818
FXUS63 KGRR 300126
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
926 PM EDT Sat Jun 29 2024

.KEY MESSAGES...

- Slight chance of storms this evening, then cool and breezy
  Sunday

- Moderating Temperature Trend Next Week

- Chance for Thunderstorms Late Tuesday into Wednesday

&&

.UPDATE...
Issued at 926 PM EDT Sat Jun 29 2024

No changes planned to the current forecast. We are seeing
thunderstorms moving eastward across northeastern Lower MI at
this time ahead of a pronounced upper PV max crossing the Upper
Peninsula per water vapor satellite imagery. We also have showers
crossing central Lower MI a little farther to the south and this
includes our northeastern forecast area. But, forcing is less
pronounced even this slight distance south of the thunderstorms.
The central Lower MI activity also is quickly exiting to the
east. Hence, we are looking at only a very narrow window of
opportunity for thunderstorms in the Clare/Mount Pleasant area.

Farther south, a surface boundary is pressing southeast towards
the southern Lower MI state line. There could be a brief window
for a shower just east of Jackson given a northward moving outflow
boundary that may constructively interfere with the southeastward
moving boundary. Again though, we are looking at a very narrow
window of opportunity for what would be a low probability, low
impact scenario at this point anyway.

&&

.DISCUSSION...
Issued at 332 PM EDT Sat Jun 29 2024

- Slight chance of storms this evening, then cool and breezy
  Sunday

There are two chances we`re watching for development of storms in
our area for the rest of today. The first is in the far
south/southeast counties, where substantial instability and
moisture (dewpoints in the mid 70s) continue. There`s enough shear
in the column to potentially maintain some organization if
anything gets going, but the missing ingredient in this area is a
trigger/forcing mechanism. A weak shortwave moving across southern
Lake Michigan earlier tried to initiate some convection, but
things never really took off. As the evening progresses, we`ll be
watching what happens as the surface cold front sags into our area
around 00z from the northwest. It looks like the best chances for
storms will remain south of the Michigan/Indiana border (where
lift, moisture, and instability all overlap better), but can`t
rule out a stray storm trying to clip our southern areas.

Meanwhile, better atmospheric lift will also exist in Northern
Lower Michigan this evening associated with impressive 500 mb
CVA associated with the upper trough, which will move into Lower
Michigan around the same time as the surface cold front. Some
discrete convection and possibly a few strong to severe storms
could develop, but the best lift stays north of our area, so again
we`re thinking that we`ll be on the edge of the threat area. All
of this adds up to a situation where we`ll be watching closely for
severe risks this evening, but the most likely scenario is that
any severe storms stay just to the north and south of our area.

By midnight, the cold front will have come through the area, and
we`ll fall under the influence of northwest winds and cooler (and
drier) air moving in. These clearing skies and gusty winds will
continue all the way through Sunday, with a dangerous swimming day
along all Lake Michigan beaches expected for the day Sunday. See
the Marine section below for more info.

- Moderating Temperature Trend Next Week

It will be seasonably cool Monday with high pressure and northeast
winds which will keep high temps in the 70s. A southerly flow waa
pattern will develop on the back side of the departing ridge
beginning Tuesday. Max temps will reach the upper 70s to lower 80s
Tuesday and well into the 80s to near 90 degrees by Wednesday.

- Chance for Thunderstorms Late Tuesday into Wednesday

As a warmer and more humid airmass advects into our area there will
be a chance for a few showers and thunderstorms Tuesday into
Wednesday. However the greater risk for convection and severe
wx should stay off to our west across Iowa and southern Wisconsin
Tuesday where stronger instability is forecast to develop along
with forcing from the cold front.

The boundary will bring a chance of showers and storms into
Wednesday. However the boundary should tend to stall and wash
out with not much of an airmass change at all for our area mid to
late week. So while there is a relatively low risk for a shower or
storm Tuesday and Wednesday we expect that dry and increasingly
warmer and more humid conditions will prevail the majority of the
time. The focus for convection should be south of our area Thursday
and then a system approaching from the west will bring another
chance for showers and storms Friday.

&&

.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 740 PM EDT Sat Jun 29 2024

Cigs have scattered out across the region this evening. A cold
front is moving across Lake MI attm and will move across the
terminals tonight which will help to lower dewpoints.

There`s a fairly strong signal that we`ll see some MVFR ceilings develop
after midnight and dissipate prior to noon Sunday as subsidence
takes hold. Scattered VFR cu expected during the last portion of
the TAF period.

&&

.MARINE...
Issued at 332 PM EDT Sat Jun 29 2024

A small craft advisory and associated Beach Hazards statement has
been issued for all of our marine areas starting this evening and
continue through late Sunday evening. As winds shift around to the
northwest (and eventually north), waves will build into the 4 to
6 foot range as wind gusts in excess of 25 knots are possible in
all areas. The worst conditions are still expected Sunday morning,
but winds and waves don`t really start to drop significantly
until later Sunday afternoon into the evening hours. Cool
temperatures and a possible upwelling event (leading to much
cooler water temperatures) should both limit beach populations on
Sunday, but sunshine will still draw a crowd, so staying safe in
the water will be critical for this early-holiday weekend.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Beach Hazards Statement through Sunday evening for MIZ037-043-
     050-056-064-071.
MARINE...Small Craft Advisory until 10 PM EDT Sunday for LMZ844>849.

&&

$$

UPDATE...TJT
DISCUSSION...Laurens/AMD
AVIATION...04
MARINE...AMD