-- Discussion containing changed information from previous version are highlighted. --
688
FXUS63 KGRR 151527
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1127 AM EDT Wed May 15 2024

.KEY MESSAGES...

- Drying Out Today, But Showers/Storms Return Late Thursday

- Showers/Storms Thursday night and Friday

- Chance of Stronger Storms Monday/Tuesday

&&

.UPDATE...
-- Changed Discussion --
Issued at 1127 AM EDT Wed May 15 2024

Still some clouds hanging on this morning, especially around JXN,
and now even some newer development of thicker mid clouds from
near and north of GRR across Mt Pleasant where old/lingering
deformation axis still exists. RAP 700 mb RH looks to have a
decent handle on this and suggests that these clouds may continue
to fill in while inching slowly southward this afternoon. That
implies more of a partly cloudy/partly sunny scenario this
afternoon for areas from GRR to the south and east, with sunny
skies prevailing farther to the north. Highs 70-75, with warmest
highs temps expected to be west of Highway 131 due to northeast
winds. However the immediate lakeshore may cool down later in the
day as winds become more NNW and a tad stronger for a time.
-- End Changed Discussion --


&&

.DISCUSSION...
Issued at 319 AM EDT Wed May 15 2024

- Drying Out Today, But Showers/Storms Return Late Thursday

The latest GOES low and mid level WV imagery shows a slow erosion
in moisture across central Lower Michigan this morning. RAP13
and GFS relative humidity layer (850mb-250mb) trends indicate
only a gradual decrease in moisture from N to S today. As such,
the expectation is for areas near and north of I-96 to see sun
break through by mid to late morning, but areas south of I-96 (and
especially toward I-94) may take until early to mid afternoon for
clouds to erode. Any leftover light showers and sprinkles are
expected to end by mid morning across our far southern forecast
area near I-94.

For Thursday, a weakening upper trough will push into the Great
Lakes region. Synoptic forcing for ascent will somewhat be there
with the upper trough and a decent ULJ, though GFS/HRRR model
soundings show equilibrium levels not getting much above
500mb-400mb during the daytime, indicative of modest convective
potential. Low level moisture advection may take some time to
materialize across the region, impacting areas near and south of
I-96 first. 00z HREF guidance does show some marginal SB CAPE
possible in this area, perhaps a few hundred J/kg by late
afternoon. There could be a scattering of showers and a few
thunderstorms possible Thursday afternoon especially near and west
of U.S. 131, but it appears most precipitation will hold off
until after dark.

- Showers/storms Thursday night and Friday

We`ll have several chances for showers and thunderstorms during the
period. However, much of the weekend looks dry.

Thursday night and Friday will see the highest chances for rain as a
cold front moves across the cwa. Low to moderate instability is
progd with this system with MUCAPE values in the 500-1k j/kg range.
Isolated to scattered storms are likely during this time frame.
Shear values in the 35-40 kt range suggest that a few storms may
skew toward being strong late Thursday night and Friday morning,
however early morning timing usually doesn`t bode well for stronger
storms and the short wave accompanying the front isn`t all that
impressive either.

- Chance of stronger storms Monday/Tuesday

The weather early next week bears watching. West southwest flow
aloft will bring several short waves from the Plains into the Great
Lakes and each will have an impressive surface low. The first low
will develop Sunday night over KS/IA and then track toward Lower MI
Monday. The GFS isn`t as aggressive as the Euro is but develops
showers/storms near a wave on a frontal boundary that moves across
the cwa Monday. Most of the instability and dynamics remain south of
the cwa with the GFS, but nonetheless produces some rain.

The bigger deal may be Tuesday as both models produce an impressive
surface low over the MO Valley and push a warm front toward the cwa.
Additionally, 40-50kts shear develop in response to a strong LLJ to
the south and higher mid level winds poking in from the southwest.
This scenario has the potential for stronger storms.

Highs will be in the 70s through the period.

&&

.AVIATION /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 653 AM EDT Wed May 15 2024

No changes to the going forecast. Showers have ended at the
terminals. However, there remains some MVFR stratocu at JXN. That
should lift within the next few hours. Otherwise, clouds will thin
today and VFR conditions are expected through the rest of the
period.

&&

.MARINE...
Issued at 319 AM EDT Wed May 15 2024

Broad NE flow over Lake Michigan will likely turn N/NW after 18z,
leading to an uptick in wave action across all zones, especially
south of Pentwater. Waves may increase to 2-3 ft by this
afternoon. Conditions do not look to warrant a SCA at this time.
From Thursday into the first part of the weekend, wave action will
likely hold in the 1-2 ft range.

&&

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

&&

$$

UPDATE...Meade
DISCUSSION...Hoving/99
AVIATION...04
MARINE...Hoving