Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 060044
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
843 PM EDT THU MAY 05 2016

...VALID 01Z FRI MAY 06 2016 - 12Z FRI MAY 06 2016...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


01Z UPDATE...

...NORTH CAROLINA/SE VIRGINIA...

PCPN MODE ACRS THE THE CAROLINAS AND SRN VA HAS GONE TO MORE OF A
STRATIFORM REGIME AS NARROW ZONE OF WEAK INSTABILITY HAS MOVED OFF
THE NC COAST.  RAINS WILL CONTINUE TO INCREASE THRU PARTS OF
ERN/CNTL NC INTO ERN VA OVERNIGHT IN THE EVOLVING COMMA HEAD BAND
AS RATHER INTENSE UPR LOW SWINGS NEWD INTO ERN NC/SE VA BY FRI
MRNG. SOME BANDED HEAVIER RAIN ELEMENTS ARE LIKELY WITHIN THE
COMMA HEAD BAND WITHIN INCREASING 85H/7H THEATAE ADV/CONFLUENCE
ZONE BUT THE MAIN THREAT OF THE HEAVIER RAINS WILL MORE LIKELY BE
LOCALIZED PONDING OF WATER THAN FLASH FLOODS GIVEN LACK OF
INSTABILITY.  SOME ISOLD 6 HR TOTALS UP TO AN INCH OR SO WILL BE
POSSIBLE ACRS SE VA/NE NC.

ELSEWHERE...NO CHANGE TO THE SEE TEXT AREAS ACRS NORTHERN
CALIFORNIA AND EASTERN OREGON.   SEE MPD#179 VALID UNTIL 06/0230Z
FOR FURTHER DETAILS.


...NORTHERN CALIFORNIA...

GIVEN A SUPPORTIVE MODEL QPF SIGNAL...THERE IS SOME CONCERN OVER
SLOW MOVING CONVECTIVE CELLS LATER TODAY WITHIN A LIGHT LOWER TO
MIDDLE LEVEL FLOW REGIME OVER NORTHERN CALIFORNIA. MEAN 0-6 KM
WINDS OF ZERO TO TEN KNOTS COINCIDE WITH MOST UNSTABLE CAPE VALUES
OF 500 J/KG OR MORE IN THE SACRAMENTO VALLEY AND ADJACENT MOUNTAIN
AREAS INCLUDING THE SIERRAS AND SHASTAS. HIGH RESOLUTION MODELS
GENERALLY PREDICT SPOTTY HALF INCH PER HOUR RATES...WHICH WOULD
FALL SHORT OF FLASH FLOOD GUIDANCE...BUT THE VERY SLOW CELL MOTION
AND POTENTIAL CELL MERGERS COULD EASILY RESULT IN OBSERVED
ACCUMULATIONS OVER ONE INCH IN AN HOUR GIVEN THE SOMEWHAT
ANOMALOUSLY HIGH PRECIPITABLE WATER VALUES IN THE NEIGHBORHOOD OF
0.80 INCHES. MANY OF THE HI-RES MODELS PREDICT SPOT EVENT TOTALS
GREATER THAN 1.5 INCHES THROUGHOUT NORTHERN CALIFORNIA THROUGH
THURSDAY NIGHT.


...EASTERN OREGON...

WITHIN DEEP SOUTHERLY MIDDLE AND UPPER LEVEL FLOW...A SHORTWAVE
RIDGE WILL PUSH DOWNSTREAM INTO MT/ID THIS AFTERNOON...OPENING UP
A MORE DIFLUENT PATTERN OVER EASTERN OREGON...AND OVERLAPPING WITH
A SLOPING BAROCLINIC ZONE TO THE WEST OF A SURFACE FRONT. WITH A
JET STREAK ROUNDING THE EAST SIDE OF THE UPPER LOW IN
CALIFORNIA...DEEP LAYER ASCENT WILL INCREASE ACROSS EASTERN
OREGON...WITH THE GFS DEPICTING PRONOUNCED 700 MB FRONTOGENESIS
AND INCREASING STRENGTH TO THE 850-700 MB SOUTHEASTERLY INFLOW.
THE MODEL QPF SIGNAL OVER OREGON IS SIMILAR TO THAT OVER NORTHERN
CALIFORNIA...SEE SECTION ABOVE. CELL MOTIONS WILL NOT BE AS
SLOW...BUT THE PATTERN IS SET UP FOR BRIEF SSE-NNW TRAINING OF
ECHOES...AND GREATER INFLOW INTO THIS REGION WILL AIDE GENERATION
OF NEW UPDRAFTS ALONG OUTFLOWS.

HURLEY/BURKE/SULLIVAN
$$





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