Hydrometeorological Discussion
Issued by NWS California-Nevada RFC

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HYDROMETEOROLOGICAL DISCUSSION NATIONAL WEATHER SERVICE / CALIFORNIA
NEVADA RFC / SACRAMENTO CA 955 AM PDT MON OCT 20 2014

***** REISSUANCE TO MODIFY HYROLOGICAL DISCUSSION *****

...COLD FRONT MOVING THRU NORTHERN HALF OF REGION TODAY INTO TUE...
...MODERATE TO HEAVY PRECIP NORTH OF I-80 LATTER HALF OF THE WEEK...

.24 HOUR PRECIPITATION TOTALS (ENDING OCT 20 AT 500 AM PDT)...

PRECIP BEGAN FALLING SHORTLY BEFORE MIDNIGHT LAST NIGHT ON THE NORTH
COAST AS A FRONT MOVED INTO THE AREA AHEAD OF AN UPPER TROUGH
CURRENTLY CENTERED OVER 130W. PRECIP AMOUNTS WERE HIGHEST OVER THE
NW CORNER OF THE STATE IN THE SMITH BASIN...WHERE 1-2" FELL PRIOR TO
5 AM THIS MORNING. AMOUNTS FELL TO AROUND 0.3-0.6" OVER THE EEL R
BASIN...AS WELL AS EAST OF THE SMITH INTO THE TRINITY MTNS. LESS
THAN 0.1" HAD ACCUMULATED IN THE RUSSIAN R BASIN PRIOR TO 5 AM.
FURTHER NORTH AND INLAND OVER THE UPPER KLAMATH...0.2-0.4" PRECIP
FELL ALONG THE WEST SLOPES OF THE SRN OREGON CASCADES...WITH NOTHING
BREACHING THE CREST THUS FAR.


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

WV/IR IMAGERY SHOWS THE NEXT S/WV TROF MOVING WITHIN 130W WHILE THE
ASSOCIATED COLD FRONT IS MOVING ONSHORE ALONG THE NORTH COAST THIS
MORNING. PRECIP SHIELD AHEAD OF THE FRONTAL BOUNDARY IS FAIRLY
NARROW WITH THE LEADING EDGE STRETCHING FROM THE CREST OF THE
SOUTHERN OREGON CASCADES SOUTH ACROSS THE SHASTA LAKE DRAINAGE AND
ALONG THE COASTAL MOUNTAINS BEFORE MOVING OFFSHORE NEAR THE GOLDEN
GATE. THERE IS A DECENT AMOUNT OF MOISTURE ENTRAINED INTO THE SYSTEM
CONVERGING JUST AHEAD OF THE COLD FRONT. GPS-MET SENSORS ALONG THE
NORTH COAST SHOWED IPW VALUES PEAKING AROUND 1.25-INCH. BLENDED TPW
IMAGERY SHOWS THE MOISTURE PLUME MOVING ONSHORE ALONG THE NORTH
COAST WITH THE COLD FRONT AND THEN TRAILING OFF TOWARD THE SW BACK
TO THE LOWER LATITUDES.

THROUGH THE REST OF THE MORNING INTO THE AFTERNOON HOURS...LOOK FOR
THE COLD FRONT TO PROGRESS SOUTH AND INLAND TO THE SIERRA BACK
THROUGH THE SF BAY AREA. MEANWHILE...THE S/WV TROF AXIS WILL ARRIVE
AT THE COAST AROUND 21/00Z. THE MAJORITY OF THE PRECIP WILL FALL
WITH THE FRONTAL BAND...BUT THE MODELS INDICATE LIGHT PRECIP WITH
THE COOLER AIR ALOFT NEAR THE S/WV TROF. OVERNIGHT...PRECIP WILL
SHIFT TO NORTHERN NEVADA...BUT HERE THE PRECIP WILL BE MORE
ASSOCIATED WITH THE S/WV TROF MOVING THROUGH THE AREA. BY LATER
TUESDAY MORNING INTO THE AFTERNOON HOURS...THE S/WV TROF WILL EXIT
THE AREA TO THE NE ON ITS WAY TO THE NORTHERN ROCKIES.

FOR LATER TUESDAY INTO WEDNESDAY...THE FLOW ALOFT TURNS WESTERLY
ACROSS THE PACIFIC AT THE MID-LATITUDES. WITH A DEEP VORTEX OVER THE
GULF OF ALASKA AND A SUBTROPICAL HIGH PRESSURE RIDGE CENTERED JUST
EAST OF THE HAWAIIAN ISLANDS...THE UPR JET WILL STRENGTHEN ALONG 40N
WITH WINDS AT THE 300-MB LEVEL REACHING NEAR 155-KT ACCORDING TO THE
LATEST EC (20/00Z) AND GFS (20/06Z). A MOISTURE PLUME WILL RIDE EAST
ALONG THIS FLOW AT 40N...AFTER ADVECTING NORTH FROM THE LOWER
LATITUDES NEAR AND JUST WEST OF THE INT/L DATELINE. FOR
WEDNESDAY...THE MODELS ARE IN RELATIVELY GOOD AGREEMENT INITIALLY
TAKING THE MOISTURE PLUME INTO THE PACNW BEFORE SINKING SOUTH AND
AFFECTING THE UPPER KLAMATH RIVER BASIN AND FAR NW CA. WITH BETTER
AGREEMENT ON DAY 3...CONFIDENCE IS BETTER WITH THE MODERATE TO HEAVY
PRECIP AMOUNTS...ESPECIALLY THE SECOND HALF OF THE DAY. WINDS AT THE
850-MB LEVEL ARE SWLY IN THE 40- TO 50-KT RANGE WITH PW VALUES NEAR
1.50-INCHES INTERSECTING THE COAST. ISENTROPIC LIFT AHEAD OF THE
BAROCLINIC ZONE LOOKS MOST IDEAL BETWEEN THE 305- AND 310-K
SURFACES...WHILE CONDENSATION PRESSURE DEFICITS EASILY DROP UNDER 10-
MB. THE 12-HOUR PERIOD ENDING THURSDAY MORNING (23/12Z) WILL BE
WETTEST OVER THE SMITH RIVER BASIN WITH 1.50- TO ALMOST 3.00-INCHES
POSSIBLE.


