155
FXUS63 KGRR 120141
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
941 PM EDT Thu Jul 11 2024

.KEY MESSAGES...

- Occasional showers and Thunderstorms into Early Next Week

- Hot and Humid Weekend to Early Week

&&

.UPDATE...
Issued at 940 PM EDT Thu Jul 11 2024

The scattered convection that has brought areas of torrential
rainfall and gusty winds are finally ending. The storm outflows
from these storms would interact with the warm, humid air mass to
allow for thunderstorms that, due to no driving winds aloft, would
be slow moving until the core fell apart and the outflow would
spark another round of storms. There was a report of just over an
inch of rain in East Grand Rapids. The boundary interactions that
have kept these storms going will not be enough as any convection
will weaken as after sunset the region will lose instability.
 However from the latest water vapor satellite imagery, it shows
the upper low will be moving over Southern Michigan overnight that
will bring PV anomalies that should keep periods of showers going
into Friday morning, especially along and south of the I 94
corridor.

&&

.DISCUSSION...
Issued at 352 PM EDT Thu Jul 11 2024

- Occasional showers and Thunderstorms into Early Next Week

An upper low moving in from the west opens up into a trough
on Friday and we will see a continuation of mid level lapse
rates, sfc based instability and moisture sufficient for diurnally
enhanced showers and thunderstorms into Friday afternoon. Shear
profiles are weak with 20 knots or less of deep layer shear, so
organized storms are not expected through Friday night.

The possibility of severe storms approaching Lower Michigan
increases after Saturday as upper ridging over the western US and
subtle troughing over the eastern US places the Great Lakes
region in perfect position for northwest flow aloft with several
shortwaves triggering active weather. While there are a few
chances for showers and storms Saturday through Tuesday, the main
window to monitor for will be Sunday night to early Monday as a
boundary approaches lower Michigan from the Plains. Strong to
extreme instability to our west along with adequate deep layer
shear will support a severe threat including the potential for a
severe wind producing MCS that may move into lower Michigan late
in the night. There remains uncertainty on storm track and
evolution, though, as the GFS moves convection towards the UP
while the Euro favors a southerly track pushing the MCS towards SE
Wisconsin and far SW Michigan. In general, there is the potential
for impactful weather during this time frame, but there remains
uncertainty on track due to subtle mesoscale features that can`t
be resolved just yet.

- Hot and Humid Weekend to Early Week

Temperatures will be on the rise through the end of this week and
into next weekend as an 850mb thermal ridge moves overhead. High
temperatures in the low 80s to through tomorrow, then temps warm to
the upper 80s Saturday and near 90 Sunday and Monday. Dewpoints
surge into the 70s Sunday and Monday resulting in Apparent Temps in
the mid to upper 90s. Expect a gradual cool down into mid week as
high pressure builds back into the region.

&&

.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 759 PM EDT Thu Jul 11 2024

Isolated thunderstorm cells will flirt with the GRR terminal
through sunset, possibly producing a brief heavy downpour/vsby
reduction along with some gustier winds. Otherwise VFR conditions
expected tonight with the possibility of some late-night
light fog (MVFR/3-5 mile vsby).

The risk for dense fog (IFR or lower conditions) overnight looks
low at this time since more clouds than last night are
anticipated and there`s a bit more wind just above the surface.

The threat for rain showers never completely goes away overnight
into Friday since there`s an upper low in the vicinity. Those
showers seem to favor the area south and east of GRR later
tonight and Friday per latest guidance.

&&

.MARINE...
Issued at 352 PM EDT Thu Jul 11 2024

Winds and waves are not expected to be hazardous through the
weekend, although there is the chance of thunderstorms with
locally higher winds and waves during this time.

&&

.HYDROLOGY...
Issued at 352 PM EDT Thu Jul 11 2024

River flood warnings continue to be the focus in the wake of the
recent heavy rain. Here are the warnings that were issued,
canceled or extended today:

A flood warning was issued for the Red Cedar River at East
Lansing for expected minor flooding through the next couple days.

The warning for the Sycamore Creek at Holt has been extended,
while the warning for Eagle has been cancelled as the crest is no
longer forecast to reach flood stage. Flooding is continuing at
the Portage River at Vicksburg and the warning will remain in
effect.

&&

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

&&

$$

UPDATE...Ceru
DISCUSSION...Duke
AVIATION...Meade
MARINE...Ostuno
HYDROLOGY...Ostuno