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HYDROMETEOROLOGICAL DISCUSSION
NATIONAL WEATHER SERVICE / CALIFORNIA NEVADA RFC / SACRAMENTO CA
930 AM PST THU DEC 18 2014

...NEXT SYSTEM ARRIVES TONIGHT INTO TOMORROW...
...WARM FRONT TO BRING PRECIP TO AREAS NORTH OF I-80 ON SAT...

.24 HOUR PRECIPITATION TOTALS (ENDING DEC 18 AT 400 AM PST)...

AN EXITING SYSTEM BROUGHT PRECIP TO SOUTHERN CA YESTERDAY MORNING
INTO THE EARLY AFTERNOON HOURS...WHILE A SECOND ONE MOVING INTO THE
AREA BROUGHT PRECIP TO THE NORTHERN 2/3 OF CA STARTING IN THE
AFTERNOON HOURS. OVER THE SMITH BASIN...0.75-1.25" PRECIP WAS
REPORTED...WITH UP TO 1.6" MEASURED IN HIGHER FAVORED TERRAIN. FROM
CAPE MENDOCINO SOUTH THROUGH THE RUSSIAN R BASIN...AMOUNTS RANGED
FROM 0.3-0.6" AMOUNTS WITH A COUPLE FAVORED LOCATIONS PICKING UP
0.8". OVER THE SANTA CRUZ MTNS...0.25-0.5" PRECIP WAS MEASURED....
WITH 0.1-0.25" OVER THE SANTA LUCIA RANGE.

FURTHER INLAND...THE W SLOPES OF THE SRN OREGON CASCADES MEASURED UP
TO A THIRD OF AN INCH...WITH LESS THAN 0.1" EAST OF THE CREST. OVER
THE SHASTA DRAINAGE...PRECIP RANGED FROM 0.75"-1.25"...WITH UP TO
1.75" OVER THE EASTERN HALF OF THE DRAINAGE. THE FEATHER BASIN
MEASURED AROUND 0.75-1" PRECIP...WHILE THE AMERICAN PICKED UP 0.5-
0.75". THE CENTRAL SIERRA MEASURED AROUND A THIRD OF AN INCH...WITH
SLIGHTLY LESS OVER THE SOUTHERN SIERRA AROUND 0.1-0.25". THE
SACRAMENTO VALLEY MEASURED AROUND 0.05-0.15"...WITH LESS THAN 0.1"
OVER THE SAN JOAQUIN VALLEY.

SOUTHERN CA SAT AMOUNTS FROM 0.1" OR LESS OVER COASTAL LOS ANGELES
COUNTY...INCREASING TO 0.4-0.7" OVER THE SAN GABRIEL MTNS. COASTAL
AREAS FROM ORANGE CO SOUTH MEASURED 0.2-0.4"...WHILE INLAND FOOTHILL
AND MTN LOCATIONS RECEIVED 0.5-0.7" PRECIP. DESERTS MEASURED A FEW
HUNDREDTHS.


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

ANOTHER S/WV TROF IS EXITING THE REGION TO THE EAST...WHILE THE NEXT
CROSSING 140W JUST TO THE NORTH OF 40N THIS MORNING. A FEW SHOWERS
REMAIN THIS MORNING NEAR PT CONCEPTION...THE HIGHER TERRAIN OF
NORTHERN CA...AND EASTERN NEV.

A QUICK MOVING UPR RIDGE WILL CROSS THE REGION TODAY. AFTER
SUNSET...THE NEXT S/WV TROF WILL MOVE TOWARD THE PACNW WITH THE COLD
FRONT NEARING THE NORTH COAST. PRECIP WILL BE ON THE INCREASE DURING
THE EVENING PERIOD AS THE NARROW MOISTURE PLUME CONVERGING AHEAD OF
THE BOUNDARY INTERSECTS THE COAST. PW VALUES PEAK OFFSHORE JUST OVER
THE 1.00-INCH MARK. THE 18/00Z EC IS A TAD BIT FASTER THAN THE
18/00Z GFS...18/12Z NAM...AND 18/09Z SREF. FOLLOWED CLOSER TO THE
SLIGHTLY SLOWER PROGRESSION OF THE PRECIP. WITH THE S/WV TROF MOVING
INLAND ACROSS THE PACNW AND A WEAKER DISTURBANCE MOVING ACROSS THE I-
80 CORRIDOR...THE HEAVIEST PRECIP AMOUNTS WILL FALL NORTH OF A SF
BAY AREA TO LAKE TAHOE LINE. BY FRIDAY EVENING...THE COLD FRONT
WASHES OUT ACROSS CENTRAL CA WITH LIGHT PRECIP.

