123
NGUS86 KRSA 211427
HCMRSA
HYDROMETEOROLOGICAL COORDINATION MESSAGE
NATIONAL WEATHER SERVICE / CALIFORNIA-NEVADA RFC / SACRAMENTO CA
725 AM PDT WED OCT 21 2026
...COOLER TEMPS ALONG WITH SHOWERS AND THUNDERSTORMS
TODAY/TOMORROW AS A LOW MOVES THROUGH...
...LINGERING SHOWERS OVER THE SIERRA INTO NV ON FRIDAY WITH DRY
CONDITIONS THEN EXPECTED FOR MOST AREAS OVER THE WEEKEND...
METEOROLOGICAL CONDITIONS (WED AM - TUE AM)
AN UPPER LOW CURRENTLY SITS OFFSHORE OF THE CENTRAL COAST ROTATING
SHOWERS AND THUNDERSTORMS INTO CA. LIGHTNING DETECTION SHOWS
ACTIVITY NORTH OF I-80 AND ALONG I-5 WITH NUMEROUS ADDITIONAL
STRIKES OVER THE DESERT SOUTHWEST AND OFFSHORE NEAR THE CORE OF THE
LOW. ACCUMULATIONS OVERNIGHT HAVE BEEN RELATIVELY MINIMAL DOWN THE
CA VALLEYS AT 0.10" OR LESS WITH UP TO 0.25" OBSERVED FOR PARTS OF
NV. CURRENT RADAR SHOWS A BAND OF PRECIP HEADED FOR SRN CA. EXPECT
PRECIP AND THUNDERSTORMS TO CONTINUE TO ROTATE INLAND THROUGHOUT THE
DAY AS THE LOW INCHES CLOSER TO THE COAST. HEAVIER RAINFALL RATES
ARE ANTICIPATED FOR THIS AFTERNOON ALONG COASTAL SRN CA AS 1-1.3" PW
OF MOISTURE FAVORABLY FLOWS INTO THE TRANSVERSE. HREF EXCEEDANCE
PROBABILITIES SHOW A 10-50% CHANCE OF 0.50"+/HR RAIN RATES OVER THE
WESTERN TRANSVERSE AND PORTIONS OF COASTAL SOCAL WITH A 10% CHANCE
OF 2"/HR SHOULD ANY CELLS TRAIN OVER AN AREA. 0.50-1"/HR RATES
REMAIN POSSIBLE FOR PARTS OF THE CENTRAL AND SRN CA COASTS THROUGH
TONIGHT AS THE CORE OF THE LOW BEGINS TO PUSH ONSHORE. MODELS
CONTINUE TO HAVE THIS OCCURRING AROUND POINT CONCEPTION MOVING
THROUGH SRN CA TOMORROW. THE LOW WILL THEN OPEN INTO A TROUGH AS IT
HEADS INTO NV BY THE EVENING WHILE CONTINUING TO PRODUCE SCATTERED
SHOWERS AND THUNDERSTORMS ACROSS THE REGION. THE CORE OF THE SYSTEM
WILL LIFT INTO NRN NV FRIDAY MORNING WITH TROUGHING EXTENDING OUT
OFFSHORE OF BAJA. THE MAIN FOCUS OF PRECIP AT THIS POINT WILL BE
OVER THE SIERRA AND EASTWARD INTO NV, AND IN LESSER AMOUNTS THAN
EXPECTED FOR TODAY/TOMORROW. BOTH THE GFS AND ECMWF NOW SHOW A
SECONDARY LOW FORMING IN THE BASE OF THE TROUGH AXIS FRIDAY
AFTERNOON OVER SRN CA. THIS MAY KEEP A FEW LIGHT SHOWERS LINGERING
OVERNIGHT. UNCERTAINTY REMAINS IN THE FORECAST AS ENSEMBLE SPREAD
CONTINUES TO SHOW A WIDER RANGE OF POSSIBILITIES. SPREAD OVER PARTS
OF COASTAL SRN CA IS STILL AT ABOUT 0.50-2" IN A 24 HR PERIOD FOR
THE CURRENT LOW.
AN UPPER RIDGE WILL BUILD IN BEHIND THE EXITING SYSTEM OVER THE
EASTERN PACIFIC LATE FRIDAY DRIFTING OVERHEAD ON SATURDAY. THIS WILL
KEEP SATURDAY DRY WHILE KICKING OFF SOME WARMING BRINGING AFTERNOON
HIGH TEMPERATURES CLOSER TO SEASONAL NORMALS. THEN ANOTHER UPPER LOW
APPROACHES FROM THE GULF OF ALASKA TOWARDS THE PACNW ON SUNDAY.
THERE IS SOME DISAGREEMENT BETWEEN MODELS AS TO THE TRAJECTORY AND
TIMING OF THIS NEXT LOW. THE ECMWF BRINGS SOME SHOWERS INTO THE
NORTH COAST SUNDAY NIGHT THROUGH MONDAY AS THE SYSTEM PUSHES THROUGH
OR/WA. THE GFS IS A BIT SLOWER ON THE APPROACH AND MORE NORTHERLY
WITH ITS PATH KEEPING PRECIP OUT OF THE AREA ENTIRELY. LOOKING AT
THE ENSEMBLES, SOME SHOW A FRONT FROM THIS SYSTEM (TO VARYING
DEGREES OF STRENGTH) MOVING THROUGH THE NORTH COAST SOME TIME
BETWEEN SATURDAY AFTERNOON AND MONDAY AFTERNOON. SPREAD FOR 24 HR
QPF AT ARCATA IS 0 TO 1" FOR SUNDAY AND MONDAY. CURRENT FORECAST
SHOWS JUST A HANDFUL OF SCATTERED SHOWERS PRODUCING ONLY A FEW
HUNDREDTHS OF AN INCH OVER FAR NRN CA, BUT THIS MAY CHANGE IN THE
COMING DAYS.
QPF WAS AGAIN MAINLY A BLEND OF WPC/NBM, BUT BLENDED IN THE WEST WRF
OVER THE TRANSVERSE AND THE SIERRA FOR SOME TIME FRAMES. OVERALL,
QPF INCREASED FROM YESTERDAY BY 0.10-0.75" NORTH OF LA AND WENT DOWN
SIMILAR AMOUNTS TO THE SOUTH. MAJORITY OF THE PRECIP IS STILL
EXPECTED FOR TODAY/TOMORROW DIMINISHING ON FRIDAY. QPF THROUGH 12Z
SAT: 0.50-1.75" COASTAL SRN CA, 1.50-2.50" TRANSVERSE RANGE, 0.75-2"
SIERRA, 0.25-1" ACROSS MOST OF NV, 0.10-0.75" FOR THE REST OF
NRN/CENTRAL CA, AND 0.10" OR LESS FOR SE CA.
FREEZING LEVELS LOWERING FROM WEST TO EAST TODAY DOWN TO 9-12 KFT
ACROSS CA BY THE LATE AFTERNOON AND 8.5-10.5 KFT MID THURSDAY
MORNING. LEVELS WILL REBOUND WEST TO EAST LATER FRIDAY AS THE SYSTEM
PULLS OUT OF CA WHILE LOWERING OVER NE CA/NW NV DOWN TO 7-8 KFT. THE
REGION SHOULD BE BACK UP TO 11-13 KFT OR SO SUNDAY AFTERNOON.
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
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AFTER-HOURS CALLING SERVICE: 1 (800) 218-0858
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