585
AGUS76 KRSA 202103
HMDRSA
HYDROMETEOROLOGICAL DISCUSSION
NATIONAL WEATHER SERVICE / CALIFORNIA NEVADA RFC / SACRAMENTO CA
105 PM PST WED NOV 20 2024
..HEAVY PRECIP EVENT UNDERWAY FOR NORTHERN CA LASTING INTO FRI
..COOLER WITH CHANCES FOR PRECIP SATURDAY INTO EARLY NEXT WEEK
METEOROLOGICAL CONDITIONS (SHORT TERM: WED PM - SAT AM)
PRECIP CONTINUES IN EARNEST ACROSS NORTHERN CA AS THE DEEP MOISTURE
PLUME INTERSECTS THE COAST WITH PW VALUES AT OR JUST OVER 1.00-INCH
TRANSPORTING EFFICIENTLY INLAND UNDER BROAD SOUTHWEST ONSHORE FLOW.
AUTOMATED GAUGES OVER THE PAST 12 HOURS SHOW THE GREATEST AMOUNTS
FROM THE EEL RIVER BASIN DOWN THROUGH THE RUSSIAN RIVER BASIN AND
THEN INLAND OVER THE SHASTA LAKE DRAINAGE WITH ANYWHERE FROM 1.50-
TO 3.00-INCHES AND EVEN A FEW LOCALIZED AMOUNTS AT 4.00-INCHES. THE
PATTERN WILL BE SLOW TO EVOLVE OVER THE NEXT 48 HOURS LEAVING
NORTHERN CA THE FOCUS FOR MODERATE TO HEAVY PRECIP. DEEP TROFFING
WILL CONTINUE OVER THE NORTHEAST PACIFIC WITH THE UPR JET NOSING
TOWARD THE PACIFIC NORTHWEST...ROTATING INDIVIDUAL DISTURBANCES
TOWARD THE COAST THIS WILL KEEP THE REGION IN THE WARM SECTOR OF
THE SYSTEM...ALLOWING FREEZING LEVELS TO INCREASE TO BETWEEN 8000-
AND 10000-FEET ACROSS NORTHERN CA...PEAKING LATER THURSDAY...BEFORE
DROPPING WITH THE FRONTAL PASSAGE ON FRIDAY. THE PW PLUME WILL
MEANDER ALONG THE NORTH COAST OVER THE NEXT COUPLE DAYS USHERING THE
HIGH MOISTURE CONTENT AIR INLAND THROUGH FRIDAY MORNING UNDER
SOUTHWEST ONSHORE FLOW FOR IDEAL OROGRAPHICS...BEFORE THE COLD FRONT
STARTS TO SHIFT ACROSS THE REGION FROM NORTHWEST TO
SOUTHEAST...FINALLY SHUNTING THE MOISTURE PLUME ACROSS CENTRAL AND
SOUTHERN CA. THIS WILL BRING A GRADUAL DECREASE IN PRECIP AND SHIFT
MODERATE AMOUNTS FINALLY DOWN ACROSS CENTRAL CA. AFTERNOON UPDATE
INCORPORATES THE LATEST WPC QPF AND 20/19Z NBM WITH SOME MANUAL
EDITS TO MATCH GAUGE TRENDS IN THE SHORT TERM.
3 DAY TOTALS STILL SHOW 5.00- TO 10.00-INCHES ACROSS NORTHERN CA
HIGHER TERRAIN WITH LOCALIZED AMOUNTS APPROACHING 15.00-INCHES. FOR
THE SACRAMENTO VALLEY...A RANGE OF 3.00- TO 4.00-INCHES ACROSS THE
SOUTHERN AREAS NEAR SACRAMENTO TO 7.00- TO 8.00-INCHES NEAR REDDING
ARE STILL LOOKING SOLID.
METEOROLOGICAL CONDITIONS (LONG TERM: SAT AM - TUE AM)
PRECIP AMOUNTS GENERALLY DECREASED A LITTLE IN THE AFTERNOON
FORECAST EXCEPT INCREASED AMOUNTS (AROUND A QUARTER OF AN INCH OR
LESS) ALONG THE CENTRAL CA COAST AND INTO THE SRN SIERRA AND
TRANSVERSE RANGE SUNDAY AFTERNOON INTO MONDAY AFTERNOON. ALTHOUGH
THERE IS A LOT OF UNCERTAINTY IN AMOUNTS AND LOCATIONS OF HIGHEST
PRECIP AMOUNTS DUE TO VARIABILITY IN DETAILS OF MODELS AND IN THE
ENSEMBLE MEMBERS.
