396
AGUS76 KRSA 241518
HMDRSA
HYDROMETEOROLOGICAL DISCUSSION
NATIONAL WEATHER SERVICE / CALIFORNIA NEVADA RFC / SACRAMENTO CA
820 AM PDT FRI OCT 24 2025
...WIDESPREAD PRECIP EXPECTED LATER TODAY INTO MONDAY MON ACROSS NRN
CA AS TROPICAL MOISTURE IS FUNNELED INTO THE WEST COAST...
..SLIGHT CHANCE OF T-STORMS SAT AFTERNOON FOR PARTS OF NW CA
METEOROLOGICAL CONDITIONS (FRI AM - THU AM)
DRY CONDITIONS THIS MORNING AS A RIDGE BRIEFLY PASSES THROUGH THE
REGION. JUST BEHIND THE RIDGE LIES A COLD FRONT BEING SENT TOWARDS
THE WEST COAST OFF OF A LARGE UPPER LOW IN THE GULF OF ALASKA. THIS
SYSTEM IS DRAWING IN ABOUT 1-1.50" PW OF TROPICAL MOISTURE.
SATELLITE IMAGERY SHOWS THE SOUTHERN EDGE OF THIS PLUME JUST
NORTHWEST OF THE CA/OR BORDER AS OF 12/13Z. THE FRONT WILL CONTINUE
TO APPROACH THIS MORNING AS TROUGHING ALSO MOVES IN FROM THE
NORTHWEST. EXPECTING SHOWERS FROM THE COLD FRONT TO REACH THE NORTH
COAST SOME TIME THIS AFTERNOON BEFORE SPREADING INLAND IN THE
EVENING/OVERNIGHT TO THE SHASTA/EEL BASINS. HREF 1HR EXCEEDANCE
PROBABILITIES SHOW ABOUT 40-70% CHANCE OF 0.50+"/HR RAIN RATES IN
THE LATE AFTERNOON. BEHIND THE FRONT, ANOTHER SURFACE LOW WILL SPIN
OFF OF THE LARGER SYSTEM IN THE GULF OF ALASKA AND HEAD
NORTHEASTWARD INTO SATURDAY AS WELL. THIS WILL HELP PULL ADDITIONAL
MOISTURE INTO THE AREA THAT IS ALREADY BEING FUNNELED IN BY THE
RIDGE NORTH OF THE HAWAIIAN ISLANDS AND THE GULF LOW. THIS NEXT
SURGE OF PRECIP IS SET TO ARRIVE ALONG THE NORTH COAST SATURDAY
MORNING AS SHOWERS CONTINUE ACROSS MUCH OF THE REST OF NRN CA.
THUNDERSTORMS POSSIBLE FOR PARTS OF NW CA AS WELL ON SATURDAY AS
MODELS SHOW THE AREA UNDER THE LEFT EXIT REGION OF A 120-130+KT JET
STREAK ALONG WITH SOME INSTABILITY. POTENTIAL AGAIN FOR 0.50"+/HR
RAIN RATES.
