Hydrometeorological Discussion
Issued by NWS California-Nevada RFC

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AGUS76 KRSA 211615
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HYDROMETEOROLOGICAL DISCUSSION
NATIONAL WEATHER SERVICE / CALIFORNIA NEVADA RFC / SACRAMENTO CA
930 AM PDT TUE OCT 21 2014

...FIRST SYSTEM TO BRING HEAVY PRECIP TO THE NORTH COAST WED-THURS...
...SECOND SYSTEM EXPECTED ACROSS SRN OREGON/NRN CA/CNTRL CA FRI-
SAT...

.24 HOUR PRECIPITATION TOTALS (ENDING OCT 21 AT 500 AM PDT)...

AN UPPER-LEVEL TROUGH AND ASSOCIATED COLD FRONT SWUNG ACROSS NRN
CA/SRN OREGON AND INTO NRN NV DURING THE PERIOD.  HEAVIEST AMOUNTS
WERE NEAR THE SMITH BASINS, WITH AMOUNTS OF 0.6-0.8" NEAR THE COAST
AND 1.4-2.1" JUST INLAND.  0.4-1" WAS REPORTED IN THE LOWER KLAMATH,
WITH GENERALLY 0.3-0.6" IN THE MAD AND EEL BASINS.  AMOUNTS FURTHER
SOUTH WERE AROUND 0.3" OR LESS IN THE RUSSIAN/NAPA BASINS, WITH A
FEW HUNDREDTHS OF AN INCH REPORTED SOUTH TO NEAR MONTEREY BAY.  OVER
INTO THE SACRAMENTO VALLEY, THE SRN PORTION RECEIVED AROUND 0.01"
WITH A FEW HUNDREDTHS TO NEAR 0.1" REPORTED FURTHER NORTH, UP TO
0.2" IN REDDING.  TOTALS AROUND SHASTA LAKE WERE 0.3-0.9" WITH 0.1-
0.5" IN THE UPPER KLAMATH INCLUDING THE SRN OREGON CASCADES.
LOOKING AT THE NRN SIERRA, TOTALS WERE 0.4-0.8" NORTH OF I-80  WITH
A FEW HUNDREDTHS AS FAR SOUTH AS THE STANISLAUS.  EAST-SIDE AMOUNTS
WERE AROUND 0.2" OR LESS, WITH GENERALLY 0.2-0.5" IN NE CA.  A FEW
HUNDREDTHS OF AN INCH FELL ACROSS NRN NV WITH A FEW GAUGES AROUND
0.2-0.3" IN THE FAR NORTH.


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

MOIST WESTERLY FLOW HAS CONTINUED TO BRING SHOWERS TO THE NW CA
COAST OVERNIGHT...AND CONTINUE EARLY THIS MORNING.  THESE...AND A
FEW LINGERING SHOWERS OVER NORTHERN NEVADA...ARE EXPECTED TO COME TO
A CLOSE AS A S/WV RIDGE DEVELOPS LATER THIS MORNING. MEANWHILE...THE
NEXT SYSTEM ON TAP IS A LOW PRESSURE SYSTEM DEEPENING OVER THE GULF
OF ALASKA...CENTERED NEAR 52N/140W. A STRONG UPPER JET WILL HELP
DRIVE THE ASSOCIATED FRONTAL SYSTEM INTO WASHINGTON AND OREGON ON
WEDNESDAY...AND INTO THE NORTH COAST LATE WEDNESDAY NIGHT. THIS
SYSTEM IS FED BY A MOISTURE PLUME WITH A 1.4" CORE AND NEAR 1.2"
AMOUNTS AS IT HITS THE NORTHERN CA COAST. FAVORABLE 50-KT SOUTHWEST
FLOW AT 850-MB WILL ALLOW BRING HEAVY PRECIP TO THE SMITH BASIN
DURING THE OVERNIGHT HOURS...WITH 2-4"+ RAINFALL AMOUNTS POSSIBLE BY
THURSDAY MORNING.

AS THE MOISTURE PLUME SAGS SOUTHWARD THURSDAY MORNING...EXPECT FOCUS
OF PRECIP TO SHIFT INTO THE EEL AND RUSSIAN R BASINS THURS LATE
MORNING AND AFTERNOON...AS WELL AS PUSHING INTO THE SHASTA DRAINING
AND FAR NORTHERN SIERRA FURTHER INLAND. THE FRONT DOES BEGIN TO LOSE
STEAM INTO THURSDAY EVENING AS IT SAGS INTO THE NAPA AND INTO THE SF
BAY...BUT DO EXPECT LIGHT TO MODERATE PRECIP TO CONTINUE THROUGH THE
EVENING.

