Quantitative Precipitation Forecast
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FOUS30 KWBC 290059
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
859 PM EDT THU JUL 28 2016

...VALID 01Z FRI JUL 29 2016 - 12Z FRI JUL 29 2016...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 SSE WAL 15 NNE NTU FKN 10 NE AVC 20 ESE LYH 20 SSW SHD
15 SW JYO DOV 20 SE WWD 10 ENE OXB 15 SSE WAL.



...MID ATLANTIC TO SOUTHERN NY AND SOUTHERN NEW ENGLAND...

0100 UTC UPDATE...HAVE BEEN ABLE TO CONFINE THE PREVIOUS SLIGHT
RISK AREA TO EASTERN VA... SOUTHERN MD...AND MUCH OF THE
DELMARVA...BASICALLY WHERE THE DEEP-LAYER CAPE IS SUFFICIENT TO
MAINTAIN THE POTENTIAL OF EXCESSIVE SHORT TERM RAINFALL RATES. THE
EVOLVING CONVECTIVE PATTERN LATE IN THE AFTERNOON AHEAD OF THE
BROAD UPPER TROUGH HAD QUICKLY WORKED OVER THE AVAILABLE
INSTABILITY FARTHER NORTH OF THE OUTLOOK AREA...WHICH IS NOTED PER
THE LATEST IR LOOPS BY THE DISTINCTLY WARMER CLOUD TOPS WITHIN THE
NORTHERN PORTION OF THE WARM CONVEYOR BELT (N OF THE MID LEVEL
INFLECTION POINT). THE LATEST HIGH-RES GUIDANCE NEVERTHELESS
CONTINUES TO SHOW THE POSSIBILITY OF A SECONDARY RAINFALL MAX
ACROSS SOUTHERN PORTIONS OF THE NORTHEAST-SOUTHERN NEW
ENGLAND...DESPITE THE MARGINAL INSTABILITY (MUCAPES 1000-1500
J/KG)...GIVEN THE SHARP UPTICK IN 850-700 MB WAA AND MOISTURE FLUX
OVERNIGHT (AS PWS CLIMB TO 2-2.25") WHILE DYNAMICAL FORCING
BECOMES QUITE FAVORABLE AS DPVA AHEAD OF THE TROUGH COMBINES WITH
INCREASING FRONTOGENETIC FORCING VIA THE RIGHT ENTRANCE REGION OF
THE UPPER JET STREAK TO THE NORTHEAST (COUPLED FORCING).
STILL...GIVEN THE LACK OF INSTABILITY IN THIS AREA...EXPECT MORE
OF A MARGINAL OR ISOLATED FLASH FLOOD THREAT.

HURLEY


PREVIOUS DISCUSSION BELOW...

FLASH FLOOD POTENTIAL EXISTS OVER A BROAD AREA TODAY...ALTHOUGH
THE OVERLAY OF MOISTURE / LIFT / INSTABILITY DOES NOT IMMEDIATELY
POINT TOWARD ONE AREA BEING AT GREATER RISK THAN ANOTHER. THE QPF
SIGNAL IS ALSO SOMEWHAT VARIABLE...BUT ALL SOLUTIONS POINT TOWARD
HEAVY AREAL AVERAGE PRECIPITATION FROM EASTERN TN/KY INTO WV AND
SOUTHERN OH...AND MANY SOLUTIONS ALSO POINT TOWARD THE MASON-DIXON
LINE AND 50 MILES TO EITHER SIDE AS A SECOND AXIS OF HEAVY RAIN.

