Hydrometeorological Discussion
Issued by NWS California-Nevada RFC

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AGUS76 KRSA 261729
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HYDROMETEOROLOGICAL DISCUSSION
NATIONAL WEATHER SERVICE / CALIFORNIA NEVADA RFC / SACRAMENTO CA
930 AM PST WED NOV 26 2014

...DRY TODAY THEN WET PATTERN BEGINS THU LASTING FOR SEVERAL DAYS...

.24 HOUR PRECIPITATION TOTALS (ENDING NOV 26 AT 400 AM PST)...

RIDGING OVER THE AREA KEPT THE REGION DRY OVER THE LAST 24-HRS.


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

TODAY IS EXPECTED TO BE THE LAST DRY DAY ACROSS THE REGION FOR THE
NEXT SEVERAL DAYS AS A RIDGE AXIS SHIFTS EAST ACROSS THE WRN STATES.
BY EARLY THU, EXPECT THE RIDGE AXIS TO BE PUSHING INTO THE GREAT
BASIN, WITH A TROUGH WEST OF 140W.  A SLOW-MOVING COLD FRONT IS
EXPECTED TO MOVE INTO THE PAC NW AND FAR NW CA, STRETCHING OFF TO
THE SW, AND REMAIN NEARLY STATIONARY THU MORNING THROUGH THU NIGHT.
EXPECT LIGHT TO MODERATE PRECIP ACROSS FAR NW CA INTO SRN OREGON
THROUGH THIS PERIOD, HEAVIEST IN THE SMITH BASIN AND NEAR THE
CASCADE CREST.  AS THE TROUGH EDGES EWD TOWARD THE WEST COAST, THE
FRONT IS EXPECTED TO FINALLY MAKE MORE SIGNIFICANT FORWARD PROGRESS
AND SPREAD PRECIP ACROSS MUCH OF NRN CA/SRN OREGON DURING THE DAY
FRI AND FRI NIGHT.  WITH A MODERATE ONSHORE FLOW AND LACK OF STRONG
DYNAMICS ALOFT EARLY ON, AMOUNTS ARE EXPECTED TO BE MAINLY LIGHT
WITH PERHAPS SOME MORE MODERATE AMOUNTS NEAR THE COAST THROUGH THE
EVENING.  LATER FRI NIGHT, A WEAK VORT MAX ALOFT COULD HELP TO
ENHANCE TOTALS, ESPECIALLY ALONG THE MOISTURE PLUME AIMED ROUGHLY AT
THE RUSSIAN BASIN ACROSS TO THE FAR NRN SIERRA.  FREEZING LEVELS ARE
EXPECTED TO START OFF ABOVE 10,000 FT AND LOWER TO 7000-7500 FT
ACROSS SRN OREGON AND FAR NRN CA AND 7500-9000 FT ACROSS THE NRN
SIERRA BY LATE FRI NIGHT.


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

COMPLICATED FORECAST FOR THE LATTER HALF OF THE PERIOD TODAY...AS
MODELS CONTINUE TO CHANGE THEIR EXPECTED TIMING OF THE LAST STORM IN
THE FORECAST. SATURDAY AND SUNDAY ARE IN FAIRLY DECENT ALIGNMENT AT
LEAST...BEFORE THE GREAT MODEL DIVIDE.

THE TAIL END OF THE FIRST WAVE SHOULD KEEP PUSHING THROUGH SATURDAY
MORNING AND AFTERNOON...WITH HEAVIER BANDS FOCUSED ACROSS THE SF BAY
AND SANTA CRUZ MOUNTAINS...AS WELL AS OVER THE NORTH COAST. PRECIP
WILL CONTINUE MUCH OF THE DAY OVER THOSE AREAS AS THE SYSTEM VERY
SLOWLY SAGS...BUT CONTINUES TO ENTRAIN MORE OF THE 1" MOISTURE PLUME
AIMED AT THE SF BAY INLAND. THE S/WV PICKS UP AND FINALLY PUSHES
THROUGH THE STATE SUNDAY MORNING...WHICH BRINGS A SHARP INCREASE IN
SOUTHERLY WIND FLOW UP THE SACRAMENTO VALLEY. THIS SHOULD BRING A
BUMP IN PRECIP TO AREAS BELOW SHASTA DAM AS WELL AS MUCH OF THE
COAST FROM CAPE MENDOCINO SOUTH TO THE MONTEREY BAY. EXPECTED
MODERATE PRECIP TO CONTINUE OVER THE FEATHER THROUGH THE LATE
MORNING HOURS BEFORE THE REGION TAKES A QUICK SHOWERY BREAK BEFORE
THE BIGGER SYSTEM MOVES IN.

