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 SAT DEC 20 2014

...SYSTEM BRINGING PRECIP TO NORTHERN CA TODAY AND TOMORROW...
...BREAK EARLY IN THE WEEK WITH A POTENTIAL SYSTEM CHRISTMAS EVE AND
DAY...

.24 HOUR PRECIPITATION TOTALS (ENDING DEC 20 AT 400 AM PST)...

A SYSTEM MOVING THROUGH YESTERDAY BROUGHT PRECIP TO MUCH OF THE
REGION...WHILE A SECOND BEGAN MOVING IN EARLY THIS AM AS WELL. THE
SMITH BASIN PICKED UP HIGHEST 24-HR TOTALS...WITH AMOUNTS FROM 1-2"
AND UP TO 2.5" OVER FAVORED UPSLOPE TERRAIN. AMOUNTS DROPPED OFF
QUICKLY TO THE SOUTH...WITH THE EEL R BASIN ONLY MEASURING 0.25-0.5"
PRECIP. A STRONGER PULSE MOVING THROUGH THE RUSSIAN AND NAPA BASINS
DELIVERED 0.6-1.2" PRECIP...WITH UP TO 2.5" IN ISOLATED AREAS OF
MARIN COUNTY. THE SANTA CRUZ MTNS GENERALLY RECEIVED 0.5-1" WITH UP
TO 2" OVER HIGHEST TERRAIN. THE SANTA LUCIA`S MEASURED LESS THAN
0.2" PRECIP.

FURTHER INLAND...THE W SLOPES OF THE SRN OREGON CASCADES MEASURED
0.5-1" PRECIP...WITH 0.25-5" EAST OF THE CREST. THE SHASTA DRAINAGE
RECEIVED 0.75-1.5" PRECIP. DOWN INTO THE NORTHERN SIERRA...THE
FEATHER BASIN MEASURED 1-2" PRECIP THROUGH EARLY THIS AM...WITH THE
AMERICAN MEASURING CLOSER TO 0.6-1.2" PRECIP. THE CENTRAL SIERRA
RECEIVED 0.5-1"...HIGHEST ON THE NORTHERN END CLOSE TO HIGHWAY 50.
THE SACRAMENTO VALLEY MEASURED AMOUNTS AROUND 0.5"...WITH UP TO 1"
THROUGH THE I-80 CORRIDOR. THE NORTHERN SAN JOAQUIN VALLEY MEASURED
A FEW HUNDREDTHS...WITH NOTHING FURTHER SOUTH THAN THAT.


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

IR AND WATER VAPOR IMAGERY THIS MORNING SHOWS A BROAD AREA OF
MOISTURE STREAMING INTO THE REGION...WITH RADAR PICKING UP PRECIP
OVER MUCH OF NORTHERN CA FROM I-80 NORTHWARD. LIGHTER SHOWERS ARE
OCCURRING IN THE LEADING EDGE...WHICH EXTENDS FROM THE BAY AREA EAST
ACROSS THE I-80 CORRIDOR AND INTO THE NORTHERN SIERRA FROM THE
FEATHER BASIN S TO THE AMERICAN. FURTHER TO THE NORTH...A SECONDARY
PULSE IS MOVING THROUGH THE NORTH COAST AND THROUGH THE TRINITY MTNS
NE INTO THE SRN OREGON CASCADES. RAINFALL RATES ARE GENERALLY 0.1-
0.2" PER HOUR...WITH FREEZING LEVELS AROUND 6000-FT NEAR THE CA/OR
BORDER...AND UP TO AROUND 7000-FT OVER THE SIERRA.

THIS WARM FRONTAL PRECIP PATTERN IS EXPECTED TO CONTINUE TODAY...FED
BY A VERY BROAD AND MOIST PWAT PLUME HANGING OFFSHORE. PEAK VALUES
ALONG THE COAST ARE BEING MEASURED AROUND 1.4" BY THE BLENDED TPW
PRODUCT...PROVIDING THE FUEL FOR THE ONSHORE FLOW PATTERN THAT`S
DEVELOPED. EXPECT A SIMILAR PICTURE TO PERSIST MOST OF THE DAY
TODAY...WITH PRECIP IN GENERALLY THE SAME AREAS. THERE MAY BE A BIT
OF A SOUTHERN PROGRESSION DURING THE AFTERNOON HOURS...BUT DON`T
EXPECT MUCH PRECIP TO MAKE IT SOUTH OF THE SANTA CRUZ AND SANTA
LUCIA MTNS...OR DOWN PAST THE CENTRAL SIERRA.