MAIN LOW PRESSURE SYSTEM OFF THE B.C. COAST WITH ASSOCIATED COLD
FRONT MOVING THROUGH THE REGION AND A TROUGH EXTENDING INTO THE
EASTERN PACIFIC WITH WEAKER LOWS TO THE SOUTHWEST OF MAIN LOW ON
SATURDAY. SEVERAL WEAK DISTURBANCES MOVES THROUGH THE BASE OF THE
TROUGH AND INTO CA OVER THE WEEKEND. THE MAIN LOW HEADS SOUTH OFF
THE PAC NW/ NRN CA COAST ON MONDAY. MOISTURE PLUME AIMED AROUND
POINT CONCEPTION AND SOUTH ALONG SRN CA COAST (PW ABOUT 1.1 INCHES
ALONG SRN CA COAST) FOR SATURDAY THEN STRETCHES NORTH UP ALONG THE
CENTRAL CA COAST AND INTO SJ VALLEY ON SUNDAY THEN BACK DOWN TO SRN
CA COAST SUNDAY NIGHT INTO MONDAY AND POSSIBLY A FINGER REACHING OUT
INTO THE BAY AREA MONDAY NIGHT INTO TUESDAY. SHOWERS ARE POSSIBLE
OVER MOST OF THE REGION (EXCEPT FAR SE CA) SATURDAY INTO MONDAY. THE
HIGHEST PRECIP AMOUNTS ARE EXPECTED OVER THE SIERRA WITH GENERALLY
0.75-1.5 INCHES ON SATURDAY AND AGAIN ON SUNDAY AND 0.5-1.25 INCHES
ALONG THE CENTRAL CA COAST AND INTO THE TRANSVERSE MTNS ON SUNDAY
THEN SHIFTING NORTH TO THE NORTHERN CA COAST AND SHASTA BASIN AND
THE NRN SIERRA WITH 0.75-1.5 INCHES ON MONDAY. ABOUT A THIRD OF THE
ENSEMBLE MEMBERS (32% IN CLUSTER 2) SHOW AMOUNTS UP TO AROUND 3
INCHES OVER THE SIERRA AND UP TO 1.5 INCHES ALONG THE CENTRAL CA
COAST ON THE 24 HOUR QPF 50TH PERCENTILE ENDING 12Z SUNDAY. THE
TRANSVERSE RANGE (CURRENTLY FORECAST 0.5-1 INCH) MAY GET HIGHER
AMOUNTS SUNDAY WITH SOUTHERLY FLOW. ALMOST A QUARTER OF THE
ENSEMBLE MEMBERS SHOW UP TO 2 INCHES OVER THE TRANSVERSE RANGE AND
UP 3 INCHES ALONG THE SIERRA ON SUNDAY ON THE 24 HOUR QPF 50TH
PERCENTILE ENDING 12Z MONDAY. ALTHOUGH 35% OF THE MEMBERS (CLUSTER
1) SHOW MOST OF THE PRECIP STAYING AROUND I-80 AND NORTH WITH 1-2
INCHES ALONG NRN CA COAST AND INTO SHASTA BASIN. QUITE A BIT OF
UNCERTAINTY ON MONDAY WITH PRECIPITATION AMOUNTS AND LOCATIONS
(ESPECIALLY WITH SRN EXTENT OF PRECIP). THE 24 HR QPF 50TH
PERCENTILE CLUSTERS ENDING 12Z TUESDAY SHOW UP TO 3-6 INCHES OVER
NRN CA COAST (CAPE MENDO TO RUSSIAN BASIN AND INTO SHASTA BASIN AND
NRN SIERRA ON 3% OF THE TOTAL ENSEMBLE MEMBERS (COMPOSED ONLY OF 6%
OF EC MEMBERS THEN ABOUT A QUARTER OF MEMBERS (24% TOTAL- CANADIAN
25% GFS 17% AND EC 28%) HAVE AMOUNTS UP TO 2 INCHES ALONG CENTRAL CA
COAST AND UP TO 3 INCHES IN SRN SIERRA.
FREEZING LEVELS GENERALLY DROP TO AROUND 3500-4500 FT NEAR THE ORCA
BORDER AND AROUND 4000-6000 FT FOR THE NRN SIERRA AND AND 5000-7000
FT FOR THE CENTRAL SIERRA AND 7000-9000 FT FOR SOUTHERN SIERRA AND
10,000 FT AND HIGHER FOR SRN CA ON SATURDAY MORNING AND DROP DOWN TO
AROUND 5500-7500 FT IN THE SRN SIERRA AND 7000-10,000 FT OVER SRN CA
SATURDAY AFTERNOON/EVENING. FREEZING LEVELS GENERALLY FLUCTUATE
AROUND 4000-5000 FT NEAR THE ORCA BORDER AND 5000-6500 FT IN NRN
SIERRA AND 5500-8000 FT OVER CENTRAL AND SRN SIERRA AND 9000-11,000
FT OVER SRN CA SUNDAY AFTERNOON INTO MONDAY.
QPF GRAPHICS ARE AVAILABLE AT WWW.CNRFC.NOAA.GOV/QPF.PHP
KOZLOWSKI/OSBORNE
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