Graphic for MPD #0911

MESOSCALE PRECIPITATION DISCUSSION 0911...CORRECTED
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
451 PM EDT TUE OCT 24 2017

CORRECTED FOR TYPO IN THE FIRST DISCUSSION PARAGRAPH

AREAS AFFECTED...SOUTHEAST NY & SOUTHWEST NEW ENGLAND

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

VALID 241954Z - 250154Z

SUMMARY...A STALLING SURFACE BOUNDARY COMBINED WITH AMPLE MOISTURE
AND SUFFICIENT INSTABILITY IS EXPECTED TO LEAD TO HOURLY RAIN
TOTALS UP TO 1.75" AND LOCAL AMOUNTS TO 4".

DISCUSSION...SATELLITE AND RADAR IMAGERY SHOW A STALLING POLAR
FRONT ACROSS THE EASTERN SHORE, NJ, AND SOUTHEAST NY AT THE
PRESENT TIME.  RECENT RADAR IMAGERY SHOWS THE BEGINNING OF
OCCASIONAL CELL TRAINING EAST OF KINGSTON AND POUGHKEEPSIE NY. 
HOURLY RAIN TOTALS HAVE APPROACHED 1.4" WITHIN THE SHORT TRAINING
BAND HERE BEFORE IT EDGED EASTWARD.  THE REGION IS NEAR THE BASE
OF A SHORTWAVE MOVING ACROSS FAR SOUTHEAST ONTARIO AND AHEAD OF A
SECOND SHORTWAVE MOVING INTO WV.  PRECIPITABLE WATER VALUES OF
1.4-1.75" EXIST IN THIS AREA PER RECENT GPS DATA.  INFLOW AT 850
HPA IS SOMEWHAT CONVERGENT OUT OF THE SOUTH TO SOUTH-SOUTHWEST AT
40-50 KTS PER VAD WIND PROFILES.  EFFECTIVE BULK SHEAR IS 30-50
KTS PER THE MOST RECENT SPC MESOANALYSIS.  ML CAPE VALUES ARE >
500 J/KG WITHIN THIS SATURATED AIRMASS.

THE 18Z HRRR/16Z HRRR EXPERIMENTAL APPEAR TO HAVE SOME GRASP OF
WHAT IS ONGOING.  THEY, ALONG WITH THE 12Z GFS-BASED
GALVEZ-DAVISON INDEX FORECAST, SHOW/IMPLY AN INCREASE IN
CONVECTIVE COVERGE WITHIN THIS NEARLY STALLED BAND UNTIL ~02Z
BEFORE FADING THEREAFTER AS MU CAPE WEAKENS AND FORWARD
PROGRESSION ATTEMPTS TO RESUME (SHOWN IN RAP-BASED BOUNDARY LAYER
CONVERGENCE FIELDS) AS THE UPSTREAM UPPER TROUGH STRENGTHENS AND
EDGES EASTWARD.  HOURLY RAIN TOTALS TO 1.75" ARE EXPECTED.  THE
MESOSCALE GUIDANCE HAS A MODEST SIGNAL FOR 3-4" OF RAIN THROUGH
02Z.  THIS WOULD BE PROBLEMATIC WITHIN HILLY TERRAIN AND URBAN
ENVIRONMENTS.

ROTH

ATTN...WFO...ALY...BOX...BTV...GYX...OKX...

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

LAT...LON   43377309 43327222 41037232 40657291 40587407
            41737395 42487376


Last Updated: 451 PM EDT TUE OCT 24 2017