Hydrometeorological Discussion
Issued by NWS California-Nevada RFC

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8
000
AGUS76 KRSA 311609
HMDRSA

DDHHMM
WRKHMD

HYDROMETEOROLOGICAL DISCUSSION
NATIONAL WEATHER SERVICE / CALIFORNIA NEVADA RFC / SACRAMENTO CA
930 AM PDT FRI OCT 31 2014

...WIDESPREAD PRECIP TODAY INTO TOMORROW...
...MOSTLY DRY NEXT WEEK WITH A CHANCE OF PRECIP OVER THE FAR NORTH...

.24 HOUR PRECIPITATION TOTALS (ENDING OCT 31 AT 500 AM PDT)...

THE LEADING EDGE OF A VIGOROUS COLD FRONTAL SYSTEM BEGAN TO MOVE
THROUGH THE NORTH COAST LATE LAST NIGHT...BRINGING PRECIP TO AREAS
FROM THE SMITH BASIN SOUTH TO THE NORTHERN PIECE OF THE RUSSIAN R
BASIN. HIGHEST AMOUNTS WERE TALLIED OVER THE SMITH BASIN...WHERE 1-
1.5" FELL ALONG THE COAST...AND UP TO 1.5-2" OVER HIGHER TERRAIN ON
THE WEST SLOPES OF THE TRINITY MTNS. AMOUNTS FELL OFF SHARPLY
FURTHER EAST INTO THE UPPER KLAMATH...WHERE JUST A FEW TENTHS OF AN
INCH WAS RECORDED. THE EEL R BASIN PICKED UP 0.4-0.8" PRECIP THROUGH
5 AM THIS MORNING...WHILE LESS THAN 0.1" HAD ACCUMULATED OVER THE
RUSSIAN R BASIN. AROUND 0.05-0.15" HAD BEEN MEASURED OVER THE SHASTA
BASIN BY 5 AM AS WELL.


.METEOROLOGICAL CONDITIONS (SHORT TERM: FRI AM - MON AM)...

IMPRESSIVE UPR TROF SITS OFF THE WEST COAST THIS MORNING...WITH THE
AXIS OF THIS SYSTEM ABOUT TO CROSS 130W. THE PRIMARY CIRCULATION
WITH THIS FEATURE IS SPINNING NEAR 47N/132W...WHILE A POTENT VORT
MAX IS DROPPING TOWARD THE BASE OF THE SYSTEM NEAR 40N/134W. THE
ASSOCIATED COLD FRONT HAS MOVED INLAND ACROSS THE PACNW AND IS NOW
CROSSING THE NORTHERN CA COASTAL MOUNTAINS. ALTHOUGH THE PRECIP BAND
ALONG THE COLD FRONT IS FAIRLY NARROW...IT IS MOVING AT A SLOW PACE
INLAND AND THERE IS A DECENT AMOUNT OF AVAILABLE MOISTURE CONVERGING
AHEAD OF THE BOUNDARY. BLENDED TPW IMAGERY SHOWS VALUES JUST OVER
1.00-INCH ALONG THE COAST BETWEEN THE GOLDEN GATE AND CAPE
MENDOCINO...WHILE INLAND AMOUNTS RANGE FROM 0.75- TO 1.00-INCH. THE
GPS-MET IPW SENSORS MATCH UP WELL WITH THE GAGES BETWEEN CHICO AND
SHASTA DAM SHOWING VALUES PEAKING NEAR 1.00-INCH.

AS EXPECTED...SOUTHERLY FLOW AHEAD OF THE COLD FRONT HAS RAMPED UP
WITH GOOD CONVERGENT CONDITIONS DEVELOPING OVER THE SHASTA LAKE
DRAINAGE. SFC WINDS AT RED BLUFF AND CHICO HAVE REACHED BETWEEN 15-
AND 20-KT...WHILE THE KBBX VAD WIND PROFILER (31/1454Z) SHOWS
SOUTHERLY FLOW JUST OFF THE GROUND AT 25-KT. LOOKING AT PRECIP GAGES
SINCE 31/12Z IN THE WESTERN SHASTA LAKE DRAINAGE...TRINITY LAKE AREA
THERE ARE ALREADY SOME AMOUNTS SURPASSING 0.25-INCH.

FOR THE AFTERNOON...THE PRECIP ASSOCIATED WITH THE FRONTAL BAND WILL
MOVE OVER THE UPPER KLAMATH RIVER BASIN SOUTH ACROSS THE EASTERN
PORTION OF THE SHASTA LAKE DRAINAGE...THE SACRAMENTO VALLEY...AND
THE SF BAY AREA. THE 31/06Z GFS IS SHOWING SOME RATHER IMPRESSIVE
AMOUNTS IMBEDDED WITHIN THIS LINE...WHILE THE 31/09Z SREF IS DRIEST.
FOR THIS PERIOD...INCREASED AMOUNTS OVER THE PREVIOUS
FORECAST...ESPECIALLY OVER THE SF BAY AREA. MODELS SHOW THE MOISTURE
PLUME HOLDING TOGETHER RATHER WELL FROM THE SF BAY AREA NNE TO THE
SACRAMENTO AREA WITH PW VALUES NEAR 1.00-INCH.

BY THE EVENING...THE COLD FRONT WILL MOVE INTO WESTERN NEVADA BACK
SOUTH ACROSS THE SOUTHERN SIERRA AND OFFSHORE NEAR PT CONCEPTION.
THE UPR TROF WILL NUDGE CLOSER TO THE COAST WITH A FAIRLY ROBUST
VORT MAX CROSSING PT CONCEPTION. ALL THE MODELS SHOW PRECIP PICKING
UP IN INTENSITY OVER THE SIERRA SOUTH OF LAKE TAHOE...BACK ACROSS
THE SAN JOAQUIN VALLEY AND THE CENTRAL CA COAST. ALSO...ALTHOUGH NOT
PROLONGED...FLOW DOES DEVELOP A BIT OF A SOUTHERLY COMPONENT OVER
THE TRANSVERSE RANGES OF SOUTHERN CA...WHICH WILL ENHANCE THE PRECIP
SLIGHTLY.

