541
FXUS63 KGRR 050240
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1040 PM EDT Sat May 4 2024

.KEY MESSAGES...

- Showers moving east through the area tonight

- Dry Monday, then chances for showers/storms

&&

.UPDATE...
Issued at 1039 PM EDT Sat May 4 2024

A cold front is situated north/south out over Lake Michigan at
02Z. Showers and a few embedded thunderstorms remain along and
ahead of the front moving through Western Lower Michigan. Winds
with the line as it came ashore were generally in the 30-40 mph
range. Instability (MUCAPE) ahead of the line is on the order of
500 j/kg at this point and it should be continuing to lower from
this point on with the loss of daytime heating. So, we expect
showers to continue to move from west to east across the area
tonight with an isolated thunderstorm also possible. Not expecting
anything close to severe given weak instability and shear. The
front and precipitation should be clearing east of the forecast
area at KLAN and KJXN around 12Z. Low clouds will fill in once
again tonight, but visibilities should stay manageable.

&&

.DISCUSSION...
Issued at 255 PM EDT Sat May 4 2024

- A few showers,maybe some thunder this evening, quiet Sunday

Showers/thunderstorms will try to get their act together this
afternoon in Illinois and Wisconsin will move across Lake Michigan
and western Indiana early this evening along with a weak cold front.
Models are indicating this line will struggle to remain organized
as it moves east and considering decreasing elevated instability
overnight - it is looking more like a broken weakening line of
showers/thunderstorms that may result in quite a bit of the area
seeing no rain at all. If any storms do hold together, not out of
the question that some small hail will be possible though this
doesnt look that likely at this time.

Any lingering light showers should be off to the east by daybreak
Sunday. High pressure begins to build in Sunday with stubborn cloud
cover lingering through much of the day. This could result in cooler
temperatures than Saturday but dry weather should result regardless.

- Dry Monday, then chances for showers/storms

Transient high pressure over Lower MI Monday will produce sunny
skies and mild temperatures with highs around 60. An upper low over
the northern Plains will influence our wx the rest of the week as
pieces of energy will rotate through the flow and move across the
region.

Clouds will increase Monday night with storms likely Tuesday when a
warm front lifts north late in the day. Moderately strong dynamics
look to be develop late Tuesday as a LLJ moves over the region and a
mid level speed max aims at Lower MI from the southwest. H85-h5
lapse rates also climb to around 7c/km during this time frame. Given
the warm frontal interaction, strong shear and decent helicity, all
forms of severe wx look to be possible from late Tuesday afternoon
through Tuesday evening; SPC has highlighted the southwest cwa for a
severe wx risk.

Once the warm front moves through late  Tuesday night there may be a
lull in precipitation until the next wave over the central Plains
moves toward the region late Wednesday through Thursday night. More
showers/storms are expected then. The upper low isn`t progd to move
through the state until late Saturday, so unsettle conditions will
continue through the first half of the weekend.

&&

.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 814 PM EDT Sat May 4 2024

Still expect a relatively narrow band of showers to traverse the
terminals overnight followed by IFR ceiling restrictions that
slowly climb to MVFR after 12Z. Guidance suggests that brief LIFR
ceiling restrictions lasting on the order of an hour or so will
be possible at many of terminals, presumably associated with the
passage of the cold front. This idea is not supported by all of
the available guidance nor is timing certain. Hence, did not
attempt to represent this quick departure in the terminals.

Did include a brief window of VCTS for the KAZO terminal based on
ongoing activity upstream near Chicago. VCTS may be required
before 03Z at MKG as well. However, current expectations are for
thunderstorms over Lake Michigan to weaken or dissipate prior to
reaching eastern Lake MI, which is why we were reluctant to
include VCTS at MKG just yet. There is a lesser, but nonzero,
chance of needing to include VCTS at GRR later tonight in the 05Z
timeframe.

&&

.MARINE...
Issued at 300 PM EDT Sat May 4 2024

Winds this evening still expected to nudge up this evening as a cold
front works across Lake Michigan. A few showers and some thunder
possible but showers/storms should be weakening as they approach the
shoreline. Behind the front north/northwest flow should increase a
little but at this time looks like it should peak out 15-20kts and
will continue to hold off on an advisory.

&&

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

&&

$$

UPDATE...Duke
DISCUSSION...04/Maczko
AVIATION...TJT
MARINE...Maczko