093
FXUS63 KGRR 202336
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
736 PM EDT Sat Jul 20 2024

.KEY MESSAGES...

- Showers and storms possible north of I 96 Sunday afternoon

- Scattered Storms Possible Monday/Tuesday, Better Chance
  Wednesday

&&

.DISCUSSION...
Issued at 300 PM EDT Sat Jul 20 2024

- Showers and storms possible north of I 96 Sunday afternoon

 Fair weather will continue over the next 24 hours, however high
pressure will shift to the east as a moisture boundary associated
with an upper level trough treks from the south. Low level
moisture overnight should allow for another round of patchy
morning fog. While some high clouds should limit the spread there
could be some minor reductions to visibility Sunday morning.

 Any fog will clear out by mid morning as the before mentioned
weak boundary moves southwards. While dewpoints will increase
tomorrow leading to higher humidity, it should be dry enough for
any showers and storms to remain north of I 96 and begin to form
Sunday afternoon. Any storms are not expected to be severe with
around a half an inch or less of QPF expected.


- Scattered Storms Possible Monday/Tuesday, Better Chance Wednesday

Monday and Tuesday`s main impact will be in the form of scattered
afternoon convection. MUCAPE values exceeding 1000 J/kg will be
supportive of scattered afternoon thunderstorms. A weak shortwave
crossing northern MI will provide a slight forcing enhancement there
Tuesday. Otherwise, given the lack of notable synoptic features,
thunder chances will be largely driven by localized convergence such
as from the lake breeze. With bulk shear of 20 knots or less, storms
should mainly be pulsey in nature.

By Wednesday, a reinforcing mid-level wave drives a cold front
through the CWA in the later portion of the day bringing our best
chance of showers and thunderstorms. Where uncertainty, and the need
for monitoring comes in, is the extent of deep layer shear and
organized convection. Solid model consensus exists in 1000 + J/kg of
MUCAPE given the ample low-level moisture. The GFS/GEM and their
associated ensembles suggest a slightly stronger mid-level jet and
30-35 knots of shear which would support organized convection. The
ECMWF and its ensemble are weaker on the mid-level jet and by
extension shear. We will continue to watch overall trends and
possible support for stronger storms if confidence grows in the
GFS/GEM solution.

A bit of uncertainty as to how quickly the showers diminish on
Thursday as the ECMWF wants to close off the upper-low slowing its
exit while the other GEM/GFS keep an open wave and a faster exit.
Will have low PoPs mainly across the eastern CWA given the
uncertainty. Dry conditions expected Friday and Saturday as surface
and upper-level ridging take hold.


&&

.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 736 PM EDT Sat Jul 20 2024

No changes to previous thinking. VFR will predominate through at
least 12Z Sunday. As noted before, light winds will predominate
with MKG being a bit of an anomaly due to persistent SW flow off
Lake Michigan and an attendant risk for minor visibility
restrictions in fog due to slightly more humid air being pulled
onshore.

&&

.MARINE...
Issued at 315 PM EDT Sat Jul 20 2024

Light winds are expected due to high pressure overhead. Winds and
waves will increase a tad late Sunday as a weak cold front moves
south across the lake. At this time, waves should remain less than
3 feet. Waves will be highest north of Pentwater.

&&

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

&&

$$

DISCUSSION...Ceru/Thomas
AVIATION...TJT
MARINE...Ceru