108
AWUS01 KWNH 272351
FFGMPD
MIZ000-280530-

Mesoscale Precipitation Discussion 0867
NWS Weather Prediction Center College Park MD
750 PM EDT Mon Jul 27 2026

Areas affected...Northern & Eastern Lower Peninsula of Michigan...

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

Valid 272350Z - 280530Z

SUMMARY...Strong thunderstorms with ample moisture for 1.5-2"/hr
rates show signs of upstream strengthening for repeating/training
that may result in 2-3.5" totals and localized flash flooding
through early overnight period.

DISCUSSION...23z surface analysis depicts a subtle surface wave in
the center of the MI U.P, between P53 and ISQ  along a quickly
advancing cold front.  This is generally collocated with the left
exit region of strong 110-120kt 250mb jet crossing Lake Superior
and strengthening shortwave.  VWP and RAP analysis also denote
this inflection, perhaps enhanced by the shapes of the Lakes and
prior wave, to 850mb, but unlike the surface; the 850mb boundary
extends southeastward across the northern LP into the `Thumb` and
Ontario Peninsula.  In the wake of the initial shortwave, strong
southwesterly flow along/ahead of the cold front has strengthened
to 30-35kts and advected higher moisture and unstable air to
replenish/enhance unstable areas of the northern LP that were not
mixed over with the initial convection.

Surface Tds in the upper 60s, near 70F combined with pooled
moisture along the 850mb boundary is support 1500-2000 J/kg of
MLCAPE and total PWats starting to near 2.0".  The strong
isentropic ascent/convergence has resulted in stronger
thunderstorms in Alpena/Alcona county, with additional upstream
development through the northern Lake Michigan Islands.  Rates of
1.5-2"/hr are likely to become more common, but given inflection
of deepening, deep layer cyclone; the pooling of moisture and
favorable unidirectional steering flow should allow for expanding
development and potential for training thunderstorms over the next
few hours.  Recent HRRR solutions suggest, as evening turns to
night, strengthening LLJ and boundary layer decoupling may allow
for cells to become a bit more surface rooted.  This would
generally deflect the track of the training potential more south
of southeast which would bring areas surrounding Saginaw Bay into
the eastern Thumb of Michigan and perhaps even northern suburbs of
Detroit for training/repeating cells into the early overnight
period as well.

Naturally lower FFG values across the northeast tip of the LP into
the `Thumb` are about <2"/hr and 2-3"/3hrs; both of which are well
in the range of localized exceedance.  As such, flash flooding is
considered possible through 05z tonight.

Gallina

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

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

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

LAT...LON   45888546 45858497 45658411 45188329 44748292
            44108248 43088221 42568257 42488326 43128390
            44198450 44648503 45018547 45398580 45778576