471
FXUS63 KGRR 030644
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
244 AM EDT Wed Jul 3 2024

.KEY MESSAGES...

- Showers with scattered thunderstorms tonight into tomorrow

- Strong storms remain possible for Friday

- Unsettled weather at times next weekend and early next week

&&

.UPDATE...
Issued at 1058 PM EDT Tue Jul 2 2024

Bumped up POPs across the northern half of the forecast area the
next few hours per radar trends. Expect the showers and storms to
persist but diminish in coverage after midnight given lack of
upper level support and instability. At least chance POPs through
the overnight look good as the cold frontal passage doesn`t occur
until Wednesday afternoon.

&&

.DISCUSSION...
Issued at 324 PM EDT Tue Jul 2 2024

- Showers with scattered thunderstorms tonight into tomorrow

Scattered showers continue to stream through the region, mainly
along and north of I 96. These showers will continue to move to
the northeast as the incoming trough pushes any remaining high
pressure eastward. A stronger line of showers and storms out ahead
of a frontal system will move through tonight into tomorrow
morning. None of the storms are expected to become severe,
especially given the lack of dynamics and the time of day.
 Dry air will move in behind the exiting convection with clearing
skies mid to late Wednesday.


- Strong storms remain possible for Friday

Most of the area should stay dry on Thursday, before shower/storm
chances move back in for Friday.  We will be in between systems for
the most part on Thursday. The front that moves through on Wednesday
will slip far enough south of the area to take most if not all of
the rain chances with it. There is a small chance the I-94 corridor
sees a brief shower on the northern edge of any complex riding along
the front.

There is fairly good agreement that we will have a potential period
of stronger storms on Friday. Models are in fairly good agreement in
bringing a healthy short wave and associated sfc front through the
area on Friday afternoon. The low level jet associated with the
system will help to bring a warmer and more humid air mass (implying
instability) up over the area ahead of the upper and sfc features.

In addition, an upper level jet max with the upper wave will help to
provide plenty of deep layer shear for the storms that are looking
increasingly likely to form. There are still a lot of details that
have to be worked out, (exact timing, low level flow, etc...) but it
is something we will continue to keep our eye on.

- Unsettled weather at times next weekend and early next week

The system moving through Friday looks to be the beginning of a
general pattern change that is expected to hold over the Upper
Midwest and Great Lakes into next week. We will see general long
wave upper troughing settle in over the area as a fairly extensive
upper ridge will set up over the western half of the country.

The period from Saturday through next Tuesday will see chances for
showers and storms at times. These chances will come via short waves
that will be rotating around the long wave trough. These types of
scenarios are difficult to pin down this far out due to the
evolution of the upper low and where and when if it closes off or
not, and the timing of the short waves.

Generally speaking, temperatures should be kept down slightly with
the lower heights expected. It does not look to be too cool, and
could still be warm if the sfc flow ends up from the south. Even
with multiple chances of rain expected off and on, much of the time
will be dry.

&&

.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.

&&

$$

UPDATE...Ostuno
DISCUSSION...NJJ/Ceru
AVIATION...MJS/Thielke
MARINE...CAS