Flash Flood Guidance
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AWUS01 KWNH 230413

Mesoscale Precipitation Discussion 0828
NWS Weather Prediction Center College Park MD
1211 AM EDT Fri Oct 23 2020

Areas affected...central and southern WI into northern Lower MI

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

Valid 230408Z - 230910Z

Summary...Training of showers and thunderstorms will likely
continue For another few hours from WI into Lower MI. Rainfall
intensity should wane through the night but an additional 1 to 2.5
inches will be possible through 10Z with localized flash flooding.

Discussion...Regional radar imagery at 0330Z showed a SW to NE
axis of showers and thunderstorms extending from northeastern IA
into south-central WI and northern Lower MI. Observed rainfall
rates within this axis have been as high as 1.6 in/hr over
southwestern WI (ending 02Z) where MUCAPE was estimated to be
between 500 and 1000 J/kg. Low level convergence near 850 mb has
been focusing the axis of heavy rain with southwesterly winds
peaking between 50 and 60 kt and mean steering flow parallel to
the low level convergence axis. In addition, the region sits
within the entrance region of a 150 kt jet located at 250 mb just
north of the region which is aiding ascent.

As two surface lows located along a frontal system through the
Upper Midwest advance toward the northeast in the short term, slow
eastward translation of the low level convergence axis will occur,
with peak rainfall rates of 1 to 1.5 in/hr impacting locations
from central and eastern WI into northwestern Lower Michigan. Some
of these locations have picked up at least 1 to 2 inches of rain
over the past 12 hours and areas of flash flood guidance are as
low as 1 to 1.5 inches in 3 hours. However, a large mitigating
factor toward additional flash flooding will be decreasing MUCAPE
throughout the remainder of the night as the instability axis
advances south and east of the region through 10Z. Therefore, only
localized flash flooding is expected over the next 2-4 hours, with
the threat waning through 10Z.


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



LAT...LON   45618462 45578366 44898354 44188496 43868587
            43468705 43358754 42798979 43209047 44138885
            44668759 45318583

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