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 NOV 25 2014

...A FEW SHOWERS POSSIBLE NE NV TODAY OTHERWISE DRY THROUGH WED
NIGHT...
...MUCH WETTER PATTERN EXPECTED ACROSS THE AREA THU THROUGH THE
FIRST HALF OF NEXT WEEK...

.24 HOUR PRECIPITATION TOTALS (ENDING NOV 25 AT 400 AM PST)...

A WEAK WARM FRONT CAME THROUGH THE FAR NORTH OVERNIGHT...BRINGING UP
TO A TENTH OF AN INCH OF PRECIP TO AREAS ALONG THE CA/OR BORDER.
OTHERWISE...THE REGION REMAINED DRY.


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

THE PATTERN FEATURES A TROUGH ACROSS THE GREAT LAKES REGION AND A
RIDGE JUST OFF THE WEST COAST.  A WEAK SYSTEM MOVING ACROSS THE PAC
NW AND NW FLOW AT H7 AND ABOVE HAS BROUGHT LIGHT SHOWERS THIS
MORNING IN THE SRN OREGON CASCADES AND NEAR PORTIONS OF THE CA/OR
BORDER REGION AS WELL AS NE NV.  A STRAY SHOWER WILL BE POSSIBLE
INTO THE LATE MORNING/EARLY AFTERNOON PERIOD OVER NE NV AS THE AREA
OF PRECIP LIFTS NWD.

EXPECT THE RIDGE AXIS TO SHIFT INLAND OVER THE WRN STATES TONIGHT
INTO WED AHEAD OF AN APPROACHING TROUGH OVER THE ERN PAC.  A COLD
FRONT IS EXPECTED TO APPROACH THE NW CA COAST BY LATE WED NIGHT AND
THEN STALL NEAR FAR NW CA OR JUST OFF THE COAST THROUGH THU EVENING.
MODELS SHOW VARYING AMOUNTS OF PRECIP IN THIS REGION DURING THIS
PERIOD DEPENDING ON WHERE THE FRONT/MOISTURE PLUME STALLS BEFORE THE
FRONT LIFTS BACK TO THE NORTH A BIT THU NIGHT.

AS THE NEXT WAVE APPROACHES FROM THE WEST, THE MOISTURE PLUME IS
EXPECTED TO BEGIN TO PUSH SOUTH AND INLAND FRI/FRI NIGHT, SPREADING
MAINLY LIGHT AMOUNTS ACROSS MUCH OF NRN CA AND SRN OREGON, WITH MORE
MODERATE AMOUNTS POSSIBLE IN THE COASTAL BASINS.  BY LATE FRI NIGHT,
ENERGY ALOFT IS EXPECTED TO ENHANCE THE PRECIP ALONG THE MOISTURE
PLUME IN AN AREA ALREADY SEEING DECENT ONSHORE FLOW AND PW VALUES
NEAR 1", BRINGING ENHANCED TOTALS INTO THE MENDOCINO COUNTY AREA,
ALTHOUGH POSITIONING COULD BE SLIGHTLY FURTHER NORTH OR SOUTH
DEPENDING ON HOW THE DETAILS SHAPE UP.  AT THE SAME TIME, SLY 925 MB
WINDS ARE EXPECTED TO INCREASE TO 20-30 KTS IN THE NRN SACRAMENTO
VALLEY, HELPING TO ENHANCE TOTALS INTO THE SHASTA DRAINAGE.  PRECIP
SHOULD BE JUST STARTING TO INCREASE IN THE NRN SIERRA BY LATE FRI
NIGHT.

FREEZING LEVELS ARE EXPECTED TO START OFF ABOVE 10,000 FT AND LOWER
TO 7000-8000 FT ACROSS SRN OREGON AND FAR NRN CA AND 8000-10,000 FT
ACROSS THE NRN SIERRA AND NRN NV BY LATE FRI NIGHT.


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

BY SATURDAY MORNING...THE FRONTAL SYSTEM IS EXPECTED TO MOVE THROUGH
THE RUSSIAN/NAPA BASINS AND INLAND ACROSS THE NORTHERN SACRAMENTO
VALLEY. WHILE THE NORTHERN SIERRA MAY SEEM SOME PRECIP BY LATE
AFTERNOON AND EVENING...THE STRENGTHENING UPPER LOW WELL OFF THE
NORTH COAST AND DIGGING TROUGH WILL STEER THE UPPER JET INTO A MORE
SW-NE ORIENTATION AND HOLD PRECIP FURTHER TO THE WEST. THIS WILL
INSTEAD DRAG HEAVIER PRECIP DOWN THE COAST...INTO THE SANTA CRUZ
MTNS AND CENTRAL COAST OVERNIGHT.

