449
FXUS63 KGRR 130549
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
149 AM EDT Sat Jul 13 2024

.KEY MESSAGES...

- Chances for Storms Saturday Night to Tuesday

- Weekend heat followed by cooling next week

&&

.UPDATE...
Issued at 958 PM EDT Fri Jul 12 2024

Through 930 PM, the Grand Rapids airport was the unexpected
beneficiary of 0.63 inches of rain. Here at the office,
immediately north of the airport, we received about 0.55 inches of
rain. The Kalamazoo airport had a similar encounter with an
isolated shower, resulting in nearly a quarter of an inch of
precipitation. These showers were largely driven by a lake breeze
front. We never did see any pulses or flashes associated with this
activity.

Expect precipitation to dissipate well before midnight beneath
pronounced subsidence noted on satellite water vapor imagery. We
already expected fog to be an issue Saturday morning southeast of
Grand Rapids; however, the threat has grown in and around Grand
Rapids as well as the Kalamazoo area based on the humidifying
effects of the rain that recently fell. Not expecting anything
that would rise to the level of a widespread dense fog advisory,
but visibilities could be a bit dodgy in spots Saturday morning,
especially if larger scale subsidence persists.

&&

.DISCUSSION...
Issued at 321 PM EDT Fri Jul 12 2024

- Chances for Storms Saturday Night to Tuesday

An upper trough will provide enough instability for scattered
showers and thunderstorms this evening. A few isolated areas of
heavy rain will be possible until an hour or two after sunset when
the storms are expected to diminish and end by midnight.

Upper ridging to our west leads to northwest flow aloft with several
shortwaves riding the crest of the ridge into the Great Lakes region.
This will result in several chances for active weather this weekend
into early next week. The main windows of time for strong to severe
storms will be late Saturday night to Sunday morning, and late
Sunday night to early Monday.

Starting Saturday night to early Sunday, ongoing convection
originating front the Northern Plains early in the afternoon will
track east towards lower Michigan through the night. Fueled by a
pronounced 850mb low level jet and strong instability and deep layer
shear upstream, storms may maintain in intensity as they cross the
lake into Michigan in the early morning hours Sunday.

For Sunday night to Monday, storm development will be largely
dependent on how storm activity evolves the previous night.
Regardless, the environment will be primed for renewed storm
activity Sunday evening. MUCAPE recovers to 3000+ J/kg with deep
layer shear of 40 to 50 knots in the evening. While uncertainty
exists on Sunday evening storm evolution, know the potential is
there and it could be a day to monitor.

A surface boundary will setup somewhere across the state late Monday
into Tuesday resulting in renewed chances for precipitation. Some
strong storms will be possible along this frontal boundary, but
current confidence for severe weather for this time period is low.

- Weekend heat followed by cooling next week

Amidst all the active weather, conditions will be hot and humid.
850mb thermal ridge rides overhead pushing temps to 20 to 21C
translating to surface highs to 90 degrees Sunday and Monday while
dewpoints push into the low to mid 70s. Apparent T`s in the upper
90s to near 100 Sunday and Monday, then expect a gradual cooling
period Tuesday as upper troughing pushes a cold front through our
area. Highs in the low to mid 80s Tuesday, then back into the 70s
Wednesday through Friday.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 149 AM EDT Sat Jul 13 2024

The main and really only aviation concern in the 24 hour TAF
period of 06Z Saturday to 06Z Sunday is fog and possibly stratus
this morning.

Isolated showers occurred this past evening, two of which hit the
GRR and AZO airports. Given that fresh moisture on the ground,
clear skies and light winds we expect fog to form at both of those
sites. In fact given the amount of rain that has fallen over the
bulk of the area in the last week, we see fog formation at all
sites this morning with the exception being MKG. MVFR visibilities
should be in place at most TAF sites by 09Z with IFR likely
settling in during the 10Z to 13Z time frame. A rapid clearing
should occur given the shallow nature of tonight`s fog. Stratus
formation is difficult to say, but it is certainly possible this
morning.

Otherwise, VFR weather is expected from mid morning through the
rest of the TAF period. More active weather, showers and
thunderstorms are expected to develop late tonight just beyond
this TAF period (06Z to 12Z Sunday).

Winds will be light and variable this morning becoming southwest
at 5-10 knots today.

&&

.MARINE...
Issued at 321 PM EDT Fri Jul 12 2024

Winds and waves will be relatively light into next week but there
could be rounds of strong thunderstorms on Saturday night and
again Sunday night into Monday that could bring winds greater than
30 knots and locally higher waves.

&&

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

&&

$$

UPDATE...TJT
DISCUSSION...Ostuno/Thielke
AVIATION...Duke
MARINE...Ostuno