AWUS01 KWNH 221348
FFGMPD
MIZ000-221930-

Mesoscale Precipitation Discussion 1110
NWS Weather Prediction Center College Park MD
947 AM EDT Sat Aug 22 2026

Areas affected...Lower Peninsula of Michigan...

Concerning...Heavy rainfall...Flash flooding possible

Valid 221350Z - 221930Z

SUMMARY...Multiple rounds of thunderstorms capable of 1.5"/hr with
localized slow motions further north and back-building/repeating
further south may allow for localized flash flooding concerns
through early afternoon.

DISCUSSION...GOES-E WV shows a broad longwave trof centered over
the LP of MI this morning with a stronger upstream shortwave
digging out of WI providing height-falls and
strengthening/sharpening of the surface low near the Mackinaw
Strait with an attendant cold front angling southwest just
crossing the far southeast side of Lake Michigan into SW MI at
this time.  A upstream exiting MCV between Lake Erie and Ontario
allows for broadening downstream portion of the longwave trough
with solid diffluence aloft to promote ascent along and well ahead
of the cold front.   Instability has been a limiting factor
through eastern MI but RAP analysis modified by recent surface
temperatures suggests weakly capped 1000-1500 J/kg of MLCAPE
reducing to 250 J/kg in far E MI, with initial, early morning
convection exhausting much of it.  However, that convection helped
develop a WSW to ENE boundary and with favorable southerly
component to low level winds and available unstable air has been
able to develop stronger flanking development with somewhat
favorable orientation to the deep layer mean flow to increase residency.

Surface Tds in the low 60s and modest mid-level moisture with the
effective warm conveyor pressed eastward is limiting overall
available moisture to around 1.25"; so localized convergence/flux
will be the driving force for rates of 1.5" with occasionally
higher localized peaks. This is falling generally over the core of
the sandier soils of central LP where FFGs are high, but proximity
to urban locations along the I-96 corridor may still pose urban
flash flooding, but at least prep the area for later developing
convection from the cold front toward early afternoon.

Further north, as the shortwave sharpens the mean steering flow
will reduce in the trough especially along/east of the
strengthening surface wave. So cells will increase in residency
toward NE LP.  This is also where FFGs are naturally a bit lower
with spots of 1-1.5"/hr and 1.5-2.5"/3hrs.   As such, with
multiple rounds and possible mergers due to the sharpening/pivot
in the line, localized totals of 2-3" are possible and may result
in localized flash flooding concerns toward afternoon.

Gallina

ATTN...WFO...APX...DTX...GRR...

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

LAT...LON   45408442 45358357 44998319 44348316 44148285 
            43718246 42678240 42378281 42188307 42148364 
            42158500 42578530 43298490 43808493 44228553 
            45058512 

$$
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