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 SUN DEC 21 2014

...PRECIP DECREASING OVER THE NORTH COAST THROUGH THE DAY...
...DRY TO START THE WEEK WITH A POSSIBLE SYSTEM MOVING THROUGH THE
NORTH CHRISTMAS EVE AND DAY...

.24 HOUR PRECIPITATION TOTALS (ENDING DEC 21 AT 400 AM PST)...

A SYSTEM MOVING THROUGH BROUGHT PRECIP TO THE NORTHERN TIER OF CA
AND MUCH OF NV. THIS PATTERN BROUGHT MODERATE TO LOCALLY HEAVY
PRECIP TO THE NORTH COAST AND W SLOPES OF THE SRN OREGON CASCADES.
OVER THE LATTER...3-4.5" HAS FALLEN AS OF 4 AM...WITH UP TO AN INCH
EAST OF THE CREST. OVER THE SMITH...AMOUNTS RANGE FROM 4-6". PRECIP
QUICKLY FALLS OFF TO THE SOUTH...DOWN TO AROUND 1-1.5" AROUND CAPE
MENDOCINO...0.5-1" OVER THE EEL R BASIN...AND 0.25-0.5 OVER THE
RUSSIAN. AROUND 0.05-0.15" FELL FROM THE SF BAY SOUTH TO THE SANTA
LUCIA RANGE AND DRY TO THE SOUTH.

OVER SHASTA...0.75-1.25" PRECIP FELL...WITH SIMILAR AMOUNTS MEASURED
OVER THE FEATHER AND AMERICAN BASINS. THE CENTRAL SIERRA RECEIVED
AROUND 0.4-0.8" PRECIP...WITH LESS THAN A TENTH MEASURED OVER THE
SOUTHERN SIERRA AS WELL AS EAST OF THE CREST. OVER THE SACRAMENTO
VALLEY...AMOUNTS WERE GENERALLY LIGHT AND LESS THAN A QUARTER OF AN
INCH OVER THE NORTHERN HALF AND LESS THAN A TENTH ALONG THE SOUTHERN
SIDE.

OVER NEVADA...PRECIP WAS HEAVIEST OVER THE RUBY MTNS...WITH 0.75-
1.25" MEASURED THROUGH THE EARLY MORNING HOURS...WITH 0.1-0.3"
PICKED UP ELSEWHERE. THE SOUTHERN THIRD REMAINED DRY.


.METEOROLOGICAL CONDITIONS (SUN AM - SAT AM)...

ACTIVE MORNING ALONG THE NORTH COAST TODAY...WHERE A MOIST WARM AIR
ADVECTIVE PATTERN HAS REMAINED STATIONARY OVER THE SMITH BASIN FOR
NEARLY THE LAST 24-HRS. THIS HAS BROUGHT CONSISTENT RAINFALL RATES
OF 0.2" PER HOUR FOR ALMOST THAT ENTIRE TIME PERIOD...BUT VERY
LOCALIZED TO THAT BASIN AND NORTHWARD. MODERATE ONSHORE FLOW WITH
LOW LEVEL WINDS 10-25 KTS HAVE DRIVEN THE BROAD MOISTURE PLUME INTO
THE COASTAL RANGES...ALLOWING FOR A PERIOD OF PROLONGED AND
EFFICIENT UPSLOPE PRECIP. LATEST AMSU PASS AROUND 11Z SHOWED 1.25-
1.4" PWAT AMOUNTS MOVING ONSHORE...WHICH EXPLAINS THE HIGH PRECIP
TOTALS SO FAR DESPITE A MEAGER LOOKING RADAR PICTURE.

