MESOSCALE PRECIPITATION DISCUSSION 0134
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1102 PM EDT FRI MAY 11 2018

AREAS AFFECTED...SOUTHERN LOWER MI

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

VALID 120301Z - 120801Z

SUMMARY...SHOWERS AND THUNDERSTORMS ARE ON THE INCREASE ACROSS
SOUTHERN LOWER MI.  HOURLY RAIN TOTALS TO 1.5" WITH LOCAL AMOUNTS
TO 3" ARE POSSIBLE THROUGH 08Z.

DISCUSSION...A SHORTWAVE MOVING ACROSS LAKE MI INTO SOUTHWEST MI
ALONG WITH ANOTHER SHORTWAVE FARTHER NORTHWEST ACROSS WI HAVE
FOSTERED A RECENT UPTICK OF SHOWER AND THUNDERSTORM ACTIVITY
ACROSS THE LOWER PENINSULA OF MI NEAR THE 850 HPA SLICE OF A
STATIONARY FRONT.  THE 00Z SOUNDING OUT OF DETROIT IS MOIST, WITH
WET BULB ZERO HEIGHTS JUST OVER 9,000 FEET.  UPSTREAM MU CAPE
VALUES OF 500-1000 J/KG IS SHIFTING SLIGHTLY NORTHWARD.  INFLOW AT
850 HPA IS WEST-SOUTHWEST AT 20 KTS PER THE GRAND RAPIDS VAD WIND
PROFILE, WITH SPC MESOANALYSES ADVERTISING 35-50 KTS OF EFFECTIVE
BULK SHEAR.  GPS DATA AND NEARBY SOUNDINGS SHOW PRECIPITABLE WATER
VALUES IN THE 1.1-1.25" RANGE.

INFLOW AT 850 HPA IS EXPECTED TO INCREASE TO 40-45 KTS AND VEER
SOMEWHAT OVERNIGHT AS THE SHORTWAVES PASS BY, WHICH SHOULD ALLOW
CONVECTION TO MOVE FROM WEST TO EAST.  CELL TRAINING APPEARS TO BE
THE MAIN HEAVY RAIN THREAT, THOUGH THE DEVELOPMENT OF A RANDOM
MESOCYCLONE CAN'T BE RULED OUT.  THE MESOSCALE GUIDANCE IS
GENERALLY AGREEABLE ON THE CONVECTIVE RAMP UP OVERNIGHT, WITH A
40%+ CHANCE OF 1" AN HOUR AMOUNTS INDICATED IN THE 04-06Z TIME
FRAME, WITH FADING AMOUNTS THEREAFTER AND AN ENDING THREAT BY 08Z.
 GIVEN THE AVAILABLE MOISTURE AND INSTABILITY, HOURLY RAIN TOTALS
TO 1.5" ARE SUPPORTED, WITH THE MESOSCALE GUIDANCE INDICATED LOCAL
AMOUNTS TO 3", WHICH SEEMS REASONABLE AND WOULD SLIGHTLY EXCEED
FLASH FLOOD GUIDANCE VALUES. 

ROTH

ATTN...WFO...DTX...GRR...IWX...

ATTN...RFC...NCRFC...OHRFC...

LAT...LON   42758371 42668252 42218303 41798345 41778510
            41818709 42368718 42738685