609
NGUS86 KRSA 201402
HCMRSA
HYDROMETEOROLOGICAL COORDINATION MESSAGE
NATIONAL WEATHER SERVICE / CALIFORNIA NEVADA RFC / SACRAMENTO CA
700 AM PDT MON OCT 20 2025
...MOSTLY DRY CONDITIONS THROUGH THURS, ASIDE FROM SCATTERED
SHOWERS/T-STORMS OVER THE SRN SIERRA/NV WEDS AS A LOW MOVES
THROUGH...
...MORE WIDESPREAD PRECIP EXPECTED FRI/SAT ACROSS NRN CA AS TROPICAL
MOISTURE IS STEERED TOWARDS THE WEST COAST...
METEOROLOGICAL CONDITIONS (MON AM - SUN AM)
AN UPPER LOW IS CURRENTLY ROTATING OFFSHORE OF SOCAL OUT TO THE
SOUTHWEST WHILE A RIDGE RESIDES OVER THE PACNW/NRN CA. DRY
CONDITIONS THE NEXT COUPLE OF DAYS AS THIS PATTERN PERSISTS. THE
OFFSHORE LOW WILL SLOWLY APPROACH THE COAST DURING THIS TIME MOVING
INLAND AROUND POINT CONCEPTION ON WEDNESDAY. AS THE LOW TRAVELS
ACROSS SRN CA IT MAY DROP A FEW SHOWERS AND POTENTIALLY
THUNDERSTORMS, PARTICULARLY ACROSS THE SOUTHERN SIERRA AND EASTWARD
INTO NV.
DRY CONDITIONS ON THURSDAY AS A LARGE UPPER LOW TRAVERSES THE GULF
OF ALASKA DRAWING IN SOME TROPICAL MOISTURE THAT WILL BE HEADED FOR
THE WEST COAST. MODELS HAVE THIS MOISTURE WRAPPING AROUND A COLD
FRONT APPROACHING THE PACNW INTO FRIDAY WITH THE TAIL OF THIS FRONT
IMPACTING NORTHERN CA. THERE ARE SOME TIMING DIFFERENCES BETWEEN THE
MODELS AT THE MOMENT WITH THE ECMWF ABOUT 6 HRS OR SO AHEAD OF THE
GFS ON THE ARRIVAL OF THE FRONT. THE OFFICIAL FORECAST HAS SHOWERS
REACHING THE NORTH COAST EARLY FRIDAY MORNING SPREADING INLAND INTO
SHASTA BY MID MORNING/EARLY AFTERNOON. TROUGHING FROM THE UPPER LOW
WILL ALSO DIG INTO NRN CA DURING THIS TIME ALLOWING LIGHTER SHOWERS
TO SPREAD INTO THE BAY AREA LATER IN THE DAY.
AFTER THE FRONT MOVES THROUGH AND WEAKENS EARLY SATURDAY, A MORE
DIRECT STREAM OF TROPICAL MOISTURE IS THEN SET TO APPROACH DIRECTED
BY THE UPPER LOW IN THE GULF AND HIGH PRESSURE TO THE SOUTH WHILE
TRAVELING WITH SEVERAL EMBEDDED DISTURBANCES IN THE OVERALL FLOW.
THIS WILL RESULT IN ADDITIONAL PRECIPITATION THE REST OF THE PERIOD,
THOUGH THERE IS UNCERTAINTY AS TO AMOUNTS AND LOCATION. MODELS HAVE
BEEN TRENDING FURTHER NORTHWARD LIMITING IMPACTS FOR OUR REGION TO
NRN CA. THE ECMWF DET AND ENSEMBLES ARE CARRYING PRECIP FURTHER
SOUTH THAN THE EITHER THE GFS OR CMC. LOOKING AT THE QPF CLUSTERS,
ABOUT 70% OF THE ECMWF ENSEMBLE MEMBERS SHOW SHOWERS REACHING THE
CENTRAL SIERRA AND THE SF PENINSULA ALONG WITH 5% OF THE CMC AND 27%
OF THE GFS. THE REST ARE DRY NORTH OF THE GOLDEN GATE. THE OFFICIAL
FORECAST WAS A BLEND OF MORNING WPC GUIDANCE AND THE NBM WHICH DOES
SPREAD PRECIP A BIT FURTHER SOUTH FOR NOW. THIS WILL LIKELY CHANGE
IN THE COMING DAYS AS MODELS HOPEFULLY COME CLOSER TO A CONSENSUS.
SPREAD IN THE 24 HR QPF AMONGST THE ENSEMBLE MEMBERS IS PRETTY HIGH
ALONG THE SOUTHERN EDGE OF THE PRECIP, FOR EXAMPLE AT TAHOE AIRPORT
ENDING 12Z SUNDAY THE AIFS OUT OF THE ECMWF SHOWS TOTALS ANYWHERE
FROM 0 TO 2.50". THE GFS IS EVEN MORE EXTREME GOING UP TO OVER 3" ON
THE UPPER END. ALL THIS TO SAY THERE IS STILL QUITE A BIT OF
UNCERTAINTY IN THE FORECAST PARTICULARLY FOR THE WEEKEND.
THE MAJORITY OF THE QPF IS EXPECTED IN THE EXTENDED WITH ONLY ABOUT
0.10-0.50" IN THE NEAR TERM FOR THE SOUTHERN SIERRA ON WEDNESDAY AS
THAT LOW MOVES INLAND. LESSER AMOUNTS ACROSS THE REST OF NV AND
SCATTERED SHOWERS FOR SRN CA. HIGHER AMOUNTS POSSIBLE UNDER ANY
THUNDERSTORMS. FOR FRIDAY/SATURDAY EXPECTING THE HIGHEST AMOUNTS
ALONG THE NORTH COAST, PARTICULARLY OVER THE SMITH BASIN TAPERING
OFF INTO SHASTA AND THE NRN SIERRA. QPF 12Z FRI-12Z SUN: 1.50-2.50"
NORTH COAST (2.50-4" SMITH BASIN), 1-2" SHASTA, 0.75-1.50" NORTHERN
SIERRA, 0.10-0.75" CENTRAL SIERRA AND THE REST OF NRN CA, 0.25-0.75"
NORTH BAY, 0.10-0.30" AROUND THE BAY AREA TO THE SANTA CRUZ
MOUNTAINS, AND A FEW HUNDREDTHS TO 0.25" FOR THE SOUTHERN SIERRA.
FREEZING LEVELS TO START FRIDAY STILL NORTH OF 12 KFT FOR MOST OF
THE REGION LOWERING INTO SATURDAY TO 5.5-9.5 KFT NORTH OF I-80 AND
9.5-13 KFT FROM I-80 TO THE SOUTHERN SIERRA. LOWER LEVELS WILL
SPREAD A BIT FURTHER SOUTH SATURDAY MORNING BEFORE QUICKLY LEVELING
OFF AT 6.5-9.5 KFT NORTH OF I-80 THE REST OF THE WEEKEND.
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
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