Quantitative Precipitation Forecast
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FOUS30 KWBC 100058
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
757 PM EST MON JAN 09 2017

...VALID 01Z TUE JAN 10 2017 - 12Z TUE JAN 10 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
40 WNW CEC 45 NNW CEC 40 W SXT 30 SW SXT 40 E CEC 45 NE ACV
25 NW O54 25 WSW O54 40 SSW O54 30 ENE UKI 15 NE STS 20 W STS
45 SW UKI 65 W UKI.


...NORTHWEST CALIFORNIA...EXTREME SOUTHWEST OREGON...

IN THE WAKE OF THE MOST RECENT ATMOSPHERIC RIVER EVENT...RAINFALL
HAS TAPERED OFF FOR MOST OF CENTRAL AND ALL OF SOUTHERN
CALIFORNIA...HOWEVER THERE REMAINS AN AXIS OF PERSISTENT
POST-FRONTAL ONSHORE FLOW THAT IS BRINGING NUMEROUS SHOWERS INTO
NORTHERN CALIFORNIA WITH A PARTICULAR FOCUS ON THE COASTAL RANGES.
THE FLOW ALOFT IS RATHER STRONGLY DIFFLUENT AS WELL OUT AHEAD OF A
STRONG UPSTREAM 150+ KT JET MAX AT 250 MB. THIS IS AIDING LARGE
SCALE ASCENT AND COUPLING WITH THE DEEP LAYER WESTERLY ONSHORE
FLOW TO ENHANCE THE SHOWER ACTIVITY. ADDITIONALLY...THE LATEST
IR/WV SATELLITE IMAGERY SHOWS THERE IS A WELL-DEFINED SHORTWAVE
IMPULSE BEGINNING TO CROSS INTO NORTHWEST CALIFORNIA AND SOUTHWEST
OREGON. THIS FOCUSED ENERGY IS ACTUALLY FOCUSING SOME WELL-DEFINED
CONVECTION JUST OFFSHORE WITH SOME OF IT NOW CROSSING THE
NORTHWEST CALIFORNIA COASTAL RANGES INVOLVING DEL NORTE AND
HUMBOLDT COUNTIES. RAINFALL RATES OVERALL ARE NOT PARTICULARLY
HIGH FOR NOW GIVEN THE LACK OF DEEPER MID AND UPPER LEVEL
MOISTURE...BUT THE MOIST LOW LEVELS AND FAVORABLE LAPSE RATE
ENVIRONMENT IS SUCH THAT LOCALLY HEAVY RAINS WILL BE EXPECTED ON
OCCASION WITH THE CONVECTIVE ELEMENTS.

OVERNIGHT THERE WILL BE A PERSISTENT FEED OF MOISTURE AND ENERGY
IMPACTING NORTHERN CALIFORNIA AND FAR SOUTHWEST OREGON THAT WILL
MAINTAIN THE SHOWER ACTIVITY...BUT TOWARD DAWN THERE WILL BE THE
APPROACH OF A NEW SURGE OF DEEPER PACIFIC MOISTURE AND JET ENERGY
THAT WILL INCREASE THE COVERAGE AND INTENSITY OF PRECIPITATION.
THE MAIN CONCERN FOR ADDITIONAL HEAVY RAINS THROUGH 12Z WILL BE
FOR THE COASTAL RANGES...WITH AS MUCH AS 1 TO 2 INCHES OF
ADDITIONAL RAIN EXPECTED. MEANWHILE FARTHER EAST INTO THE CENTRAL
AND ESPECIALLY NORTHERN SIERRA-NEVADA...PRECIPITATION WILL BE
INCREASING BETWEEN 06Z AND 12Z...BUT THE ARRIVAL OF COLDER AIR IN
THE WAKE OF THE MOST RECENT STORM AND SUBSEQUENT LOWERING OF SNOW
LEVELS IS SUCH THAT MUCH OF THE HEAVIER PRECIPITATION HERE WILL BE
IN THE FORM OF SNOW OVERNIGHT. THEREFORE THE EXCESSIVE RAINFALL
OUTLOOK AT THIS TIME ONLY HIGHLIGHTS THE NORTHWEST CALIFORNIA AND
EXTREME SOUTHWEST OREGON COASTAL RANGES.

ORRISON
$$





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