OVERNIGHT TONIGHT...THE WAA PATTERN SHOULD SHIFT NORTHWARD...DRYING
AREAS AROUND THE I-80 CORRIDOR BUT KEEPING PRECIP GOING STRONG FROM
CAPE MENDOCINO NORTHWARD AND ALONG THE W SLOPES OF THE SRN OREGON
CASCADES. INCREASED PRECIP ALONG THE SMITH BASIN ESPECIALLY DURING
THE OVERNIGHT HOURS AND THROUGH SUNDAY. FINALLY EXPECT THE PATTERN
TO BREAK DOWN SUNDAY NIGHT AS RIDGING BUILDS IN FROM THE EASTERN
PACIFIC...BRINGING A BREAK TO PRECIP OVER THE ENTIRE REGION MONDAY
AND TUESDAY.

THE NEXT SHOT AT PRECIP COMES TO US ON WEDNESDAY...THOUGH MODELS ARE
ALL OVER THE PLACE WITH HOW THIS SYSTEM WILL AFFECT THE REGION. THE
12Z GFS BRINGS AN UPPER TROUGH THROUGH NORTHERN CA...WITH THE AXIS
SLIDING THROUGH THE NORTH COAST WED LATE MORNING AND AFTERNOON...
THEN INTO INTERIOR NORTHERN CA AND NEVADA WEDNESDAY NIGHT INTO
THURSDAY. THIS IS THE SHALLOWEST SOLUTION...AS THE 00Z EC DIGS THE
TROUGH DEEPER INTO CENTRAL CA...RESULTING IN PRECIP FURTHER SOUTH.
THE GEM IS THE MOST BULLISH...SWINGING THE TROUGH THROUGH THE
EASTERN PACIFIC AND FORMING A CUTOFF LOW OFF THE CA COAST...AND
BRINGING PRECIP THROUGH THE ENTIRE STATE WEDNESDAY NIGHT AND THURS.
THREW OUT THE GEM...AND WENT WITH A COMPROMISE BETWEEN THE GFS AND
EC FOR NOW. THE MODEL`S HAVE BEEN SWINGING WILDLY BACK AND FORTH FOR
THIS PERIOD...RESULTING IN A LOW CONFIDENCE EXTENDED FORECAST.


.HYDROLOGICAL CONDITIONS...

MINOR TO MODERATE RISES WERE OBSERVED ON MANY NORTHERN CALIFORNIA
COASTAL AND SAC VALLEY RIVERS AND STREAMS FROM PRECIP THAT FELL
WITHIN THE PAST 30 HOURS.  THERE WAS A PARTICULARLY NOTICEABLE
MODERATE RISE ON THE UPPER SACRAMENTO RIVER DUE TO CONTRIBUTIONS
FROM TRIBUTARIES BELOW SHASTA DAM.  PRECIPITATION FORECAST FOR TODAY
AND TOMORROW IS EXPECTED TO GENERATE MINOR RISES IN STAGE ON NORTH
COASTAL RIVERS AND STREAMS.  THE STAGE RISE WILL BE MOST NOTICEABLE
ON THE SMITH RIVER.

RENEWED OVERFLOW AT COLUSA WEIR BEGAN THIS MORNING AND IS EXPECTED
TO CONTINUE THROUGH MONDAY.

THERE IS A POSSIBILITY OF STAGES EXCEEDING MONITOR LEVEL AT COLUSA
BRIDGE THIS AFTERNOON.

OVERFLOW AT TISDALE WEIR IS EXPECTED TO CONTINUE THROUGH TUESDAY.

HIGH TIDE IS EXPECTED 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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