Quantitative Precipitation Forecast
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FOUS30 KWBC 200831
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
430 AM EDT FRI MAY 20 2016

...VALID 12Z FRI MAY 20 2016 - 12Z SAT MAY 21 2016...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 W FTK 10 S VTA 10 E MGW 10 ENE OFP 15 NW ASJ 10 NW HRJ
10 ESE MWK BLF 40 NNE LNP 20 SSW 1A6 20 ENE 4A9 15 SW DCU
55 WSW BNA 15 W FTK.


...TENNESSEE AND KENTUCKY INTO PARTS OF OH/WV/VA/NC...

A RELATIVE MAXIMUM SWATH OF RAINFALL IS FORECASTINTO NORTHERN
TN/CENTRAL KY...GENERALLY FROM NASHVILLE TO
LEXINGTON. THE MODEL GUIDANCE WAS ABSOLUTELY UNANIMOUS IN THIS
ASPECT. GLOBAL AND MESOSCALE MODELS ALIKE APPEAR TO BE LATCHING
ONTO MODERATE SYNOPTIC FORCING WHERE SOME SENSE OF UPPER JET
COUPLING COINCIDES WITH A FEED OF SEASONABLY MOIST AND
SUFFICIENTLY UNSTABLE AIR. THE CONVERGENT NORTHERN EXTENT OF A LOW
LEVEL JET IS FORECAST TO TRACK STEADILY ALONG A PATH FROM
WESTERN/NORTHERN TN INTO CENTRAL KY AND SOUTHERN OH. MODELS
GENERALLY AGREE TO 1 TO 2 INCH AREAL AVERAGE RAINFALL ALONG THIS
SWATH...WHILE THEIR FORECASTS HAVE DRIED
CONSIDERABLY OVER EASTERN TN...PERHAPS OWING BOTH TO CHANGES IN
ASCENT AND SOME MOISTURE ROBBING ASPECT OF THE GULF COAST
CONVECTION. FARTHER EAST THE FORECAST IS MORE STABLE...WITH
PRECIPITATION SURROUNDING A COASTAL LOW POISED TO AFFECT COASTAL
PARTS OF THE CAROLINAS...AND ADDITIONAL RAINFALL...SOME
CONVECTIVE...BREAKING OUT FROM THE MOUNTAINS TOWARD THE
PIEDMONT/COASTAL PLAIN IN NC/VA AS WELL DEFINED SYNOPTIC FORCING
OVERSPREADS THE REGION THIS EVENING/TONIGHT. GIVEN A SEASONABLY
MOIST AIRMASS...WITH INSTABILITY AT THE HIGH END OF LOW OR LOW END
OF MODERATE...FLASH FLOODING APPEARS POSSIBLE...AT LEAST LOCALLY.


...GEORGIA AND SOUTH CAROLINA...

A WELL FORMED BOW ECHO WITH IMPRESSIVE RADAR PRESENTATION WAS
TRACKING ALONG THE GULF COAST AT 08Z. THE BROAD MESOSCALE
CONVECTIVE VORTEX ASSOCIATED WITH THIS WAS LOCATED INLAND...AND
MEAN STEERING FLOW IN THE 600-400 MB LAYER SHOULD GUIDE THE MCV
TOWARD SOUTHERN/CENTRAL GEORGIA AND WESTERN SOUTH CAROLINA BY
AFTERNOON. NONE OF THE HI-RES MODELS IS HANDLING THIS
IDEALLY...ALTHOUGH ALL HAVE A HEAVY RAINFALL SIGNAL SCATTERED
AROUND THE SOUTHEAST U.S...AND ALL SHOW VARYING EVOLUTION AND
TIMING. WE HAVE TAKEN THE APPROACH OF EXTRAPOLATING FROM
OBSERVATIONAL TRENDS...SUGGESTING THAT THE MOST LIKELY SCENARIO TO
PRODUCE A FLASH FLOOD CONCERN WOULD BE RENEWED AFTERNOON/EVENING
CONVECTION FORCED AHEAD OF THE MCV AND NORTH OF A QUASI-STATIONARY
FRONT WHERE EASTERLY LOW LEVEL WINDS WILL PROVIDE INFLOW OF VERY
MOIST AIR...WITH PW ABOVE 1.50 INCHES. THOUGH FLASH FLOOD GUIDANCE
NUMBERS ARE HIGH...RAIN RATES COULD EXCEED 2 INCHES PER HOUR...AND
CELL MERGERS/ORGANIZATION COULD BOOST 3-HOUR TOTALS OVER FFG.
CONFIDENCE IN THE SCENARIO IS ONLY MODEST...HOWEVER...SO WILL NOT
INTRODUCE A RISK AREA AT THIS TIME.


...NORTHERN CALIFORNIA...

SLOW CELL MOTIONS AND SUFFICIENT MOISTURE BENEATH A COLD UPPER LOW
MAY LEAD TO AN ISOLATED FLASH FLOOD CONCERN IN THE WESTERN
FOOTHILLS OF THE HIGH SIERRAS.


...NORTHERN MONTANA...

SHOULD AN MCS BECOME ESTABLISHED NEAR THE INTERNATIONAL
BORDER...EAST OF THE MOUNTAINS...INFLOW WILL BE STRONG THIS
EVENING/OVERNIGHT...SUPPORTING A MENTIONABLE RISK OF EXCESSIVE
RAINFALL. CONFIDENCE IN THE DETAILS IS LOW...HOWEVER.


BURKE
$$





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