RICH MOISTURE WILL BE SWEPT UP AHEAD OF AN ADVANCING TROUGH...WITH
WIDESPREAD PRECIPITABLE WATER VALUES NEAR/ABOVE 2.0 INCHES RUNNING
ABOUT 2 STANDARD DEVIATIONS ABOVE CLIMATOLOGY. THE TROUGH WAS SET
TO JOIN THE WESTERLIES...WITH SOME ACCELERATION EXPECTED TODAY.
THIS WILL INCREASE THE STRENGTH OF SOUTHWESTERLY LOWER LEVEL FLOW
INTO THE EASTERN TN/OH VALLEYS AND INTO THE UPSLOPE AREAS OF THE
CENTRAL APPALACHIANS. AT THE SAME TIME...FORCING SPILLS OVER INTO
THE MID ATLANTIC...INCLUDING MUCH OF SOUTHERN PA DOWN THROUGH
VA/MD AND EASTWARD...AS MID/UPPER SUPPORT IS ENHANCED WITHIN THE
ENTRANCE REGION OF A DEVELOPING JET STREAK. FORECAST SOUNDINGS
INDICATE A LOT OF HIGH CLOUDINESS WHICH MAY LIMIT INSTABILITY
ALONG THE PATH OF GREATEST FORCING FOR ASCENT...BUT THE LIFT
ITSELF WILL OPERATE ON A DEEPLY SATURATED ENVIRONMENT...AND EVEN
MINIMAL INSTABILITY WOULD BE ENOUGH TO LEAD TO SOME EFFICIENT
RAINFALL PROCESSES. HEAVIER SHORT TERM RAIN RATES ARE POSSIBLE A
LITTLE FARTHER SOUTH IN AREAS OF GREATER HEATING FROM EASTERN TN
INTO VA/MD/DE...ESPECIALLY EAST THROUGH NORTHEAST OF LOW PRESSURE
SETTING UP NEAR I-95 D.C. TO BALTIMORE. ADDITIONALLY...A FEW
SOLUTIONS POINT TOWARD A REDEVELOPMENT OF HEAVY RAIN OVER
SOUTHWEST PA THURSDAY NIGHT IN THE DEFORMATION AREA OF WHATEVER
CIRCULATION MAY CONTINUE TO EXIST EMBEDDED WITHIN THE ADVANCING
TROUGH. THUS THE HEAVY RAIN THREAT MAY PERSIST
OVERNIGHT...ESPECIALLY FROM PA EASTWARD INTO NJ/NY.


...CENTRAL TO SOUTHERN PLAINS...

THE PARAMETERS ARE FAIRLY WELL DEFINED WHICH WILL ALLOW FOR AN
ACTIVE PERIOD OF THUNDERSTORMS WITHIN A WNW FLOW REGIME ACROSS THE
CENTRAL PLAINS STATES CENTERING ON KANSAS. RECENTLY ARRIVED
FRONTAL BOUNDARIES WILL FOCUS THE WESTWARD PUSH OF DEEPER MOISTURE
INTO THE CENTRAL HIGH PLAINS...AND PHASING OF SHORTWAVE ENERGY
COMING DOWN OUT OF MONTANA AND THE DAKOTAS WILL PROVIDE THE
IMPETUS FOR SCATTERED TO NUMEROUS THUNDERSTORMS. THE SHEAR IS
STRONG ENOUGH TO ALLOW FOR SUPER CELLS AND A FORWARD PROPAGATING
SYSTEM OR SYSTEMS. THE REGIME LOOKS TYPICAL OF THE PLAINS...WITH
FLASH FLOOD POTENTIAL TIED MAINLY TO THE EARLY STAGES OF
DEVELOPMENT PRIOR TO FORWARD PROPAGATION AND/OR CELL MERGERS
DURING UPSCALE GROWTH. ANTECEDENT CONDITIONS ARE NOT PARTICULARLY
WET...BUT SOME PARTS OF WESTERN KS HAD RECEIVED ABOVE AVERAGE
RAINFALL IN THE PAST SEVEN DAYS...AND SLIGHTLY ANOMALOUS MOISTURE
CONTENT WILL ALLOW FOR HEAVY RAIN RATES CAPABLE OF EXCEEDING FLASH
FLOOD GUIDANCE VALUES.


...LOWER MISSISSIPPI VALLEY...

BEHIND THE DEPARTING TROUGH THAT WILL BE MOVING TOWARD THE
APPALACHIANS...THERE WILL BE A PERIOD OF CONVERGENT / CONFLUENT
LOWER LEVEL FLOW INTO PARTS OF EAST TEXAS INTO AR/LA AND PERHAPS
ADJACENT TN/MS. MODELS INDICATE POTENTIAL FOR HEAVIER RAINFALL IN
THIS REGION...ESPECIALLY DURING THE MORNING HOURS. WITH RICH
MOISTURE IN PLACE AND POTENTIAL FOR WEST TO EAST TRAINING...A FEW
LOCATIONS COULD EXPERIENCE RAINFALL EXCEEDING FLASH FLOOD GUIDANCE
VALUES. FFG HAD BEEN LOWERED LOCALLY BY HEAVY RAIN THAT OCCURRED
WEDNESDAY.

BURKE
$$





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