Mesoscale Precipitation Discussion 0725
NWS Weather Prediction Center College Park MD
119 AM EDT Tue Aug 28 2018

Areas affected...Northern Michigan

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

Valid 280518Z - 280818Z

Summary...A line of heavy thunderstorms in advance of low pressure
over northern Lake Michigan will cross the Straits of Mackinac and
eastern portions of the Upper Peninsula early this morning.

Discussion...KAPX radar is depicting one hour rain rates of 2 to
2.5 inches/hour across northern sections of Lake Michigan (near
Beaver Island) in a band on the northern extension of a bowing
squall. This segment of the line was oriented more east-west, but
is tilting north-south with the rest of the left side of the
bowing segment.

A swath of 2.25 inch precipitable water is across Lake Michigan on
the head of a 55 kt southwesterly low level jet with 1500 MLCAPE
per RAP analysis (and VWP for the jet). The tilting of this
northern segment more north-south is orienting it in line with the
low level flow as well as the deep layer mean wind. Therefore,
this heavy rain should persist over the next hour or two as it
pushes across the eastern Upper Peninsula and extreme northern
Lower Peninsula.

The area has generally received near normal rainfall over the past
week. Flash flood guidance is generally 1.5 to 2 inches per hour,
so rain rates exceeding this makes flash flooding possible.

Areas immediately farther south will have the bowing segment cross
with less time in the heavy rain.

Jackson

ATTN...WFO...APX...MQT...

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

LAT...LON   46778480 46538412 45968378 45488397 45428517
            45558613 46578670