Special Marine Warning 3, NWS Grand Rapids, MI

Area Forecast Discussion
National Weather Service Grand Rapids MI
330 AM EDT Fri Jun 18 2021

LATEST UPDATE...
Synopsis/Discussion/Marine

.SYNOPSIS...
Issued at 330 AM EDT Fri Jun 18 2021

-Thunderstorms, with a risk of gusty winds early this morning

-Occasional rounds of convection Saturday through early Monday

-Warm through the weekend; sharp cool down early next week

&&

.DISCUSSION...(Today through next Thursday)
Issued at 330 AM EDT Fri Jun 18 2021

-Thunderstorms, with a risk of gusty winds early this morning

We'll be watching the line segments moving east from southern
Wisconsin early this morning. The first one north of MKE
extrapolates to the lake Michigan shoreline near MKG around 5 am
and continuing ESE from there through the early morning hours.
These segments are not too impressive but a swath/corridor of
gusty winds to 40 mph may affect the area from I-96 south early
this morning.

Once the early morning storms exit, some potential exists for new
storms, possibly strong or severe, to fire south and east of GRR
by afternoon. SB Capes in excess of 3000 j/KG are shown to develop
as dew pts near 70 push in from the southwest. Sfc convergence is
decent through around 4 pm before the low level flow becomes more
westerly with the cold frontal passage.

So the period from about Noon to 4 pm will need closely monitored
around JXN, after which time the main svr wx risk will shift
south of MI where SPC has an enhanced risk.

-Occasional convection Saturday through early Monday

Fast west-northwest flow aloft remains over the Grtlks Rgn through
the weekend. Models are in good agreement on the next shortwave in
this pattern dropping through Lwr MI on Saturday, possibly
triggering another round of convection. There are some slight timing
differences but this feature looks to arrive already by mid morning
after some sfc heating/instability has had a chance to develop.

Instability Saturday will be lower than today since dew points
will be a bit lower behind today's fropa, but capes around 1500
J/kg and deep layer shear over 35 kts will still be sufficient to
support the possibility of some stronger storms especially east
of Hwy 131.

After a brief period of quieter weather Saturday night into early
Sunday, a digging nrn stream trough over the Northern Plains
induces a decent low level jet from MO to srn MI by 00Z Monday.
Expect convection to develop on the nose of this low level jet and
returning warm front later Sunday, with some stronger storms and
locally heavy rainfall possible.

Could be an active period in west Michigan Sunday evening as
upstream trough continues to dig/deepen and cold front approaches
from the west. Convective threat looks to finally end early
Monday with the passage of that strong sfc cold front.

-Warm through the weekend; cool down early next week

Guidance continues to support highs of 85 to 90 through Sunday
although humidity not too high with dew points generally around 60
after today's frontal passage. Deep upper trough arrives overhead
by Tuesday behind the Monday's strong cold front, resulting in
chilly highs only in the 60s. That cold air doesn't stick around
long however with temps rebounding back near normal for mid week.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 146 AM EDT Fri Jun 18 2021

Showers and thunderstorms will move over the terminals from
Wisconsin within the next few hours. Expect convection to persist
at the eastern TAF sites through 13z or so. IFR vsbys are
anticipated in storms.

Conditions will improve as the morning progresses with VFR
returning by the afternoon.

&&

.MARINE...
Issued at 330 AM EDT Fri Jun 18 2021

Expect occasional gusty winds and briefly higher seas over Lk MI
early this morning as scattered tstms and the low level jet move
through. Otherwise winds and waves remaining below advisory
criteria through the weekend. We could be looking a somewhat lengthy
period of rough conditions on the lake from Sunday night through
Tuesday as a stronger weather system moves through and cold air
pours in behind it.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...None.
&&

SYNOPSIS...Meade
DISCUSSION...Meade
AVIATION...04
MARINE...Meade

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