618
AWUS01 KWNH 190241
FFGMPD
MIZ000-INZ000-WIZ000-ILZ000-190845-

Mesoscale Precipitation Discussion 0957
NWS Weather Prediction Center College Park MD
1040 PM EDT Mon Aug 18 2025

Areas affected...Southern WI...Northern half of IL...Northwest
IND...Far Southwest LP of MI...

Concerning...Heavy rainfall...Flash flooding likely

Valid 190245Z - 190845Z

SUMMARY...Incidents of flash flooding likely to continue, yet
overall coverage/totals will reduce with increasing forward speed.
 Best chance for flash flooding will be new `repeated` cell tracks
across S WI/NE IL

DISCUSSION...GOES-E WV, RADAR and RAP analysis show southern
stream, convectively enhanced shortwave/MCV feature is pressing
eastward across Chicago into southern Lake Michigan at this time,
continuing to drive strongest downstream low level convergence
along the quasi-bowing feature from northwest IND southward across
the Kankakee Valley.  Storms remain in unstable environment with
ample deep layer moisture (Tds in the mid 70s and total moisture
over 2"), but the stationary front remains anchored across
southwest LP of MI into north-central IND before Tds and unstable
air rapidly srop off, so there is a narrow area of enhanced
rainfall rates up to 2", but cells should quickly diminish into
the more stable air.  Additionally, area across LP of MI and
Northeast IND has been much drier and FFGs reflect that, further
reducing the risk to all but the most ideal training across
urban/low infiltration ground conditions.

However, the upstream flanking line across into central IL, does
remain very unstable with MUCAPEs of 2000-3000 j/kg and solid
moisture flux convergence along the confluent low level flow
regime.   Deep layer steering may allow for some southwest to
northeast repeating, though height-falls from the passing
shortwave/MCV should allow for southeast propagation to limit
overall totals to 2-3", lower FFG values of less than 2"/hr and
1.5-2.5"/3hrs in all but the further southwest portions of central
IL remain at good risk of locally being exceeded through the next
few hours.

Further north...S WI/N IL...
GOES-E WV depicts core of larger/synoptic to mesoscale shortwave
feature across central to S WI, is exiting and downward mixing is
starting to help advance the stationary front across SW WI through
depth, sharpening convergence along and south of the boundary.
While partially mixed, there remains ample remaining unstable air
of 1500-2000 J/kg and ample deep layer moisture to support an
additional round of stronger thunderstorms.  These upstream
thunderstorms will be narrower in nature but should have the
opportunity to track across areas already affected by heavy
rainfall with rates of 1.75-2"/hr; localized additional 1-3"
totals would reaggravate any flooding conditions across S WI and
few northern rows of N IL.  As such, localized incidents of flash
flooding are likely to persist through the overnight period.

Gallina

...Please see www.wpc.ncep.noaa.gov for graphic product...

ATTN...WFO...DVN...GRR...ILX...IND...IWX...LOT...MKX...

ATTN...RFC...MSR...TIR...NWC...

LAT...LON   43398673 43118619 42518584 41708587 40518639
            39988741 39908888 40019006 40469037 40869000
            41278958 41708930 42168939 42489001 42988980
            43348839