MESOSCALE PRECIPITATION DISCUSSION 0402...CORRECTED
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
314 PM EDT WED JUL 04 2018

CORRECTED FOR TYPOS

AREAS AFFECTED...NORTHERN NE & VICINITY

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

VALID 041909Z - 050109Z

SUMMARY...ELEVATED CONVECTION APPEARS TO BE IN THE PROCESS OF
BECOMING MORE SURFACE-BASED AND INTENSIFYING.  HOURLY RAIN TOTALS
TO 2" WITH LOCAL AMOUNTS TO 4" ARE EXPECTED.

DISCUSSION...CONVECTION APPEARS TO BE INTENSIFYING AND TRYING TO
ALIGN AS OF LATE NEAR THE CENTRAL AND EASTERN NE/SD BORDER,
ELEVATED OVER A STATIONARY FRONT.  WATER VAPOR IMAGERY SHOWS A
SHORTWAVE MOVING ACROSS THE DAKOTAS WITH ANOTHER APPROACHING FROM
THE WEST-SOUTHWEST ACROSS NORTHWEST NE.  CIN IS ERODING ACROSS THE
REGION PER SPC MESOANALYSES AND CUMULI APPEAR TO BE FORMING CLOSER
TO THE FRONT SOUTH OF THE ONGOING CONVECTION CLOSER TO THE ML CAPE
GRADIENT.  PRECIPITABLE WATER VALUES OF 1.5-1.75" LURK ACROSS THE
AREA PER GPS VALUES AND RAP MASS FIELDS.  INFLOW AT 850 HPA IS
20-25 KNOTS FROM THE SOUTH TO SOUTHWEST PER VAD WIND PROFILES IS
IMPORTING 2000-4000 ML CAPE PER SPC MESOANALYSES.  EFFECTIVE BULK
SHEAR IN THE REGION IS 30-40 KTS.

THE 12Z HREF PROBABILITIES OF 1"+ OF RAIN IN AN HOUR HAVE BEEN
INSISTING THAT OVERNIGHT CONVECTION SHOULD HAVE FADED BY NOW AND
THAT NEW CONVECTION WOULD FLOURISH AFTER 21Z -- IT APPEARS TO BE A
FEW HOURS AHEAD OF SCHEDULE WHEN COMPARING ONGOING RADAR IMAGERY
TO THE MODEL FIELDS.  WHAT APPEARS MORE LIKELY IS THAT
SURFACE-BASED CONVECTION WOULD DEVELOP SHORTLY ACROSS NORTHERN NE
WHICH WOULD SPREAD EASTWARD ACROSS THE STATE WITH TIME, PERHAPS
CLIPPING SOUTHEASTERNMOST SD AND NORTHWEST IA IN THE PROCESS.  THE
MESOSCALE GUIDANCE GENERALLY AGREES ON LOCAL AMOUNTS IN THE 3"
RANGE, BUT THAT ASSUMES THAT CONVECTION IS NOT OCCURRING NOW. 
HOURLY RAIN TOTALS TO 2" WITH LOCAL AMOUNTS TO 4" SEEM MORE
REALISTIC.  THIS WOULD CHALLENGE FLASH FLOOD GUIDANCE, OUTSIDE OF
THE NE SANDHILLS.

ROTH

ATTN...WFO...FSD...GID...LBF...OAX...UNR...

ATTN...RFC...MBRFC...

LAT...LON   43249704 42939625 41919607 41599747 41569908
            41690067 42420039 43010007 43179946