MESOSCALE PRECIPITATION DISCUSSION 0220
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
303 PM EDT SUN JUL 27 2014
 
AREAS AFFECTED...EASTERN OH/WESTERN PA/NORTHERN WV/MD PANHANDLE... 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 271902Z - 272302Z
 
SUMMARY...EARLY AFTERNOON HEATING HAS HELPED DEVELOP WIDESPREAD
SURFACE-BASED CONVECTION ACROSS THE OH VALLEY. WHILE FLASH
FLOODING IS NOT IMMINENT...GRADUAL ORGANIZATION IS EXPECTED AS
LOW-LEVEL WINDS BEGIN TO STRENGTHEN BY THE EARLY EVENING.

DISCUSSION...A DYNAMIC MID-LEVEL PATTERN IS IN PLACE ACROSS THE
REGION WITH AN 18Z RAOB FROM ILN SHOWING 50 TO 60 KNOTS OF FLOW
AROUND 500-MB. MID/UPPER LEVEL DRYING WAS NOTED IN THE WATER VAPOR
IMAGERY AS WELL AS WITH SPECIAL 18Z SOUNDINGS ACROSS THE OH
VALLEY/CENTRAL APPALACHIANS. HOWEVER...PLENTY OF MOISTURE IS IN
PLACE BELOW THIS SUB-SATURATED LAYER WITH PWATS REACHING THE 1.50
INCH MARK. ADDITIONALLY...THE GUIDANCE SHOWS LOW-LEVEL WARM
ADVECTION TRANSPORTING HIGHER MOISTURE FROM THE TN VALLEY INTO THE
OH VALLEY.

THE CURRENT RADAR IMAGERY SHOWED WIDESPREAD CONVECTION ACROSS THE
NORTHERN HALF OF OH WITH CELL MOTIONS GENERALLY AT 20 TO 30 KNOTS
TOWARD THE EAST. THE ENTIRE REGION IS UNCAPPED WITH 2000-3000 J/KG
OF SBCAPE PER AN 18Z OBJECTIVE ANALYSIS. SO THERE IS LITTLE REASON
TO BELIEVE THE CONVECTION WILL WANE DURING THE NEXT SEVERAL HOURS
WITH VERY HEAVY DOWNPOURS EXPECTED WITHIN THE STORMS SUSTAINING
STRONGER UPDRAFTS. THE KILN RADAR SUGGESTS RAINFALL RATES MAY BE
IN THE 1 TO 2 INCH/HOUR RANGE WHICH SEEMS REASONABLE GIVEN THE
THERMODYNAMIC ENVIRONMENT THE STORMS RESIDE IN. THE FFG VALUES ARE
QUITE LOW STRETCHING ALONG THE CENTRAL APPALACHIANS AND BACK INTO
EASTERN OH. SUCH THRESHOLDS COULD BE EXCEEDED THROUGH 23Z.
UNFORTUNATELY THE CURRENT HIGH-RES MODELS HAVE DONE A POOR JOB
HANDLING THE ONGOING CONVECTION. HOWEVER...THE SIGNAL OF A HEAVY
RAINFALL EVENT IS INDICATED ACROSS THE BOARD WHICH RAISED
FORECASTER CONFIDENCE.  


RUBIN-OSTER

ATTN...WFO...CTP...PBZ...RLX...CLE...

ATTN...RFC...NCRFC...OHRFC...

LAT...LON   42008088 41958027 41807983 41447939 41047912 40377887
            39827902 39097969 38688051 38778135 39078179 40158192
            40988233 41678200 42008088