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

THE FRONT IS EXPECTED TO CONTINUE MOVING THROUGH NORTHERN CA
THURSDAY MORNING...BRINGING MODERATE TO HEAVY PRECIP TO MUCH OF
COASTAL NORTHERN CA THROUGH THE DAY. MODELS DROP THE FRONT AS FAR
SOUTH AS THE RUSSIAN BASIN AND NORTHEAST THROUGH THE SACRAMENTO
VALLEY INTO THE NORTHERN SIERRA AND THE NW CORNER OF NEVADA BY
AFTERNOON. AFTER THIS POINT...SIGNIFICANT DIFFERENCES ARISE BETWEEN
THE GFS...EC...AND GEM MODELS THROUGH THE REMAINDER OF THE PERIOD.

TIMING...TRACK...AND INTENSITY ALL FALL OUT OF AGREEMENT FOR THE
LAST DAY AND A HALF OF THE FORECAST PERIOD. THE 20/06Z GFS
STRENGTHENS AND STALLS THE FRONT OUT OVER SONOMA AND MENDOCINO
COUNTIES THURSDAY NIGHT INTO FRIDAY...BRINGING A PROLONGED PERIOD OF
HEAVY PRECIP TO THE AREA. MEANWHILE...A SECOND WAVE OF PRECIP
DEVELOPS JUST AHEAD OF THE TROUGH...BRINGING MODERATE PRECIP TO THE
NORTH COAST FRIDAY NIGHT AND MOVING INTO THE REST OF NORTHERN CA
OVERNIGHT INTO SATURDAY MORNING. THE TROUGH FINALLY COMES ONSHORE
LATER IN THE DAY SATURDAY...BRINGING SCATTERED SHOWERS TO MUCH OF
THE NORTHERN HALF OF CA AND NRN NEVADA THROUGH SUNDAY NIGHT BEFORE
PUSHING EAST. THE 20/00Z ECMWF TAKES A MORE MODERATE APPROACH...
WASHING OUT THE FRONT ON THURSDAY THROUGH MENDOCINO COUNTY AND
DRYING OUT MUCH OF THE AREA BEFORE A SECOND WAVE MOVES IN FRIDAY
NIGHT. THIS SECOND WAVE IS MUCH MORE MODERATE THAN THE SECOND THE
GFS PULLS THROUGH...BUT DOES STILL COVER MUCH OF THE SAME AREA. A
THIRD AND FINAL WAVE QUICKLY PASSES THROUGH AS THE TROUGH MOVES INTO
NORTHERN CA SATURDAY NIGHT...AND MOVES EAST...AGAIN LEAVING THE
FORECAST AREA DRY BY SUNDAY MORNING. THE CANADIAN IS MOST SIMILAR TO
THE GFS...BUT BRINGS IN A MUCH HEAVIER FINAL WAVE TO THE NORTH COAST
SATURDAY NIGHT.

THE CURRENT FORECAST PACKAGE REFLECTS A BLEND OF THE COHESIVE GFS
AND EC MODELS THROUGH 00Z FRIDAY...THEN STEERS THE FORECAST IN THE
DIRECTION OF THE 20/00Z ECMWF FOR THE REMAINDER OF THE PERIOD. HAVE
TWEAKED SOME PRECIP AMOUNTS ABOVE THE MODEL GUIDANCE FOR THIS
PERIOD...AS IS TYPICALLY SEEN WITH SYSTEMS THAT FOLLOW THE EC.
EXPECT THE DETAILS TO CHANGE QUITE A BIT AS THE WEEK PROGRESSES AND
(HOPEFULLY) MODELS FIND A BETTER COMPROMISE.


.HYDROLOGICAL CONDITIONS...

VERY SMALL RISES TO NORTH COASTAL RIVERS AHD STREAMS ARE EXPECTED
FROM THE WEATHER SYSTEM CURRENTLY MOVING ACROSS NW CALIFORNIA.

COASTAL BASINS OF NORTHERN CALIFORNIA WILL SHOW THE MOST RESPONSE TO
PRECIPITATION FROM THE WEATHER SYSTEM ARRIVING BY WEDNESDAY...WITH
ONLY MINOR RISES EXPECTED...THE LARGEST OF THESE RISES WILL BE IN
THE SMITH RIVER BASIN.

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

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

JM/DRK/JM/AT

$$



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