WHILE ONSHORE FLOW IS EXPECTED TO CONTINUE THROUGH THE DAY TODAY...
IR IMAGERY SHOWS SOME WARMING CLOUD TOPS BEHIND THE AREA MOVING
THROUGH NOW...SIGNALING A SLOW ENDING TO THE HIGHER PRECIP RATES.
BEST MOISTURE IS ALSO EXPECTED TO CUT OFF AS THE DAY PROGRESSES...
FURTHER ENDING THE PROLONGED PERIOD OF HEAVY PRECIP. WHILE PRECIP IS
EXPECTED TO CONTINUE THROUGH THE DAY AND OVERNIGHT TONIGHT OVER THE
SMITH BASIN...UPPER KLAMATH...AND W SLOPES OF THE SRN OREGON
CASCADES...RATES WILL RAPIDLY DECREASE UNTIL THE SYSTEM MOVES OFF TO
THE EAST EARLY MONDAY.

MONDAY AND TUESDAY ARE EXPECTED TO REMAIN DRY OVER THE REGION WITH
HIGH PRESSURE BUILDING IN FROM THE PACIFIC. DO EXPECT FOG-PRONE
AREAS TO GET HIT HARD DURING THIS TIME...WITH THE COMBINATION OF
HIGH PRESSURE...MOSTLY CLEAR SKIES OVERNIGHT...AND COPIOUS GROUND
MOISTURE FROM THE RECENT RAINS.

MODELS CONTINUE TO SWING BACK AND FORTH REGARDING THE SLIDER MOVING
THROUGH NORTHERN CA ON CHRISTMAS EVE AND DAY. MAINLY USED THE 00Z
GFS AND EC GUIDANCE TO COME UP WITH A PLAN FOR THIS TIME PERIOD...AS
THE 06Z GFS WAS PRETTY OUT OF LINE WITH THE LATEST EC. MODELS
INDICATE AN UPPER TROUGH SWINGING SHALLOWLY THROUGH THE NORTHERN
PIECE OF CA...THEN DEEPENING SOME AS IT MOVES THROUGH NRN NEVADA.
THE EC IS THE QUICKER OF THE TWO...WITH PRECIP BEGINNING WEDNESDAY
AFTERNOON...WHILE THE GFS HOLDS OFF UNTIL THE EVENING. THE EC ALSO
MOVES IT THROUGH MORE QUICKLY...BY LATE THURS MORNING COMPARED TO
THE GFS`S THURS LATE AFTERNOON. THE GEM SOL`N IS A MAJOR OUTLIER
(THOUGH HAS RUN TO RUN CONSISTENCY)...DEVELOPING A CUTOFF LOW FROM
THE TROUGH AND DRAGGING IT DOWN THE WEST COAST. THREW THAT ONE OUT
OF THE MIX FOR NOW. CONFIDENCE GENERALLY REMAINS LOW FOR THIS PERIOD.

BY FRIDAY...EASTERN PACIFIC RIDGING REBUILDS AND BRINGS DRY
CONDITIONS TO THE REGION FOR THE REMAINDER OF THE PERIOD.


.HYDROLOGICAL CONDITIONS...

THE HEAVY PRECIPITATION THAT FELL YESTERDAY AND THIS MORNING
COMBINED WITH ALREADY SATURATED SOIL CONDITIONS IS PRODUCING A
MODERATE RISE ON THE SMITH AND MAD RIVERS.  THE SMITH RIVER AT DR
FINE BRIDGE AND THE MAD RIVER AT ARCATA ARE CURRENTLY ABOVE MONITOR
STAGE.  BOTH ARE EXPECTED TO CREST AND BEGIN RECEDING TODAY.

OVERFLOW AT COLUSA WEIR IS EXPECTED TO CONTINUE THROUGH MONDAY.

STAGES ON THE SACRAMENTO RIVER AT COLUSA BRIDGE WERE BRIEFLY ABOVE
MONITOR LEVEL FROM YESTERDAY EVENING THROUGH THIS MORNING.

OVERFLOW AT TISDALE WEIR IS EXPECTED TO CONTINUE THROUGH LATE
WEDNESDAY MORNING.

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

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


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

JM/AT

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