INTO SATURDAY...AN UPR RIDGE BEGINS TO BUILD TO THE SW OF THE REGION
WITH THE NEXT MOISTURE PLUME DIRECTED TOWARD THE OREGON COAST.
PRECIP NEAR THE CA/ORE BORDER WILL BE THE RESULT OF A WARM FRONT
MOVING ACROSS THE REGION. MOIST ONSHORE FLOW WILL GENERATE THE BEST
AMOUNTS OVER THE SOUTHERN OREGON CASCADES AND THE COASTAL MOUNTAINS
FROM CAPE MENDOCINO NORTH TO THE SMITH RIVER BASIN.


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

MODELS START OUT QUITE DIFFERENT ON SUNDAY MORNING...WITH THE 00Z
AND 06Z GFS SOL`NS QUICKLY WRAPPING UP LIGHT PRECIP OVER NRN CA BY
AFTERNOON...AND THE 00Z EC MOVING MODERATE PRECIP THROUGH THE SMITH
BASIN FOR SUN MORNING AND AFTERNOON...FINALLY LIGHTENING AND
CLEARING MONDAY MORNING. PART OF THE DRIVER FOR THESE DIFFERENCES
LIES IN HOW QUICKLY THE EXTENDED MODELS BUILD HIGH PRESSURE BACK
INTO THE EASTERN PACIFIC ON MONDAY. THE GFS...AS YOU`D
EXPECT...DEVELOPS THE RIDGE STRONGER AND FASTER...WHICH KICKS PRECIP
OUT SOONER THAN THE EC. KEEPING WITH THE EC SOL`N FOR NOW...THOUGH
NOT BUYING FULLY INTO THE HIGH PRECIP TOTALS.

THIS RIDGE WILL KEEP CONDITIONS HIGH AND DRY THROUGH AT LEAST
WEDNESDAY MORNING...WITH TEMPS A BIT ABOVE SEASONAL AVERAGES. ON
CHRISTMAS EVE...MODELS ARE BEGINNING TO HONE IN ON THE DETAILS OF A
SYSTEM TO BRING PRECIP WEDNESDAY NIGHT INTO CHRISTMAS DAY TO
NORTHERN CA AND NV. WHILE BOTH THE GFS AND EC PRESENT AN INSIDE
SLIDER-TYPE SYSTEM...THE DETAILS ARE STILL UNCLEAR. THE CURRENT 06Z
GFS IS THE SHALLOWEST...WITH JUST A WEAK PULSE OF ENERGY SLIDING
THROUGH THE SMITH AND UPPER KLAMATH WEDNESDAY LATE AM THROUGH
AFTERNOON...THEN PUSHING INTO NORTHERN NEVADA OVERNIGHT AND INTO
THURS AM. THE 00Z DIGS THE TROUGH MUCH MORE...PRESENTING A MODERATE
RAIN/SNOW EVENT FOR NORTHERN CA AND NV AND THE SIERRA WEDNESDAY
AFTERNOON THROUGH THURSDAY MORNING. WILL KEEP AN EYE ON THIS SYSTEM
AS IT MOVES CLOSER INTO THE FORECAST WINDOW.


.HYDROLOGICAL CONDITIONS...

RENEWED RISES ARE EXPECTED INTO THE WEEKEND ACROSS MOST OF THE
NORTHERN HALF OF CALIFORNIA.  THE SOUTHERN HALF OF CALIFORNIA CAN
EXPECT SLOWLY RECEDING RIVER CONDITIONS AS DRIER WEATHER PREVAILS.
ON THE SACRAMENTO RIVER OVERFLOW INTO THE SUTTER BYPASS IS OCCURRING
AT COLUSA AND TISDALE WEIRS THIS MORNING AND THE HIGH TIDE AT RIO
VISTA BRIDGE IN THE DELTA IS EXPECTED TO RISE ABOVE MONITOR LEVEL
FOR THE NEXT FEW DAYS.  ALL OTHER RIVER LEVELS ARE EXPECTED TO
REMAIN BELOW MONITOR LEVELS THROUGH THE WEEKEND.

RESERVOIR STORAGE CONTINUES TO INCREASE AT MOST NORTHERN CALIFORNIA
RESERVOIRS WHILE THE LARGER RESERVOIRS ON THE SAN JOAQUIN AND TULARE
LAKE RIVER SYSTEMS CONTINUE WITH VERY LITTLE INFLOW IMPROVEMENT.


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

JM/DRK/JM/AM

$$




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