FREEZING LEVELS THROUGH THIS SYSTEM WILL REMAIN FAIRLY HIGH...ONLY
MANAGING TO DROP TO 8500 FEET OVER THE NORTH COAST BEHIND THE FRONT.
THIS SHOULD KEEP EVERYTHING FALLING AS LIQUID THROUGH THE SHORT
TERM.

DURING THIS TIME ON THURSDAY...THE PARENT LOW IS EXPECTED TO DROP
SOUTH...WITH THE TROUGH MOVING INTO THE WATERS OFF THE NORTHERN CA
COAST AROUND 40N. EXPECT THIS NEXT WAVE OF PRECIP TO MOVE THROUGH ON
FRIDAY.


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

DESPITE SOME MODELS DIFFERENCES IN THE LONG RANGE, MODELS GENERALLY
AGREE ON THE NEXT SYSTEM SPREADING PRECIP ACROSS NW CA/SRN OREGON
FRI AND ACROSS THE REMAINDER OF NRN CA AND POTENTIALLY INTO CNTRL CA
FRI NIGHT THROUGH SAT NIGHT.  AS A STARTING POINT, WE UTILIZED A
BLEND OF THE 06 UTC GFS AND 00 UTC ECMWF, WHICH SHOWED REASONABLE
ENOUGH AGREEMENT DESPITE THE GFS BEING A LITTLE FASTER.  THE ECMWF
ENSEMBLE MEAN LOOKED FAIRLY SIMILAR TO THE DETERMINISTIC RUN, AND
THE GEFS MEAN WAS SLIGHTLY SLOWER THAN THE DETERMINISTIC.

THE HEAVIEST PERIOD IS EXPECTED TO BE ON THE NORTH COAST SOMETIME
NEAR THE FRI EVENING PERIOD WITH THE FRONT MOVING ONTO THE COAST AND
A DECENT SHORTWAVE FOLLOWING CLOSE BEHIND.  OROGRAPHICS DO NOT
APPEAR TO EVER BECOME TOO IDEAL NORTH OF CAPE MENDOCINO WITH H85
FLOW REMAINING MAINLY SLY DESPITE REACHING 45-65 NEAR THE SMITH
BASIN AND 35-45 KTS NEAR CAPE MENDOCINO.  PW VALUES NEAR THE FRONT
TOP OUT JUST OVER 1.3".  DYNAMIC FORCING ALOFT SHOULD MAKE UP FOR
SOME OF THE LACK OF OROGRAPHIC FLOW AND PRODUCE MODERATE TO HEAVY
AMOUNTS FROM AROUND CAPE MENDOCINO NWD.  LOCATIONS SUCH AS THE KING
RANGE NEAR CAPE MENDOCINO SHOULD SEE SOME DECENT OROGRAPHIC
ENHANCEMENT, HOWEVER, WITH THE FAIRLY STRONG SLY FLOW.

PRECIP SHOULD BE MAINLY LIGHT ELSEWHERE AS THE FRONT MOVES INLAND
AND FURTHER SOUTH.  MOST PRECIP SHOULD STAY NORTH OF A LINE FROM THE
CNTRL COAST TO AROUND YOSEMITE, ALTHOUGH THE ECMWF BRINGS LIGHT
AMOUNTS INTO PORTIONS OF SRN CA AND THE REMAINDER OF THE SIERRA
RANGE SAT NIGHT AS A SRN PORTION OF THE TROUGH BREAKS OFF AND MOVES
ACROSS THE REGION.  PORTIONS OF THE SHASTA DRAINAGE COULD SEE
SOMEWHAT ENHANCED AMOUNTS WITH THE SLY FLOW AHEAD OF THE FRONT FRI
NIGHT.  EXPECT DRYING BY LATE IN THE WEEKEND WITH RIDGING BUILDING
INTO THE REGION.

FREEZING LEVELS ARE FORECAST TO START OFF AROUND 10,000 FT OR ABOVE
ON FRI AHEAD OF THE COLD FRONT AND LOWER TO 6000-7000 IN THE FAR
NORTH AND 7000-8000 FT IN THE NRN AND CNTRL SIERRA FOLLOWING FRONTAL
PASSAGE.


.HYDROLOGICAL CONDITIONS...

PRECIPITATION OVER NORTHWEST CALIFORNIA FOR THE PAST 24 HOURS HAS
PRODUCED MINOR RISES IN STAGE ON MANY AREA RIVERS AND STREAMS.

PRECIPITATION FORECAST FOR NORTHERN CALIFORNIA FOR THE NEXT SEVERAL
DAYS IS EXPECTED TO PRODUCE CONTINUED MINOR RISES IN STAGE ON AREA
RIVERS AND STREAMS.

ALL RIVERS AND STREAMS IN THE CNRFC FORECAST AREA ARE CURRENTLY
BELOW...AND ARE EXPECTED TO REMAIN BELOW MONITOR LEVELS THROUGH
SATURDAY.


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

KL/JM/KL/SS

$$



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