SUNDAY MORNING SHOULD FINALLY BRING MORE CONSIDERABLE PRECIP INTO
THE NORTHERN SIERRA AS THE S/WV MOVES INLAND. MORE NOTABLE...
HOWEVER...IS THE FLOW PATTERN THAT DEVELOPS AHEAD OF THE NEXT WAVE
EXPECTED TO ARRIVE SUNDAY NIGHT. THOUGH TIMING IS STILL NOT HASHED
OUT BETWEEN THE GFS AND THE EC...BOTH MODELS INDICATE A PERIOD OF
INTENSE SOUTHERLY WINDS THROUGH THE SACRAMENTO VALLEY. THE 25/12Z
GFS PUTS 50+ KT SUSTAINED WINDS HOWLING THROUGH THE SAC VALLEY
SUNDAY MID-DAY...WHILE THE 25/00Z TAKES 40+ KT WINDS THROUGH THE
SAME AREA ABOUT 12-HRS LATER. EITHER WAY...WITH COPIOUS MOISTURE
AVAILABLE AND THIS STRONG FORCING...EXPECT A PERIOD OF VERY WINDY
CONDITIONS THROUGH THE REGION SUNDAY AFTERNOON OR NIGHT...AND PRECIP
OVER THE SHASTA DAM RESPONDING ACCORDINGLY.

THE UPPER LOW IS EXPECTED TO MAKE ITS EASTERLY MARCH SUNDAY NIGHT...
AND WHILE THE EC IS STILL MUCH SLOWER THAN THE GFS...LATEST RUNS OF
THE GFS SEEM TO BE TRENDING IN THAT DIRECTION. THE CANADIAN IS
SOMEWHERE IN BETWEEN FOR NOW. THE CURRENT FORECAST LEANS MORE
HEAVILY ON THE SLOWER EC...AND EXPECT A 6-12 HR PERIOD OF HEAVY
PRECIP TO MOVE THROUGH THE NORTH COAST AS EARLY AS SUNDAY NIGHT...BUT
MORE LIKELY MONDAY MORNING. THE REGION IS PLACED IN A VERY FAVORABLE
DYNAMIC ENVIRONMENT ON MONDAY...AND WIDESPREAD MODERATE TO HEAVY
PRECIP IS EXPECTED...ESPECIALLY OVER OROGRAPHICALLY FAVORED
LOCATIONS. AGAIN...THE EC IS SLOWER...BUT THE OVERALL PATTERN AND
DISTRIBUTION OF HEAVY PRECIP IS SIMILAR...WITH THE SHASTA BASIN
GETTING HIT HARD WITH THE POTENTIAL FOR 5"+ PRECIP AMOUNTS...AND 2-
5" PRECIP AMOUNTS OVER THE NORTHERN SIERRA. FREEZING LEVELS SHOULD
FALL TO AROUND 6000-FT OR LOWER ON MONDAY...ALLOWING MUCH OF WHAT
FALLS TO ACCUMULATE IN THE CURRENTLY MEAGER SNOWPACK.

ALSO BECAUSE OF THE TIMING DIFFERENCES...SOUTHERN CA IS UP IN THE
AIR AS TO WHEN TO EXPECT PRECIP TO BEGIN. MODELS DO HINT AT A
FAVORABLY MOIST SOUTH TO SOUTHWEST FLOW PATTERN DEVELOPING OVER THE
SBA SOUTH COAST AND VENTURA COUNTY MOUNTAINS...WHICH HAS THE
POTENTIAL TO PRODUCE HEAVY PRECIP OVER THOSE AREAS AS WELL. FOR
NOW...BELIEVE THAT IS JUST OUTSIDE OF THE FORECAST WINDOW...AS
SUGGESTED BY THE EC.

HOPEFULLY THE MODELS COME INTO LINE OVER THE NEXT FEW DAYS...AS THE
END OF THE WEEKEND AND START OF THE WORK WEEK LOOK TO BE THE WETTEST
AND SNOWIEST OF THE YEAR SO FAR.


.HYDROLOGICAL CONDITIONS...

THE RIVERS WILL REMAIN NEAR CURRENT LEVELS FOR THE NEXT 3-4 DAYS.
THE PRECIPITATION OVER THE WEEKEND WILL RESULT IN MODEST RISES ALONG
THE NORTHERN COAST OF CALIFORNIA AND THE UPPER SACRAMENTO RIVER
SYSTEM.  NO RIVERS ARE EXPECTED TO RISE ABOVE MONITOR LEVELS DUE TO
THE WEEKEND STORM; HOWEVER, THIS MAY CHANGE AS WE GET CLOSER TO THE
WEEKEND.


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

JM/KL/JM/BW

$$



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