MESOSCALE PRECIPITATION DISCUSSION 0016
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1156 AM EST SUN FEB 11 2018

AREAS AFFECTED...I-95 CORRIDOR

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

VALID 111655Z - 112255Z

SUMMARY...NARROW BANDS OF RAIN AND THUNDERSTORMS SHOULD CONTINUE
TO DEVELOP IN A PLUME OF DEEP MOISTURE AND ALONG A SURFACE
FRONT...AND THEN TRACK NEAR THE I-95 URBAN CORRIDOR THIS
AFTERNOON. WITH SOILS SATURATED AND SOME FLOODING ISSUES ALREADY
REPORTED...RAINFALL RATES APPROACHING 1 IN/HR COULD PRODUCE
LOCALIZED FLASH FLOODING.

DISCUSSION...REGIONAL RADARS SHOWED SOME NARROW BANDS OF
CONVECTION BECOMING MORE ORGANIZED IN THE PAST SEVERAL
HOURS...ROUGHLY ALONG A SURFACE FRONT THAT APPROXIMATELY DENOTED
THE NORTHWESTERN PERIPHERY OF DEEPER MOISTURE (PW NEAR OR ABOVE
1.5 INCHES AND SFC DEWPOINTS NEAR 60 DEGREES). HI-RES MODELS HAVE
STRUGGLED TO GET A HANDLE ON THE CONVECTIVE EVOLUTION THIS
MORNING...BUT MOST SEEM TO AT LEAST HINT AT THE SAME IDEA OF A
NARROW CONVECTIVE BAND PRODUCING HEAVY RAINFALL NEAR THE I-95
URBAN CORRIDOR THIS AFTERNOON. THE LATEST RADAR TRENDS ALSO SHOWED
DIMINISHING REFLECTIVITY VALUES BEHIND THE INCIPIENT CONVECTIVE
BAND...SUGGESTING THAT WHILE MODERATE-HEAVY RAIN MAY BECOME LESS
WIDESPREAD THIS AFTERNOON...HEAVY RAIN SHOULD ALSO BECOME
INCREASINGLY FOCUSED ALONG THE QUASI-STATIONARY SURFACE FRONT.

THE CONVECTION AS OF 17Z STRETCHED ROUGHLY FROM JUST NORTHWEST OF
RICHMOND... TO ANNAPOLIS... TO NEAR TRENTON... AND THIS
ORIENTATION WAS ROUGHLY PARALLEL TO OBJECTIVELY ANALYZED MEAN
850-300MB FLOW. RAP ANALYSIS ALSO SHOWED SEVERAL HUNDRED J/KG OF
MUCAPE ENCOMPASSING MOST OF THE OUTLINED DISCUSSION AREA.
THEREFORE...AS CONVECTION BECOMES DEEPER AND BETTER
ESTABLISHED...THERE WILL BE SOME POTENTIAL FOR TRAINING OF HEAVIER
INSTANTANEOUS RAIN RATES ACROSS THE REGION.

SO FAR THIS MORNING...RAIN RATES HAVE GENERALLY REMAINED AROUND
0.5 IN/HR OR LESS...BUT SMALL AND NARROW CORRIDORS OF UP TO 1
IN/HR HAVE BEEN ESTIMATED BY DUAL POL RADAR AND MRMS AT TIMES
WHERE FAVORABLE ECHO TRAINING OCCURS. THE EXPECTATION IS THAT THIS
WILL CONTINUE...WITH THE POSSIBILITY OF SOME NARROW BANDS OF
6-HOUR ACCUMULATION INTO THE 1-2 INCH RANGE. GIVEN ONE HOUR FFG
VALUES ARE EXTREMELY LOW (GENERALLY AROUND OR LESS THAN 0.5
INCHES) IN THE D.C.-BALTIMORE AND PHILADELPHIA-NYC CORRIDORS...ANY
OF THESE TRAINING BANDS OF CONVECTION COULD POTENTIALLY PRODUCE
LOCALIZED FLASH FLOODING.

LAMERS

ATTN...WFO...AKQ...CTP...LWX...OKX...PHI...RNK...

ATTN...RFC...MARFC...NERFC...

LAT...LON   41427308 41167265 40547329 39747384 38897495
            38647574 38227632 37787677 37337760 37577858
            38247840 39377728 40287616 40797542 41187458
            41337393