Hydrometeorological Discussion
Issued by NWS California-Nevada RFC

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HYDROMETEOROLOGICAL DISCUSSION
NATIONAL WEATHER SERVICE / CALIFORNIA NEVADA RFC / SACRAMENTO CA
930 AM PST TUE DEC 23 2014

...FAST-MOVING AND COOLER STORM EXPECTED WED INTO WED NIGHT DRYING
THU...
...NEXT WEAK SYSTEM IN THE FAR NORTH EXPECTED THIS WEEKEND...

.24 HOUR PRECIPITATION TOTALS (ENDING DEC 23 AT 400 AM PST)...

WAA/ISENTROPIC LIFT TYPE PRECIP BROUGHT LIGHT PRECIP TO AREAS NEAR
THE CA/ORE BORDER AND INLAND OVER FAR NORTHERN NEV. TOTALS WERE
GENERALLY NEAR 0.10-INCH OR LESS WITH A FEW HIGHER TOTALS OVER NE
NEVADA BETWEEN 0.25- AND 0.50-INCH.


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

RIDGING OVER THE WEST COAST IS PROVIDING DRY CONDITIONS ACROSS THE
REGION TODAY.  A BROAD TROUGH NOW NEAR 150W IS FORECAST TO SHARPEN
AND MOVE INTO NW CA ON WED.  PW VALUES ARE EXPECTED TO APPROACH 1"
NEAR A COLD FRONT.  SW-W FLOW AROUND 30 KTS AT H85 AHEAD OF THE
FRONT IS EXPECTED TO QUICKLY GIVE WAY TO STRONG NWLY FLOW BY WED
AFTERNOON BEHIND THE FRONT.  EXPECT PRECIP TO QUICKLY SPREAD ACROSS
NRN/CNTRL CA AND SRN OREGON WED MORNING/AFTERNOON AND ACROSS NRN NV
BY WED EVENING.  MUCH OF THE PRECIPITATION IS EXPECTED TO BE DRIVEN
BY STRONG DYNAMICS AND TOTALS SHOULD BE MORE UNIFORM THAN
CLIMATOLOGY WOULD INDICATE.

THE FRONT SHOULD PUSH INTO SRN CA BY WED NIGHT, WITH THE SRN SIERRA
AND EVEN SOME SRN CA HIGHER TERRAIN EXPECTED TO RECEIVE SOME LIGHT
SHOWERS.  THE TROUGH IS FORECAST TO SLOWLY MOVE EAST ON THU, WITH
THE REGION REMAINING UNDER NLY OR NWLY FLOW ALOFT UNDER AN UPPER
JET.  EXPECT A FEW LIGHT SHOWERS TO LINGER OVER THE SRN OREGON
CASCADES AND NE NV INTO THU NIGHT.  DESPITE SOME TIMING DIFFERENCES
WITH THE ONSET OF THE SYSTEM, MODEL AGREEMENT IS REASONABLY GOOD
OVERALL REGARDING TIMING OF THE SYSTEM, WITH THE HIGHER-RES MODELS
WETTER ESPECIALLY IN THE SIERRA.  OUR FORECAST IS IN BETWEEN THE
WETTER AND DRIER SOLNS IN THE SIERRA.

GIVEN THE TRAJECTORY OF THE SYSTEM MOVING IN FROM THE WNW, FREEZING
LEVELS ARE EXPECTED TO FALL FAIRLY DRAMATICALLY WITH THE SYSTEM,
STARTING AROUND 10,000 FT OR ABOVE NEAR THE ONSET OF PRECIP AND
FALLING TO 3000-5000 FT IN NRN/CNTRL CA/NV AND SRN OREGON AND
REMAINING 8000 FT AND ABOVE IN SRN CA.  OVERALL OUR FORECAST IS
SIMILAR TO WPC`S, ALTHOUGH THEIRS IS WETTER IN THE SMITH FOR WED
AFTERNOON.


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

THE REGION WILL BE SITTING BETWEEN AN UPR RIDGE UPSTREAM ALONG 135W
AND AN EXITING UPR TROF ALIGNED OVER UTAH AND ARIZONA. THIS WILL
GENERATE DRY NORTHERLY FLOW ACROSS THE REGION ON FRIDAY. AVAILABLE
MOISTURE WILL BE BELOW NORMAL WITH PW VALUES RANGING SOMEWHERE
BETWEEN 0.10- AND 0.25-INCH. THE ONLY OPPORTUNITY FOR PRECIP WILL BE
ACROSS FAR EASTERN NEV CLOSEST TO THE CORE OF THE UPR TROF.

THE UPR TROF WILL MOVE OFF TOWARD THE EAST ON SATURDAY WITH A WEAK
S/WV RIDGE MOVING ACROSS THE REGION FROM NW TO SE. THE NEXT
CONTINENTAL POLAR SYSTEM WILL DIVE IN FROM THE NORTH AND IS EXPECTED
TO IMPACT THE FAR NORTHERN AREAS ON SUNDAY NEAR THE CA/ORE BORDER
AND PORTIONS OF NORTHERN NEV. THERE LOOKS TO BE A SLIGHT UPTICK OF
MOISTURE AHEAD OF THE SYSTEM THAT WILL GENERATE SOME LIGHT PRECIP
WITH THE BEST CHANCES EAST OF THE SIERRA CREST.

BEYOND THE FORECAST PERIOD...THIS SYSTEM WILL DIVE THROUGH THE GREAT
BASIN. LIGHT PRECIP WILL MOVE OVER THE CREST OF THE SIERRA AND
POINTS EAST. BEHIND THE COLD FRONT...EXTREMELY DRY AIR WILL MOVE
ACROSS THE REGION WITH PW VALUES NEAR OR LESS THAN 0.10-INCH FOR A
MAJORITY OF THE REGION. FLOW ALOFT WILL TURN NELY WITH AN AMPLIFIED
FLOW OVER OF A POSITIVELY TILTED UPR RIDGE JUST OFFSHORE NOSING
TOWARD BC...AND AN UPR TROF EXTENDING FROM THE WESTERN GREAT LAKES
TO THE DESERT SW.


.HYDROLOGICAL CONDITIONS...

RIVERS IN NW CA AND SW OR CONTINUE TO RECEDE FOLLOWING THE HEAVY
RAINFALL THAT OCCURRED LAST WEEKEND.  ALL RIVERS IN THAT REGION HAVE
FALLEN BELOW MONITOR LEVELS EXCEPT FOR THE SPRAGUE RIVER AT BEATTY.
IT SHOULD FALL BELOW MONITOR IN THE NEXT FEW HOURS.

THE SACRAMENTO RIVER CONTINUES TO RECEDE AS WELL.  THE ONLY WEIR
LEFT FLOWING IS TISDALE.  IT SHOULD STOP FLOWING DURING THE EARLY
MORNING OF DECEMBER 24TH.

SMALL RISES CAN BE EXPECTED IN MANY NORTHERN CALIFORNIA RIVERS
DECEMBER 24-25TH.  HOWEVER, NO LOCATIONS ARE EXPECTED TO COME NEAR
MONITOR LEVELS.


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

DRK/KL/DRK/BW

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