Hydrometeorological Discussion
Issued by NWS California-Nevada RFC

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AGUS76 KRSA 221734
HMDRSA

HYDROMETEOROLOGICAL DISCUSSION
NATIONAL WEATHER SERVICE / CALIFORNIA NEVADA RFC / SACRAMENTO CA
930 AM PST MON DEC 22 2014

...INCREASING CONFIDENCE IN PRECIP OVER NORTHERN CA BEGINNING
WEDNESDAY...
...PRECIP POSSIBLE AGAIN FOR FAR NORTHERN AREAS THIS WEEKEND...


.24 HOUR PRECIPITATION TOTALS (ENDING DEC 22 AT 400 AM PST)...

A MOIST ONSHORE FLOW ACROSS THE NRN PORTION OF THE REGION ALONG WITH
AN UPPER JET AND STATIONARY FRONT JUST TO THE NORTH BROUGHT
PRECIPITATION TO MUCH OF NRN CA/SRN OREGON/NRN NV DURING THE PERIOD.
A WEAK DISTURBANCE ALOFT ALSO GENERATED A FEW SHOWERS OVER SRN CA.
STARTING ON THE NORTH COAST, 24-HOUR TOTALS WERE GENERALLY 2-3.4" IN
THE SMITH BASIN AND 0.1-0.6" IN THE LOWER KLAMATH, LOCALLY WETTER
NEAR THE COAST.  TOTALS WERE GENERALLY 0.2" OR LESS OVER THE
REMAINDER OF THE NORTH COAST AND FURTHER SOUTH ALL THE WAY TO THE
SANTA CRUZ MTNS.  A FEW SACRAMENTO VALLEY SITES PICKED UP 0.01-
0.02", WITH UP TO 0.1" IN THE LAKE SHASTA AREA LOCATIONS IN THE
UPPER KLAMATH PICKED UP ANYWHERE FROM A FEW HUNDREDTHS OF AN INCH
TO 0.5" IN THE LOWER ELEVATIONS, WITH GENERALLY 3.2-4.6" IN THE
HIGHER ELEVATIONS.  NE CA SAW AMOUNTS UP TO 0.2", WHILE THE NRN/
CNTRL SIERRA PICKED UP 0.25" OR LESS, WETTEST NORTH OF US-50, WITH A
FEW HUNDREDTHS OF AN INCH ON THE EAST SIDE OF THE CREST.  INTO NRN
NV, AMOUNTS WERE GENERALLY 0.1-0.8" IN THE LOWER ELEVATIONS AND 0.7-
1.7" IN THE HIGHER ELEVATIONS.  AN EXCEPTION WAS LOCATIONS CLOSER TO
CNTRL NV, WHERE ONLY A FEW HUNDREDTHS OF AN INCH WERE NOTED.
FINALLY, A FEW STATIONS IN SANTA BARBARA AND SAN DIEGO COUNTIES
NOTED VERY LIGHT AMOUNTS GENERALLY ONLY 0.01".



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

WATER VAPOR IMAGERY THIS MORNING SHOWS THE EASTERN PACIFIC RIDGE
BUILDING...WITH ITS AXIS CENTERED AROUND 135W CURRENTLY. RIDGING IS
BEGINNING TO BUILD INTO THE WEST COAST...WITH DENSE FOG BLANKETING
MUCH OF THE INTERIOR VALLEYS THANKS TO THE COPIOUS AVAILABLE
MOISTURE FROM RECENT RAINS. OTHERWISE...LIGHT PRECIP LEFTOVER FROM A
WAA PATTERN IS WRAPPING UP OVER THE SMITH AND UPPER KLAMATH
BASINS...AND THE W SLOPES OF THE SOUTHERN OREGON CASCADES. THERE IS
ALSO AN AREA OF PRECIP MOVING THROUGH NORTHEASTERN NEVADA...BUT
SHOWERS THERE TOO SHOULD COME TO A CLOSE BY THE EVENING HOURS.

