Graphic for MPD #0816

MESOSCALE PRECIPITATION DISCUSSION 0816...CORRECTION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
940 PM EDT WED SEP 20 2017

CORRECTED FOR GRAMMAR FLAWS IN THE DISCUSSION SECTION

AREAS AFFECTED...EASTERN IA, NORTHWEST IL, & NORTHEAST MO

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

VALID 210133Z - 210733Z

SUMMARY...THUNDERSTORM BANDS ARE DEVELOPING AHEAD OF A STALLING
FRONT.  HOURLY RAIN TOTALS TO 2.5" WITH LOCAL AMOUNTS TO 4" ARE
POSSIBLE.

DISCUSSION...NON-OPERATIONAL GOES-16 SATELLITE AND RADAR IMAGERY
SHOW THE DEVELOPMENT OF THUNDERSTORMS ACROSS EASTERN IA, NORTHEAST
MO, AND NORTHWEST IL.  RECENT RAP ANALYSES/FORECASTS INDICATE THAT
TEMPERATURES AT 700 HPA ARE NEAR 9C, WHICH LATELY HAS ACTED AS THE
EDGE OF THE EFFECTIVE CAPPING INVERSION.  PRECIPITABLE WATER
VALUES ARE ~1.75" PER GPS DATA AND THE 00Z SOUNDING FROM
DVN/DAVENPORT IA.  DIVERGENCE ALOFT IS BEING AIDED BY A SHORTWAVE
MOVING THROUGH NORTHERN MN AND AN UPPER LOW DROPPING THROUGH THE
CENTRAL APPALACHIANS PER WATER VAPOR IMAGERY.  INFLOW AT 850/700
HPA IS CONVERGENT AT ~25 KTS PER VAD WIND PROFILES AND RECENT RAP
FORECASTS.  EFFECTIVE BULK SHEAR IN THE REGION IS 25-30 KTS PER
RECENT SPC MESOANALYSES, WHICH ALONG WITH FAIRLY UNIDIRECTIONAL
FLOW WITH HEIGHT HAS LED TO THE DEVELOPMENT OF A COUPLE LINEAR
BANDS OF THUNDERSTORMS FORMING ALONG A PRE-FRONTAL TROUGH.  MU
CAPE VALUES ARE ~3000 J/KG.

THE GUIDANCE HAS A SIGNAL FOR HEAVY RAINFALL IN THIS REGION, BUT
ONLY IN THE 2-3" RANGE.  THE GUIDANCE FARTHER NORTHEAST ACROSS WI
WAS SOMEWHAT UNDERSELLING THE POTENTIAL, WHICH APPEARS GREATER IN
THIS REGION.  GALVEZ-DAVISON INDICES BASED ON THE 18Z GFS SHOW
INCREASING VALUES THROUGH 06Z, WHICH IMPLIES GREATER THUNDERSTORM
COVERAGE WITH TIME.  THE LOW-LEVEL INFLOW IS EXPECTED TO REMAIN
ESSENTIALLY STATIONARY INTO THIS REGION AHEAD OF A STALLING FRONT
AND THAT THE BANDS WON'T BE MOVING PARTICULARLY FAST WITH TIME. 
DEVELOPING CIN COULD ALLOW THE ACTIVITY TO HOLD UP FOR AN HOUR OR
TWO BEFORE MOVEMENT CAN BEGIN.  FORWARD PROPAGATING CONVECTIVE
VECTORS IMPLY EAST MOVEMENT AT 10-15 KTS IS POSSIBLE, WHICH COULD
LAY DOWN AN EAST-WEST OUTFLOW BOUNDARY AT THE LEADING EDGE OF A
FORMING COLD POOL ACROSS NORTHERN MO, WHICH COULD INCREASE
PRECIPITATION RATES/AMOUNTS DOWN SOUTH WITH TIME.  HOURLY RAIN
TOTALS TO 2.5" WITH LOCAL AMOUNTS TO 4" APPEAR POSSIBLE.

ROTH

ATTN...WFO...DMX...DVN...EAX...ILX...LOT...LSX...MKX...

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

LAT...LON   42539014 41948910 39989096 39399418 40959226
           


Last Updated: 940 PM EDT WED SEP 20 2017