DURING THE OVERNIGHT...THE HEAVIEST PRECIP WILL BE FOCUSED OVER THE
SOUTHERN SIERRA FROM ABOUT YOSEMITE NP AND POINTS SOUTH. THIS AREA
SITS IN A REGION OF GOOD CYCLONIC FLOW ALOFT...AND AN APPROX 110-KT
UPR JET STREAK SLICING FROM NEAR PT CONCEPTION TO NEAR DEATH VALLEY
AND NOSING TO EAST-CENTRAL NEVADA. THE MODELS HAVE ALSO BEEN RATHER
PERSISTENT IN DEVELOPING A BAND OF PRECIP OVER WESTERN NEVADA FROM
JUST SOUTH OF RENO NORTH TO THE OREGON BORDER. BACK CLOSER TO THE
COOLEST AIR ASSOCIATED WITH THE UPR TROF...SCATTERED SHOWERS WILL
AFFECT AREAS WELL BEHIND THE COLD FRONT. FOR SOUTHERN CA...PRECIP IS
EXPECTED TO MAKE ITS WAY TO THE US/MEXICO BORDER. THE BEST
OPPORTUNITY FOR THE HEAVIEST PRECIP SOUTH OF PT CONCEPTION WILL BE
BETWEEN SANTA BARBARA AND WESTERN SAN BERNARDINO COUNTY WITH WPC
PROBAILISTIC QPF SHOWING THE LIKELIHOOD OF AT LEAST 0.25-INCH NEAR
75-PERCENT OR HIGHER. STILL THINK TOTALS NEAR PT CONCEPTION WILL END
UP NEAR OR JUST OVER 1.00-INCH...AND THEN TRAIL OFF CLOSER TO 0.25-
TO 0.33-INCH OVER SAN DIEGO COUNTY. THE MODELS HAVE LATCHED ON TO
THIS SYSTEM HOLDING TOGETHER QUITE WELL OVER SOUTHERN CA FOR DAYS
NOW.

INTO SATURDAY...THE UPR TROF WILL MOVE ACROSS NEVADA AND BEGIN TO
LIFT OUT TO THE NE...BUT A RE-INFORCING S/WV TROF ON THE BACKSIDE OF
THE SYSTEM WILL KEEP GENERAL TROFFINESS OVER THE REGION. SHOWERS
WILL CONTINUE WITH THE BEST CONCENTRATION OVER THE SIERRA AND POINTS
EAST (COVERING THE MAJORITY OF NEVADA). OTHER AREAS WILL SEE
DECREASING PRECIP WITH LIGHTER AMOUNTS.

SUNDAY WILL BE A TRANSITION DAY AS THE ELONGATED UPR TROF MOVES OFF
TOWARD THE EAST AND A POSITIVELY TILTED UPR RIDGE NOSES TOWARD THE
PACNW AND NORTHERN CA.


.METEOROLOGICAL CONDITIONS (LONG TERM: MON AM - THU AM)...

THE EXTENDED FORECAST IS FAIRLY QUIET. BY MONDAY...RIDGING REBUILDS
OVER THE AREA AS THE UPPER TROUGH MOVES THROUGH THE ROCKIES...AND
HIGH PRESSURE STRENGTHENS OUT NEAR 25N/135W. MOIST WESTERLY FLOW
DOES CONTINUE OVER THE PACIFIC NORTHWEST MON AND TUES...BRINGING A
SLIGHT CHANCE OF LIGHT PRECIP TO THE UPPER KLAMATH AND POSSIBLY
SMITH BASIN. THE GFS IS MORE AGGRESSIVE WITH THIS...WHILE THE EC
KEEPS THE SOUTHERN EDGE OF PRECIP WELL TO OUR NORTH. BY WEDNESDAY...
THE UPPER JET AGAIN TURNS SOUTHWESTERLY AS AN UPPER LOW DEVELOPS
OVER THE GULF OF ALASKA. THIS PUSHES THE STORM TRACK BACK TOWARDS
THE WA/CANADA BORDER...WHILE A FRONTAL SYSTEM DEVELOPS OFF THE
COAST. THIS SYSTEM WILL AFFECT THE REGION ON THURSDAY AND FRIDAY...
TO VARYING DEGREES DEPENDING ON WHETHER THE CURRENT GFS OR EC
VERIFY.


.HYDROLOGICAL CONDITIONS...

PRECIPITATION FORECAST FOR TODAY AND SATURDAY IS EXPECTED TO PRODUCE
MINOR RISES ON MANY RIVERS AND STREAMS ACROSS MUCH OF CALIFORNIA AND
NEVADA.  ALTHOUGH NOT A GREAT WATER SUPPLY CONTRIBUTOR..THIS
PRECIPITATION EVENT IS ANOTHER IN A SERIES OF WEAK EARLY SEASON
STORM SYSTEMS THAT CONTINUE TO ADD MOISTURE TO BASIN SOIL CONDITIONS.

ALL CALIFORNIA AND NEVADA RIVER STAGES ARE EXPECTED TO REMAIN WELL
BELOW MONITOR LEVELS FOR THE NEXT WEEK.


MORE INFORMATION ON THE CNRFC WEBSITE AT HTTP://WWW.CNRFC.NOAA.GOV

JM/DRK/JM/AM

$$



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.