892
FXUS63 KGRR 300010
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
810 PM EDT Mon Apr 29 2024

.KEY MESSAGES...

- Scattered Showers/Storms into early evening

- Best Chance for Showers and Storms Thursday into Friday

- Above Normal Temperatures for Early May

&&

.DISCUSSION...
Issued at 258 PM EDT Mon Apr 29 2024

- Scattered Showers/Storms into early evening

One batch of showers was pushing through the Lansing to Jackson
region at this time. ML CAPE values were relatively low in our CWA
and that has limited the thunder risk potential. The coupled upper
level divergence/low level convergence area along this line of
showers was pushing northeast of the CWA. Projected surface based
instability(<500 J/kg) and lift through the remainder of the
afternoon hours suggest only a limited potential for
showers/storms exists going into the early evening hours. Most of
this lift will be associated with the surface cold front that
pushes in from the west. Isolated showers/storms could develop
near and ahead of this front. Also, there is one batch of
showers/storms in southeast IL/west central IN will likely clip
the area southeast of a Battle Creek to Lansing line over the next
few hours and that is the region where we will feature the
highest probabilities for measurable precipitation this afternoon.

- Best Chance for Showers and Storms Thursday into Friday

Wednesday looks to be dry for West Michigan as any minimal rain
chances Tuesday night quickly evaporate after daybreak. The next
notable chance of rainfall across West Michigan is Thursday into
Friday. A warm frontal boundary lifting north across the state
provides some potential for showers during the day on Thursday,
especially closer to the low towards Muskegon and Ludington.

Precipitation becomes more widespread Thursday Night into Friday as
a cold front drops across the region with a shortwave off of the
parent trough moving through. Depending on when the front comes
through, we will need to monitor for the chance of thunderstorms.
The NAM (which is just coming into range) along with the GFS, both
suggest most unstable CAPE values in excess of 1000 J/kg are
possible Thursday afternoon.

Predictability in the longwave pattern decreases notably into next
weekend. Cluster analysis shows a trough somewhere in the vicinity
of the region Saturday into Sunday, however there are discrepancies
in the amplitude of this feature and whether deeper troughing
directly affects lower Michigan. In one camp you have most GEPS
members along with approximately 40 percent of the GEFS/EPS members
suggesting a greater amplitude trough and by extension better
forcing for precipitation, making up about 50 percent of the grand
ensemble. On the other hand, the other approximately half of the
grand ensemble supports a more zonal pattern with the better height
falls staying out of the area. This would support lower
precipitation chances across West Michigan. Given the uncertainty,
will leave the current 30% PoPs from the NBM as is.

- Above Normal Temperatures for Early May

Highs in the 70s are expected for the long term period. The warmest
day will be Thursday as southwest flow causes 850mb temps to rise
into the 12-16C range. NBM max temperature probabilities suggest a 50
percent or more chance of exceeding 80 degrees Thursday south of M46.
Low temperatures should generally be in the 50s. This will be above
our normals of mid to upper 60s for early May highs and mid 40s for
lows.

&&

.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 810 PM EDT Mon Apr 29 2024

Mainly VFR is expected, exceptions being MVFR ceilings near and
south/east of JXN the next few hours and also a couple hour period
of MVFR ceilings possible tonight with a cold front passing
through everywhere else. Winds become west with gusts 16 to 20
knots during the day Tuesday, with VFR likely.

&&

.MARINE...
Issued at 810 PM EDT Mon Apr 29 2024

Dense fog in the nearshore has cleared up, and south winds this
evening will shift westerly overnight with passage of a cold
front. During the day Tuesday, west winds will back southerly late
in the day. The cooler waters of Lake Michigan, compared to the
relatively warmer air mass, will maintain a stable marine layer
and prevent stronger winds aloft from gusting over the lake.

&&

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

&&

$$

DISCUSSION...MJS/Thomas
AVIATION...CAS
MARINE...CAS