MESOSCALE PRECIPITATION DISCUSSION 0473
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
341 PM EDT WED JUL 12 2017

AREAS AFFECTED...EASTERN NE & PORTIONS OF IA

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

VALID 121939Z - 130139Z

SUMMARY...THUNDERSTORMS ARE EXPANDING IN COVERAGE NEAR AND
DOWNWIND OF A MESOSCALE WAVE.  HOURLY RAIN RATES TO 2" WITH LOCAL
AMOUNTS TO 4" ARE POSSIBLE.

DISCUSSION...THUNDERSTORMS HAVE BEEN BLOSSOMING TO THE EAST OF AN
MCV ACROSS EASTERN NE AND HAVE TAKEN ON A TRAINING SIGNATURE. 
INFLOW AT 850 HPA IS CONVERGENT AT 15-20 KTS (NEAR THE MAGNITUDE
OF THE MEAN 850-400 HPA WIND) WHICH IS IMPORTING THE HIGHER MLCAPE
VALUES FROM BEHIND THE WAVE WITHIN THE NORTHWEST FLOW.  MLCAPE
VALUES ARE 2000-4000 J/KG.  EFFECTIVE BULK SHEAR IS ~30 KTS, WHICH
HAS HELPED ORGANIZE THE TRAINING BAND.  PRECIPITABLE WATER VALUES
ARE 1.75-2". 

THE MESOSCALE GUIDANCE HAS A SIGNAL FOR RAIN HERE, BUT GENERALLY
APPEARS UNDERDONE - THE 16-17Z HRRR EXPERIMENTAL RUNS AND THE 12Z
CANADIAN APPEAR TO HAVE THE BEST HANDLE OF THIS ACTIVITY.  WITHIN
THE NEXT COUPLE HOURS, CIN SHOULD ERODE WHICH SHOULD ENHANCE
SURFACE-BASED CONVECTIVE ACTIVITY.  FORWARD PROPAGATION GENERALLY
TO THE EAST AT 20-25 KTS IS EXPECTED.  WITHIN SHORT TRAINING
BANDS, HOURLY RAIN RATES UP TO 2" AND LOCAL AMOUNTS UP TO 4" ARE
POSSIBLE OVER THE NEXT SEVERAL HOURS.

ROTH

ATTN...WFO...ARX...DMX...DVN...GID...OAX...

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

LAT...LON   42769123 41749153 41009371 40799613 41259774
            41999585