY INTO WEDNESDAY SHOWS UP TO
0.10-0.25" OVER COASTAL SRN CA AND LESSER AMOUNTS FURTHER INLAND.
THAT DRIER AIR MOVING IN SUNDAY IS EXPECTED TO PREVENT THE TROPICAL
MOISTURE FROM GETTING TOO FAR NORTHWARD, BUT HOW FAR IT DOES GET IS
ANOTHER POINT OF CONTENTION AMONGST THE ENSEMBLES. THE "DET" NBM IS
MUCH MORE WIDESPREAD WITH THE PRECIP SOME OF WHICH IS ABOVE EVEN THE
90TH PERCENTILE WHILE THE 50TH REMAINS BONE DRY. MORE THAN HALF OF
THE ENSEMBLE MEMBERS OF BOTH THE GEFS AND ECMWF ARE DRY OVER LA
WHILE THE WETTER MEMBERS SHOW OVER 1.50" IN A 24 HR PERIOD. LOOKING
AT THE 24 HR QPF CLUSTERS ENDING 00Z THURSDAY, THERE IS A RANGE OF
QPF OF 0" TO 3" OVER PARTS OF COASTAL SRN CA. THE WETTEST CLUSTER IS
ONLY ABOUT 4% OF THE ECMWF AND 15% OF THE CMC WITH NONE OF THE GEFS
MEMBERS GOING THAT HIGH. THERE IS ALSO DISAGREEMENT ON WHERE THE
PRECIP GOES. THE WETTER CLUSTER 3 STOPS AT SOUTHERN MONTEREY COUNTY
WITH SHOWERS DOWN TO SAN DIEGO WHILE CLUSTER 2 IS SHIFTED NORTH
CENTERED OVER MONTEREY COUNTY WITH NOTHING SOUTH OF LA. CLUSTER 1,
WHICH CONTAINS OVER 75% OF THE OVERALL ENSEMBLES IS DRY. BOTTOM
LINE, A LOT OF UNCERTAINTY IN THE FORECAST FOR DAY 6. WENT WITH A
BLEND OF WPC AND THE DET NBM WHILE TRIMMING BACK THE NORTHERN EXTENT
OF PRECIP BASED ON LOOKING AT THE OTHER DET MODELS AND THE PREDICTED
LOCATION OF THAT TROPICAL MOISTURE. THE RESULT IS GENERALLY LESS
THAN 0.10" WITH 0.10-0.25" OVER LA COUNTY AND SHOWERS CUT OFF AROUND
POINT CONCEPTION.
TO SUMMARIZE, A COMBINATION OF TROPICAL MOISTURE FROM THE EASTERN
PACIFIC AND MONSOONAL MOISTURE FROM THE DESERT SOUTHWEST WILL RESULT
IN PERIODS OF SHOWERS AND THUNDERSTORMS OVER PARTS OF THE REGION
THROUGH MID NEXT WEEK. CONTINUED LOWS DROPPING IN FROM THE NORTHWEST
WILL BRING WIDESPREAD BELOW NORMAL TEMPERATURES STARTING TOMORROW.
THE QPF IN THE FIRST 24 HRS WAS A BLEND OF THE NBM/WPC AND THE WEST
WRF AND BEYOND THAT WAS GENERALLY WPC AND THE ECMWF. QPF FOR THE
NEXT 6 DAYS: A FEW HUNDREDTHS TO 0.25" NRN SIERRA, 0.25-1"
CENTRAL/SOUTHERN SIERRA, 0.10-0.75" CENTRAL/NRN NV, A FEW HUNDREDTHS
TO 0.25" COASTAL SRN CA AND 0.10" OR LESS FOR INTERIOR SRN CA.
FREEZING LEVELS 13-16.5 KFT THROUGH THE WEEKEND WITH SOME
FLUCTUATION LOWERING EARLY NEXT WEEK TO 10-15 KFT.
PLEASE NOTE: THIS PRODUCT MAY NOT BE ROUTINELY UPDATED.
PLEASE REFER TO THE FOLLOWING PRODUCT ISSUED BY THE CNRFC
WWW.CNRFC.NOAA.GOV/DAILY-BRIEFING FOR A GRAPHICAL SUMMARY OF
WEATHER AND HYDROLOGIC CONDITIONS.
QPF GRAPHICS ARE AVAILABLE AT WWW.CNRFC.NOAA.GOV/QPF.PHP
*********************** CONTACT INFORMATION ************************
CNRFC OFFICE HOURS PHONE: 1 (916) 979-3056 EXTENSION 338
AFTER-HOURS CALLING SERVICE: 1 (800) 218-0858
LEAVE NAME...OFFICE...AND PHONE NUMBER
AS
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