ANOTHER DISTURBANCE THEN LOOKS TO FORM OFF OF THE MAIN GULF LOW INTO
SUNDAY, SENDING AN ADDITIONAL BURST OF PRECIP INTO THE NORTH COAST
AGAIN RIDING UNDER THE LEFT EXIT REGION OF AN UPPER JET. PRECIP WILL
LIFT NORTHWARD THE REST OF SUNDAY AFTERNOON/EVENING AS HIGHER 500 MB
HEIGHTS ARE PUSHED NORTHWARD. SOME UNCERTAINTY FOR MONDAY AS THE
GFS/ECMWF SHOW ANOTHER CLOSED SURFACE LOW APPROACHING THE WEST
COAST, HOWEVER FOR THE MOMENT, BOTH MODELS SEND THIS SYSTEM AND ITS
PRECIP MOSTLY NORTH OF CA TO DIFFERING DEGREES. THE GFS HAS A MUCH
WEAKER SYSTEM WITH THE CENTER OF THE LOW BOTTOMING OUT AT 1003 MB IN
THE AFTERNOON BEFORE WEAKENING AS IT APPROACHES THE PACNW RESULTING
ONLY SOME RELATIVELY LIGHT SHOWERS OVER THE NORTHERN BORDER INTO THE
SMITH BASIN INTO TUESDAY. THE ECMWF HAS THIS LOW FURTHER NORTHWARD
SPARING THE AREA OF PRECIP FOR MONDAY BUT DEVELOPS A MUCH MORE
ROBUST SURFACE LOW WITH A CENTRAL PRESSURE OF 968 MB BY MID TUESDAY
MORNING. THE ECMWF THEN SENDS PRECIP FROM THIS LOW WRAPPED AROUND A
COLD FRONT INTO THE PACNW WITH SHOWERS REACHING JUST SOUTH OF CAPE
MENDOCINO OVERNIGHT. THE ENSEMBLE CONSENSUS IS DRY FROM SUNDAY
EVENING TO TUESDAY EVENING WITH 80% OF THE MEMBERS FROM THE
GFS/ECMWF/CMC SHOWING MAYBE AN ISOLATED SHOWER OR TWO AT MOST, BUT
THERE IS STILL AT LEAST SOME (20%) CHANCE OF MORE MODERATE AMOUNTS
ALONG THE NORTH COAST DEPENDING ON WHAT HAPPENS WITH THAT LAST
SURFACE LOW. GENERALLY DRY CONDITIONS EXPECTED TUESDAY ONWARD ASIDE
FROM SOME LIGHT SHOWERS POSSIBLE ALONG THE NORTHERN REGIONAL BORDER
INTO THE SMITH BASIN AS ADDITIONAL DISTURBANCES MOVE THROUGH THE
PACNW.
THE MAIN EVENT WILL BE LATER TODAY THROUGH SUNDAY WITH ALL BUT ABOUT
0.10-0.25" OF THE 6 DAY QPF TAKING PLACE BETWEEN 00Z FRI AND 00Z
MONDAY. MODELS HAVE CONTINUED TO TREND DRIER WITH THE PRECIP AMOUNTS
BRINGING DOWN THE STORM TOTAL FORECAST FROM YESTERDAY BY ANOTHER
0.25-1". HIGHEST AMOUNTS STILL EXPECTED OVER THE SMITH BASIN AND
THEN THE NORTH COAST INTO SHASTA. QPF AS FOLLOWS: 1.50-3" NORTH
COAST (3-5" SMITH BASIN), 1.50-2.50" SHASTA, 0.75-2" NORTHERN
SIERRA, 0.25-0.75" CENTRAL SIERRA, 0.50-1.50" FOR THE REST OF NRN CA
NORTH OF SONOMA COUNTY, 0.10-0.75" DOWN THE SACRAMENTO VALLEY INTO
THE NORTH BAY, AND A FEW HUNDREDTHS TO 0.25" FOR THE BAY AREA.
FREEZING LEVELS NORTH OF 12.5 KFT FOR MOST OF THE REGION THIS
MORNING LOWERING INTO SATURDAY TO 6-10.5 KFT NORTH OF I-80 AND 10-
13.5 KFT FROM I-80 TO THE SOUTHERN SIERRA. LOWER LEVELS WILL SPREAD
A BIT FURTHER SOUTH THE REST OF SATURDAY DOWN TO 5-10.5 KFT NORTH OF
I-80 IN THE EVENING AND HOVERING AROUND THERE THROUGH SUNDAY MORNING
BEFORE HIGHER VALUES SPREAD BACK NORTHWARD LATER IN THE DAY UP TO 7-
13 KFT NORTH OF I-80 IN THE EVENING. THIS TREND WILL CONTINUE INTO
MONDAY AS WELL.
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
AS
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