Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 191737
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
137 PM EDT Sat May 19 2018

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 330 AM EDT Sat May 19 2018

Low pressure over Indiana will continue to produce scattered
showers today as it moves slowly north. Another low pressure
system now over the Central Plains will follow on it`s heels and
bring more scattered showers Sunday and Monday. High pressure
builds in on Tuesday, ending the shower threat and providing a
stretch of dry weather through the end of next week.

&&

.SHORT TERM...(Today through Monday)
Issued at 330 AM EDT Sat May 19 2018

Highest coverage of rain today will be this morning as showers
continue to lift north ahead of the approaching upper low over srn
Indiana. This afternoon the mid level trough axis will be passing
through and the shower coverage will decrease from west to east.

Low level westerly flow developing off Lk MI in the wake of the
mid level trough leads to a period of decent sfc convergence
along and east of highway 131 for a time this afternoon. We could
see a band of convection developing along this convergence zone
before the sfc trough exits to the east around 6 PM. Models
indicate around 1000 j/kg of MUCAPE developing east/south of
roughly a BTL to LAN line, so will carry a chance of tstms for
this area this afternoon.

A dry period is anticipated tonight with brief shortwave ridging,
but more showers are possible on Sunday, especially south, as
vorticity maxima are shown already coming out of the the central
plains shortwave trough. The main wave takes it`s time moving
east and the threat of showers will continue Sunday night and
Monday. We could see an MCS rolling east along the instability
gradient just south of MI on Sunday night and Monday morning if a
low level jet manages to develop, so have included a thunder risk
south of I-96.

.LONG TERM...(Monday night through Friday)
Issued at 330 AM EDT Sat May 19 2018

Weak low pressure moving across southern Lower Michigan will be
responsible for scattered showers and isolated thunderstorms Monday
night. By Tuesday the low will move east of the cwa and high
pressure over southern Canada will drift over the state. That should
produce a couple of dry days before it too moves east.

As the high moves east Thursday night, south flow ahead of an upper
trough and sfc cold front will result in showers develop over the
Mississippi Valley Friday. That area of precipitation will move east
by Saturday and scattered showers and thunderstorms are in the
forecast for the beginning of the weekend.

Highs will be a couple degrees above normal through the period and
should be near 80 by the end of the week.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 131 PM EDT Sat May 19 2018

Abundant low level moisture will keep the potential for low clouds
and fog going for the forecast period. Ceilings and visibilities
could increase for a few hours this afternoon...but will likely go
back down tonight as temperatures lower.

The atmosphere was destabilizing at this time...mainly toward KLAN
and KJXN. A few thunderstorms could develop in that region before
heading east during the afternoon. Will need to monitor the risk
for a few showers/storms later tonight tracking in from WI/IL.
Currently the potential appears too low to put them in forecast
for now.

&&

.MARINE...
Issued at 330 AM EDT Sat May 19 2018

The could be a brief period of hazardous winds/waves near Big and
Little Sable points late tonight and Sunday morning due to
northerly flow. Otherwise winds and waves expected to remain below
advisory criteria. Also a chance of some fog over the lake today
and tonight.


&&

.HYDROLOGY...
Issued at 318 PM EDT Fri May 18 2018

River levels are high across southern Lower Michigan. The rivers in
central Lower Michigan are near to a little above normal. No river
flooding is ongoing. We are not expecting significant amounts of
rain, with less than an inch of rain expected through Monday for
most locations. This may lead to a slowdown or pause of the river
level falls.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...Small Craft Advisory from 10 PM this evening to noon EDT Sunday
     for LMZ848-849.

&&

$$

SYNOPSIS...Meade
SHORT TERM...Meade
LONG TERM...04
AVIATION...MJS
HYDROLOGY...63
MARINE...Meade



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