RNOHMDRSA (05/05/09 0932)


AGUS76 KRSA 051631
HMDRSA

HYDROMETEOROLOGICAL DISCUSSION
NATIONAL WEATHER SERVICE / CALIFORNIA NEVADA RFC / SACRAMENTO CA
930 AM PDT TUE MAY 5 2009

...PRECIPITATION WINDING DOWN THIS AFTERNOON AND EVENING...
...ANOTHER LIGHTER SHOT OF PCPN MAINLY NORTH ON WEDNESDAY...

.24 HOUR PRECIPITATION TOTALS (ENDING MAY 5 AT 500 AM PDT)...

MEASURABLE PCPN WAS RECORDED ALONG AND N OF AN AREA FM MONTEREY BAY 
TO MONO LAKE.  THE HEAVIEST PCPN WAS OVER THE NRN CA COAST FM THE 
RUSSIAN BASIN NWD...EXTENDING INLAND TO THE AREA ABOVE LAKE SHASTA
AND INTO THE NRN SIERRA NV MTNS...WITH BASIN AMOUNTS GENERALLY 
1.0-2.0 INCHES...EXCEPT EXCEEDING 3.0 INCHES IN THE SMITH BASIN.  
OTHERWISE...0.25-0.50 INCH BASIN AMOUNTS WERE NOTED IN THE NAPA 
BASIN...THE SANTA CRUZ MTNS...THE NRN SAC VALLEY...AND IN THE AREA 
BETWEEN LAKE TAHOE AND THE YOSEMITE VALLEY.

.METEOROLOGICAL CONDITIONS...

THE LATEST WET SYSTEM TO HIT NRN CA HAS PUSHED A FRONTAL ZONE INTO 
CNTRL CA...WHILE THE LG SCALE UPPER SUPPORT HAS MOVED OFF TO THE 
EAST.  THE FLOW REMAINS ZONAL SO ONSHORE FLOW WILL CONTINUE TO HELP 
SQUEEZE OUT PCPN ALONG THE NRN CA COAST AND NRN SIERRA NV 
MTNS...HEAVIEST IN THE VICINITY OF THE DISSIPATING FNTL ZONE THAT 
EXTENDS FM AROUND MONTEREY BAY TO NR LAKE TAHOE.  

WEAK LG SCALE SUBSIDENCE WILL OVERSPREAD THE AREA TODAY AND THIS EVE 
WITH FLAT UPPER RIDGING.   ANOTHER LOW AMPLITUDE SYSTEM WILL IMPACT 
THE PAC NW AND NRN CA ON WED.  A MOISTURE PLUME WITH MAX VALUES 
OFFSHORE FCST TO EXCEED 1.25 INCHES WILL ACCOMPANY THIS NEXT SYS AND 
THE PLUME WILL PUSH INTO CNTRL CA BY WED AFTN (06/18Z) BEFORE 
DISSIPATING LATER IN THE DAY.  HOWEVER...THE STRONGEST LG SCALE 
ASCENT WILL BE OVER THE PAC NW WITH THIS SYS AND THE UPPER JET CORE 
WILL JUST SKIRT THE NRN BOUNDARY OF THE CNRFC.  THUS...PCPN AMOUNTS 
WILL BE MUCH LOWER THAN WITH THE RECENT WX SYSTEMS...AND PCPN WILL 
BE CONFINED TO THE NRN CNRFC AREA...MAINLY THE NRN CA COAST...WITH 
MEASURABLE PCPN NOT MAKING IT S OF I-80.  PCPN WILL TAPER OFF WED 
EVE AND THE AREA WILL DRY OUT AFTER THAT AS ZONAL FLOW 
CONTINUES...BUT GEOPOTENTIAL HEIGHTS INCREASE SOMEWHAT IN FLAT UPPER 
RIDGING. 

THE BIGGEST CHANGES TO THE HPC QPF WERE IN THE FIRST PD...WITH 
HEAVIER AMOUNTS FM CNTRL CA INTO THE LAKE TAHOE AREA ALREADY 
OCCURRING ABOVE THE HPC GUIDANCE.  OTHERWISE...DEPARTURES FM THE HPC 
QPF WERE MINIMAL.


DAY 1 QPF (TUE 05/12Z TO WED 06/12Z):  0.25 INCH BASIN AMTS FOR THE 
NRN SIERRA AND THE FAR NRN CA COAST...EXCEPT THE SMITH BASIN WHERE 
AMOUNTS WILL REACH NR 0.50 INCHES.  OTHERWISE...0.10-0.25 INCHES IN 
THE BASINS ABOVE LAKE SHASTA.   

DAY 2 QPF (WED 06/12Z TO THU 07/12Z):  0.25-0.50 INCH BASIN AMTS FOR 
THE NRN CA COAST FM THE EEL BASIN NWD INTO THE MAD...INCREASING TO 
0.50 INCHES IN THE LOWER KLAMATH AND AROUND 1.0 INCH IN THE SMITH.  
OTHERWISE...0.10-0.25 INCHES FOR THE BASINS ABOVE LAKE SHASTA AND 
THROUGH THE MIDDLE AND UPPER KLAMATH.  

DAY 3 QPF (THU 07/12Z TO FRI 08/12Z):  DRY.


.HYDROLOGICAL CONDITIONS...
THE RIVERS AND STREAMS OF NORTHERN CALIFORNIA AND WESTERN NEVADA 
PRODUCED MINOR RISES AS A RESULT OF THE RAINFALL THE PAST FEW DAYS.  
ALL FORECAST POINTS ARE EXPECTED TO REMAIN BELOW MONITOR LEVELS.

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

ASH/TLM