309
FXUS63 KGRR 030740
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
340 AM 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

&&

.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 /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 125 AM EDT Wed Jul 3 2024

An area of showers with embedded thunderstorms stretched from
western IL through northern Lower MI. The instability was
decreasing as these showers were advancing east into the TAF
sites here in southwest Lower MI. Based on the radar trends and
latest model data, we will keep thunder out of the TAF forecasts
for the remainder of the night, despite some slight instability
moving in. Low level moisture will be on the increase later
tonight and more so for Wednesday morning. Conditions are likely
to go down to MVFR and even a period of IFR for many of the TAF
sites. A cold front currently in MN will drop down into the TAF
sites here in MI Wednesday morning, weakening as it does. That
feature will likely generate some renewed showers/convection
Wednesday morning but based off of the limited instability, the
thunder risk at any particular TAF sites remains low. We will need
to monitor trends though. Drier air filters in behind the front
for Wednesday afternoon and that will likely support the cloud
bases rising with the clouds eventually scattering out.

&&

.MARINE...
Issued at 244 AM EDT Wed Jul 3 2024

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...Beach Hazards Statement until noon EDT today for MIZ037-043-050-
     056-064.
MARINE...Small Craft Advisory until 8 AM EDT this morning for LMZ844.
     Small Craft Advisory until noon EDT today for LMZ845>849.

&&

$$

DISCUSSION...CAS/MJS
AVIATION...MJS
MARINE...CAS