982
FXUS63 KGRR 031715
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
115 PM EDT Wed Jul 3 2024

.KEY MESSAGES...

- Chance of Passing Showers Today Then Clearing Clouds

- Warm and Partly Sunny Independence Day

- Risk for a Period of Strong Storms Friday

&&

.UPDATE...
Issued at 1031 AM EDT Wed Jul 3 2024

No changes to the current forecast are planned. The main forecast
concern with the afternoon update will be regarding the potential
for strong/severe convection Friday.

&&

.DISCUSSION...
Issued at 340 AM EDT Wed Jul 3 2024

- Chance of Passing Showers Today Then Clearing Clouds

A weak cold front passing through the area this morning, along with
remnant low-level moisture and meager elevated instability, may
touch off a few showers (slight chance of isolated thunderstorm).
By late in the morning, the chance will shift south and east of
Grand Rapids toward Jackson. Most of the clouds are likely to clear
away from NW to SE this afternoon, and deeper mixing will help
temperatures climb higher than they were yesterday.

- Warm and Partly Sunny Independence Day

In between upper-level shortwave troughs on the 4th of July, there
will be a diffuse surface pressure field resulting in light winds,
while temperatures climb to slightly warmer than normal. The maximum
heat index should stay below 90. Skies will be partly cloudy as
high clouds stream in from convection to our west and a few cumulus
clouds may bubble up. Some models develop isolated showers late in
the day but the chance is about 10 percent for any given spot.

- Risk for a Period of Strong Storms Friday

Models continue to advertise a closed 500 mb low tracking through
Lower MI during the afternoon. A stronger mid level jet streak on
the south side of this system pivots through the CWA enhancing the
deep layer shear.  Surface instability plots show the atmosphere
destabilizing during the late morning into the afternoon hours.
Generally the models indicate that scattered convection will develop
in the late morning to early afternoon hours before shifting the
action east of the CWA by mid afternoon.  The deep layer shear
projections support organized convection, however the instability is
shown to be somewhat limited.  Ensemble surface based CAPE
projections are mostly under 1000 J/kg which could be a limiting
factor for the amount and strength of any convection that does
develop. Close monitoring will be needed as we get closer to this
period. For now, we will continue to feature relatively high POP`s
for the late morning into the afternoon period.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 113 PM EDT Wed Jul 3 2024

Primarily VFR expected after 18z as cloud bases rise, though
isolated MVFR pockets cannot be ruled out through 21z. Ceilings
then become indefinite as high pressure overnight causes only SCT
cirrus. There are signals for for at MKG early Thursday as better
moisture arrives in combination with flow off the lake but
confidence is to low to add restrictions so went with VCFG to
highlight the best window. BKN clouds above 10kft arrive along I94
mid morning Thursday however any showers remain south of the
terminals. Westerly winds around 10 knots expected today calming
tonight to at or below 5 knots and remaining there through the
rest of the TAF window.

&&

.MARINE...
Issued at 1031 AM EDT Wed Jul 3 2024

Update...

Will let the Beach Hazards and Small Craft Advisory expire at
noon, although observations strongly suggest we`ve already dropped
below hazardous criteria.

Previous discussion follows...

This forecast is lower than usual confidence for small craft and
swimming hazards this morning, but at the very least it`s likely
that moderate swim risk will be present along many beaches, with a
fair enough possibility for high swim risk to issue a Beach Hazards
Statement through noon.

Ongoing Small Craft Advisory for gusts over 22 knots will be
extended later into the morning as the wave field responds to
briefly stronger southwesterly winds anticipated over the next few
hours and lingers for a few more hours after the winds relax. Models
have been varied in their solutions for early this morning regarding
where, how strong, and for how long the stronger southwesterly
surface winds will be. Stronger winds are present just 1000 feet
above the lake, but it seems they will not fully mix down without
the help of rain falling into the dry air at 1000 feet and cooling
it down in tandem with the passing cold front. Even the most
aggressive models relax the winds substantially no later than 8 or 9
AM, so any waves or currents hazardous enough for boats or swimmers
should be diminishing by noon if not earlier.

Independence Day will feature light winds and waves 1 foot or less.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...None.

&&

$$

UPDATE...TJT
DISCUSSION...MJS/CAS
AVIATION...Thomas
MARINE...TJT/CAS