ONCE SUNDAY EVENING ROLLS AROUND...ALL BETS WITH MODEL AGREEMENT ARE
OFF. AT FORECAST TIME...THE LATEST GFS VERSION AVAILABLE WAS THE
26/06Z RUN...WHICH IS QUITE DISSIMILAR FROM THE 12Z RUN THAT HAS
SINCE ARRIVED. BASED ON MODELS AVAILABLE AT THE TIME...FELT THE 06Z
GFS WAS A PRETTY GOOD COMPROMISE BETWEEN THE NOW *MUCH* SLOWER EC
AND THE FASTER 26/00Z GFS. THE 00Z EC IS A SOLID 36-HOURS SLOWER
WITH BRINGING IN THIS VIGOROUS UPPER LOW THAN THE GFS HAS
BEEN...HOLDING OFF ON ANY CONSIDERABLE PRECIP UNTIL TUESDAY AM. THE
GFS GENERALLY BRINGS HEAVIER PRECIP IN LATE SUNDAY NIGHT...THOUGH
SOME ENSEMBLE MEMBERS ARE HINTING AT A SLOWER PROGRESSION. FUNNY...
CONSIDERING THE EC ENSEMBLE MEAN ERRS A BIT FASTER THAN THE
OPERATIONAL RUN. AGAIN...FELT THE 06Z GFS WAS THE BEST TO GO BY FOR
NOW IN TERMS OF TIMING. *BUT*...AT THE TIME OF WRITING THIS...THE
12Z RUN HAS COME IN...AND IS ABOUT 12-HRS SLOWER THAN THE 06Z GFS.
STILL NOT QUITE AS SLUGGISH AS THE EC...BUT COULD BE HINTING AT
CHANGES IN THAT DIRECTION.

SO WITH THE FORECAST CENTERED ON THE 06Z GFS...EXPECT HEAVY PRECIP
TO AGAIN MOVE INTO THE REGION MONDAY MORNING...WITH ANOTHER ROUND OF
INTENSE SOUTH TO SOUTHWEST WINDS  OVER THE RUSSIAN/NAPA
BASINS AND THROUGH THE SACRAMENTO VALLEY. GOOD FRONTOGENESIS
DEVELOPS IN A LINE THROUGH THOSE AREAS MON AM...AND THE STRONG
DYNAMICS AND AMPLE MOISTURE WILL MAKE FOR A WET COMBO. THE GFS EVEN
HINTS AT SOME NEAR-2" 6-HR TOTALS OVER THE RUSSIAN AND SHASTA BASINS
DURING THIS TIME. THE LOCALLY HEAVY PRECIP SHOULD CONTINUE THROUGH
THE AFTERNOON HOURS...GRADUALLY SLIDING SOUTH INTO THE NORTHERN AND
CENTRAL SIERRA AS WELL AS THE CENTRAL COAST.

IF THIS ITERATION OF THE GFS VERIFIES...EXPECT THE UPPER LOW TO
CONTINUE TO MOVE TOWARDS THE SF BAY THROUGH THE EVENING ON MONDAY
AND INTO THE OVERNIGHT HOURS TUESDAY. SOUTHERN CA SHOULD GET HIT
WITH MODERATE SOUTH TO SOUTHWEST WINDS EARLY TUESDAY MORNING...
WHILE A MORE WESTERLY DIRECTION OVER SAN DIEGO COUNTY WILL AID IN
HIGHER PRECIP TOTALS THERE AS WELL. THE LOW SHOULD CONTINUE TO TRACK
DOWN THE COAST THROUGH THE DAY ON TUESDAY.

AGAIN...I CANNOT STRESS ENOUGH THE UNCERTAINTY IN TIMING OF THE LONG
TERM FORECAST. WHILE GENERAL AMOUNTS HAVE NOT VARIED MUCH...THE TIME
OF ARRIVAL OF THE HEAVY PRECIP IS EXPECTED TO SHIFT AS WE MOVE
CLOSER TO THE EVENT.


.HYDROLOGICAL CONDITIONS...

ALL RIVERS WILL REMAIN NEAR CURRENT LEVELS FOR THE NEXT 2-3 DAYS.
PRECIPITATION FORECAST FOR THIS COMING WEEKEND WILL RESULT IN MODEST
RISES IN RIVERS LEVELS ALONG THE NORTHERN COAST OF CALIFORNIA AND IN
THE UPPER SACRAMENTO RIVER SYSTEM.

ALL RIVERS ARE CURRENTLY FORECAST TO REMAIN BELOW MONITOR LEVELS
THROUGH THE NEXT FIVE DAYS.


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

JM/KL/JM/PF

$$



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