WHILE RIDGING AND DRY CONDITIONS WILL DOMINATE THROUGH TUESDAY...THE
BIGGER CONCERN IS OF A SYSTEM MORE CLEARLY TAKING AIM AT NORTHERN CA
WEDNESDAY AND THURSDAY. WHILE MODELS HAVE DANCED AROUND THE DETAILS
FOR THIS TIME PERIOD...FINALLY SOME SENSE OF AGREEMENT IS SHAKING
OUT. AN UPPER TROUGH IS EXPECTED TO DROP SOUTH OUT OF THE PACIFIC
NORTHWEST...BRINGING A FRONTAL SYSTEM TO THE NORTH COAST BY LATE WED
MORNING/EARLY AFTERNOON. THIS SHOULD QUICKLY SWING THROUGH THE
REMAINDER OF NRN CA DURING THE AFTERNOON AND EVENING HOURS...
BRINGING A PERIOD OF HEAVY SHOWERS TO THE NORTHERN SIERRA MOST
LIKELY WED EVENING...THEN QUICKLY MOVING INTO NEVADA OVERNIGHT INTO
THURS AM. THE 12Z GFS BRINGS THE SYSTEM KNOCKING ON OUR DOOR THE
QUICKEST...WITH MODERATE PRECIP BEGINNING OVER THE SMITH BASIN BY
LATE WED AM. THE 12Z NAM...00Z EC...AND 00Z CANADIAN ARE A BIT
SLOWER...HOLDING OFF UNTIL THE AFTERNOON HOURS. TIMING IN THE
MORNING QPF FORECAST REFLECTS THE GREATER MODEL CONSENSUS OVER THE
FASTER GFS. ALSO DECLINED TO GO WITH PRECIP OVER SRN CA AS THE EC
HINTED AT WITH ITS DEEPER TRAJECTORY LATE WED PM...AND STUCK WITH A
LITTLE MORE SHALLOW TROUGH BRINGING LIGHT PRECIP THROUGH THE CENTRAL
AND SOUTHERN SIERRA BUT NO FURTHER.


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

THE PERIOD STARTS OFF WITH AN UPPER TROUGH SHIFTING EAST FROM NV
INTO UT, AND AN ASSOCIATED COLD FRONT DIVING SE ACROSS THE REGION.
BY THIS POINT, MOST SHOWER ACTIVITY SHOULD BE CONFINED TO NERN
PORTIONS OF NV NEAR THE TROUGH AND AIDED BY STRONG NWLY UPSLOPE FLOW
AT H7, ALTHOUGH AVAILABLE MOISTURE WILL BE DROPPING BY THU MORNING.
ADDITIONAL SHOWERS ARE EXPECTED IN THE SRN OREGON CASCADES NEAR AN
UPPER JET.  EXPECT SHOWERS TO WIND DOWN DURING THE DAY THU.  THE
NEXT TROUGH IS EXPECTED TO DROP INTO THE PAC NW BY SAT, BRINGING
ANOTHER CHANCE OF PRECIP TO THE FAR NORTH, ALTHOUGH THE LATEST ECMWF
IS MUCH MORE SLY WITH THE TROUGH AND SHOWS PRECIP REACHING MUCH OF
NRN CA/NV BY SAT NIGHT.  EXPECT FREEZING LEVELS 3000-4000 FT THU AND
3500-5000 FT SAT INTO SAT NIGHT.


.HYDROLOGICAL CONDITIONS...

RUNOFF FROM PRECIPITATION THAT FELL DURING THE PAST 30 HOURS
AFFECTED THE MAD RIVER AT ARCATA AND ESPECIALLY THE SMITH RIVER AT
DR FINE BRIDGE...BOTH CRESTING JUST ABOVE MONITOR STAGE.  BOTH THE
SMITH AND MAD RIVERS HAVE SINCE RECEDED BELOW MONITOR LEVELS.

OVERFLOW AT COLUSA WEIR IS FORECAST TO END TOMORROW MORNING.

OVERFLOW AT TISDALE WEIR IS EXPECTED TO END WEDNESDAY.

EXPECT HIGH TIDE AT RIO VISTA BRIDGE TO EXCEED MONITOR STAGE DURING
THE NEXT 3 DAYS.

ALL OTHER RIVER FORECAST POINTS ARE EXPECTED TO REMAIN BELOW MONITOR
LEVELS FOR THE NEXT FEW DAYS.


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

KL/JM/KL/AT

$$



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