MESOSCALE PRECIPITATION DISCUSSION 0017
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
432 PM EST THU FEB 15 2018

AREAS AFFECTED...CTRL/ERN OH...PANHANDLE OF WV...SWRN/SCTRL PA

CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE

VALID 152130Z - 160330Z

SUMMARY...HEAVY RAIN BANDS APPEAR LIKELY TO DEVELOP BY 6 PM EST
AND THEN TRAIN IN A WEST-TO-EAST FASHION ALONG THE I-70 CORRIDOR
THIS EVENING. HOURLY RAIN RATES APPROACHING 1 IN/HR EMBEDDED
WITHIN STEADY RAIN THROUGH THE EVENING MAY PRODUCE AREAS OF
LOCALIZED FLASH FLOODING.

DISCUSSION...THE LATEST SURFACE OBSERVATIONS AND RAP OBJECTIVE
ANALYSIS DEPICTED BROAD...MOIST...SOUTHWESTERLY LOW-LEVEL INFLOW
ACROSS THE OHIO VALLEY REGION. THE CINCINNATI (KCVG) ASOS RECORDED
A DEWPOINT OF 64 DEGREES AT 20Z...WHICH HAS NOT BEEN PREVIOUSLY
REPORTED ON AN HOURLY OBSERVATION IN FEBRUARY (PERIOD OF RECORD
1947-PRESENT). THIS IS AN ISOLATED EXAMPLE...BUT IS INDICATIVE OF
ANOMALOUSLY HIGH LOW-LEVEL MOISTURE VALUES FOR FEBRUARY ACROSS THE
REGION. AS THE BOUNDARY LAYER FLOW REACHES THE SURFACE WARM
FRONT...IT WAS BECOMING INCREASINGLY VEERED TO A WESTERLY
DIRECTION. AND THROUGH THE DEPTH OF THE TROPOSPHERE...STREAMLINES
WERE GENERALLY CONVERGING INTO DEEP WESTERLY FLOW. THIS WOULD
FAVOR TRAINING RAIN BANDS...AS WOULD THE ORIENTATION OF THE
LOW-LEVEL INFLOW (FROM THE WSW FAVORING BACKBUILDING).

REGIONAL RADARS WERE SHOWING AN INCREASE IN REFLECTIVITY BETWEEN
20Z AND 2130Z JUST NORTH OF THE I-70 CORRIDOR...AND SEVERAL
LIGHTNING STRIKES HAD ALSO BEEN RECENTLY OBSERVED TO THE NORTHEAST
OF DAYTON OH. HI-RES MODELS ARE IN GOOD AGREEMENT THAT THIS
WEST-TO-EAST ORIENTED BAND OF HEAVIER RAIN WITH EMBEDDED
THUNDERSTORMS SHOULD CONTINUE TO ORGANIZE OVER THE NEXT COUPLE
HOURS AND TRAIN NEAR I-70 INTO THE EVENING HOURS. RECENT RUNS OF
THE HRRR AND NAM NEST BOTH SHOW THE POTENTIAL FOR HOURLY RAIN
RATES TO APPROACH OR EVEN EXCEED 1 IN/HR IN NARROW AND LOCALIZED
SWATHS DURING THE EVENING HOURS. NEARLY ALL HI-RES MODELS SHOW
LOCALIZED 6-HOUR RAINFALL MAXIMA ON THE ORDER OF 2-3 INCHES BY
03Z. THESE AMOUNTS MAY BE SUFFICIENT TO PRODUCE FLASH
FLOODING...PARTICULARLY IN URBANIZED AREAS OR SMALLER BASINS
EMBEDDED WITHIN SHARPER TERRAIN GRADIENTS.

THE AREA AROUND PITTSBURGH IN SOUTHWEST PENNSYLVANIA AND THE WEST
VIRGINIA PANHANDLE HAS SOME OF THE LOWEST FFG IN THE OUTLINED
AREA...AND THE 60-DAY PRECIPITATION ANOMALIES ARE HIGHEST IN THE
SAME AREA (NEAR OR IN EXCESS OF 150 PERCENT OF NORMAL). HI-RES
MODELS SHOW A CONSIDERABLE OVERLAP OF THE HEAVIER RAINFALL OVER
THE NEXT SIX HOURS...AND THEREFORE THIS IS A REGION THAT MAY BE
MORE HYDROLOGICALLY FAVORED FOR FLASH FLOODING.

LAMERS

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

ATTN...RFC...MARFC...OHRFC...

LAT...LON   41068009 40927835 40527752 40097767 39817856
            39808008 39798283 40078373 40738329 41028172