Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 121006
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
606 AM EDT Sun Jul 12 2020

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 330 AM EDT Sun Jul 12 2020

-Dry through Tuesday

-Next chance of active weather Wednesday, Wednesday Night

-Hot and humid next weekend; possibly stormy too

&&

.DISCUSSION...(Today through next Saturday)
Issued at 330 AM EDT Sun Jul 12 2020

-- Dry through Tuesday --

Other than the risk for a few isolated showers or storms this
morning south of I-96 related to the shortwave passing by to our
south, the next few days will be dry with comfortable humidity
levels. We have a dry air mass with PWATs under an inch and
surface ridging building in from the northwest.

After pleasant high temps around 80 today and Monday, it does
turn a bit warmer by Tuesday with highs in the mid to upr 80s as
the sfc ridge begins to slip away and a low level southerly flow
develops.

-- Next chance of active weather Wednesday, Wednesday night --

A sfc frontal boundary leans into the area from the northwest on
Wednesday then stalls overhead as a shortwave approaches from the
southwest late in the day. Deep layer shear of 30-40 kts is
progged by the ECMWF and GFS Wednesday evening, lending support
for a round of strong to svr storms, but it`s way too early to
speculate on how much instability may be present.

This mid-week event actually has more the look of a potential
heavy rain event Wednesday night - with PWATs near 2 inches, a
stalled frontal boundary, and right entrance region upr jet
dynamics in play.

-- Hot and humid next weekend; possibly stormy too --

The sfc frontal boundary appears to slip just south of MI for
Thursday into Friday but then swings back north trough the area
as a warm front Friday night. ECMWF is showing H8 temps around
23C on Saturday into Sunday along with sfc dew pts around 70.

This would suggest highs in the low to mid 90s Saturday with heat
indices near or exceeding 100. It would also likely mean that
moderate to extreme instabilty will be present with capes in
excess of 3500 J/KG.

While MCS activity next weekend should initially tend to favor
the warm front and higher shear situated off to our north over nrn
MN/WI and upr MI, it could also easily propagate southward into
our high instability air mass. Currently that appears most
possible on Sat ngt into Sunday.

&&

.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
Issued at 601 AM EDT Sun Jul 12 2020

Ongoing convection over Lake Michigan is associate with a short
wave clipping southern Lake Michigan and will dissipate and move
south with time and should remain west of Kalamazoo.

Otherwise, VFR conditions are expected through the period.

&&

.MARINE...
Issued at 330 AM EDT Sun Jul 12 2020

Still on track for a strong northerly flow event this afternoon
and early evening as the passing mid level shortwave pulls down
another sfc cold front. No changes to the current marine headlines
are needed, which highlight the threats to both small craft and
beach goers.

Cold advection pouring south over the warm lake waters in
the 70s will indeed kick up the waves, especially south of Grand
Haven where wave heights will peak at 6-7 feet early this evening.
The north side of north piers will be the worst place to swim due
to strong structural currents. Holland State Park is one example
of a highly dangerous place to swim today.


&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Beach Hazards Statement from noon EDT today through late tonight
     for MIZ050-056-064-071.

     Beach Hazards Statement through this evening for MIZ037-043.

LM...Small Craft Advisory until midnight EDT tonight for LMZ848-849.

     Small Craft Advisory from noon today to 4 AM EDT Monday for
     LMZ844>847.

&&

$$

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



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