AGUS76 KRSA 131722
HMDRSA

HYDROMETEOROLOGICAL DISCUSSION
NATIONAL WEATHER SERVICE / CALIFORNIA NEVADA RFC / SACRAMENTO CA
920 AM PST MON FEB 13 2012

...MODERATE PRECIPITATION INTO THE CENTRAL/SRN SIERRA NEVADA TODAY 
AND ACROSS CENTRAL NEVADA...
...A DRIER SYSTEM LATE TUE/WED WILL BRING PRECIPITATION MAINLY TO 
THE SIERRA NEVADA AND EAST ACROSS NV AND REACHING SRN CA...
...ANOTHER WEAK SYSTEM AFFECTING THE CNRFC AREA LATE FRIDAY AND INTO 
THE WEEKEND...

.24 HOUR PRECIPITATION TOTALS (ENDING FEB 13 AT 400 AM PST)...

A FEW AREAS OF LIGHT PRECIPITATION OCCURRED IN SRN CA AND ERN NV ON 
SUN BEHIND A TROUGH MOVING INTO THE GREAT BASIN.  AMOUNTS WERE 
GENERALLY 0.1" OR LESS WITH A FEW FEW LOCATIONS REPORTING 0.1-0.2" 
IN FAR ERN NV.

IN ADDITION...AN UPPER-LEVEL LOW PRESSURE SYSTEM AND ASSOCIATED COLD 
FRONT MOVED INTO NRN CA AND BROUGHT PRECIPITATION TO NRN AND CNTRL 
CA AND NV AS WELL AS SRN OREGON.  HEAVIEST AMOUNTS ON THE NORTH 
COAST WERE 0.5-1.6" IN THE MAD RIVER AND EEL BASINS AND NEAR CAPE 
MENDOCINO...WITH 0.2-0.5" FURTHER NORTH INTO THE SMITH AND ALSO 
SOUTH INTO THE RUSSIAN/NAPA BASINS.  TOTALS WERE GENERALLY 0.2" OR 
LESS IN THE SANTA CRUZ AND NRN SANTA LUCIA MTNS.  INTO THE CNTRL 
VALLEY...TOTALS RANGED FROM A FEW HUNDREDTHS IN THE NRN SAN JOAQUIN 
VALLEY TO 0.25-0.5" IN THE SRN HALF OF THE SACRAMENTO VALLEY AND 
0.5-1" FURTHER NORTH.  AMOUNTS AROUND THE LAKE SHASTA REGION WERE 
0.3-0.5"...WITH 0.1-0.4" IN FAR NRN AND NE CA...AS WELL AS SRN 
OREGON.  ABOUT 0.75-1.5" WAS REPORTED ON THE WEST SLOPES OF THE 
SIERRA FROM AROUND I-80 NWD...WITH 0.5-0.75" SWD TO HWY 4...AND 
GENERALLY 0.33" OR LESS THE REMAINDER OF THE SIERRA RANGE.  
LOCATIONS ON THE EAST SIDE OF THE SIERRA GENERALLY REPORTED ONLY 
0.2" OR LESS...WITH GENERALLY A FEW HUNDREDTHS OF AN INCH IN WRN AND 
CNTRL NV EXCEPT UP TO 0.2" IN THE HIGHER TERRAIN IN THE CNTRL PART 
OF THE STATE.


.METEOROLOGICAL CONDITIONS...

THE COLD UPPER LOW DROPPED INTO NORTHERN CALIFORNIA OVERNIGHT WITH 
SATELLITE SHOWING THE UPPER LOW NEAR THE CENTRAL SIERRA NEVADA 
CURRENTLY. SO FAR THIS SYSTEM HAS BEEN ON THE WETTER SIDE OF THE 
MODEL GUIDANCE AND EXPECT THAT TO CONTINUE THRU TODAY. THIS WILL 
TEND TO SHIFT THE HEAVIER PRECIPITATION FARTHER DOWN THE CENTRAL/SRN 
SIERRA NEVADA THIS MORNING AND EXPAND ACROSS CENTRAL NEVADA WHERE 
MODELS INDICATE SOME OF THE HEAVIER PRECIPITATION WILL DEVELOP LATER 
THIS AFTN/EVE WITH FAVORABLE DYNAMICS ASSOCIATED WITH SFC LOW 
CONVERGENCE AND UPPER DIVERGENCE AHEAD OF THE UPPER TROUGH AND 
INSTABILITY FROM THE COLD AIR ALOFT.  SNOW LEVELS LOOK TO BE AROUND 
4,000 FEET IN THE NRN SIERRA NEVADA AND EXPECT THESE TO LOWER AS THE 
COLDER AIR IS JUST ARRIVING.  AS THE UPPER LOW TRACKS SEWD REACHING 
SRN NV BY LATER THIS EVENING...NORTHERLY FLOW ON THE BACKSIDE OF THE 
LOW WILL TAPER PRECIPITATION QUICKLY FROM NORTH TO SOUTH TODAY  
BECOMING MOSTLY DRY BY 18UTC TUE MORNING FOR ALL BUT EXTREME ERN 
NEVADA WHERE LIGHT PRECIPITATION WILL LINGER INTO THE AFTN ALONG THE 
NV/UT BORDER.

FOLLOWING SEVERAL DAYS OF GREAT UNCERTAINTY IN THE MED/LONG RANGE 
AND ONLY FINDING SOME AGREEMENT SUNDAY IN THE 12UTC MODELS 
RUNS...THAT AGREEMENT HAS LARGELY HELD TOGETHER..GENERALLY FOLLOWING 
THE 00UTC GFS/ECMWF/GEM MODELS LEADING TO BETTER CONFIDENCE OF 
ANOTHER SYSTEM DROPPING INTO THE REGION FROM OREGON BY LATE TUE. 
WITH DRY ORIGINS AND AN INLAND TRACK TOWARDS SRN CA..THIS SYSTEM 
WILL BE GENERALLY ON THE DRIER SIDE WITH LIGHT PRECIPITATION 
BEGINNING ALONG THE NRN FRINGE OF THE CNRFC AREA LATE TUESDAY AND 
TRACKING SOUTHWARD ALONG THE CREST OF THE SIERRA NEVADA ENDING UP 
WITH SOME LIGHT AMOUNTS OVER SRN CA BY WED AFTN/EVE.  

ANOTHER TROUGH ENTERS THE PICTURE FROM THE NW AND SPREADS MORE LIGHT 
PRECIPITATION INTO NW CA TOWARDS EARLY SATURDAY. LIGHT PRECIPITATION 
WILL OVERTAKE MOST OF NRN CA BY SAT EVE AND QPF FOLLOWED A BLEND OF 
00UTC GFS/ECMWF. 


.HYDROLOGICAL CONDITIONS...

RUNOFF FROM THE CURRENT WEATHER SYSTEM IS EXPECTED TO PRODUCE SLIGHT 
TO MINOR RISES TO MANY RIVERS AND STREAMS IN CALIFORNIAS COASTAL AND 
CENTRAL VALLEY WATERSHEDS.  

NO APPRECIABLE RISES ARE EXPECTED FROM THE WX SYSTEM FORECAST TO 
ARRIVE IN THE REGION BY LATE TUESDAY.

ALL RIVER FORECAST POINTS ARE EXPECTED TO REMAIN BELOW MONITOR 
LEVELS FOR THE NEXT SEVERAL DAYS.


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

KL/ME/AT

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