769
FXUS63 KGRR 291910
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
310 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 /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 137 PM EDT Mon Apr 29 2024

A line of showers is moving through the LAN terminal at present
and has just exited JXN. Thunder is not being observed within this
line, however conditions may briefly go MVFR as it passes through
LAN. Behind this line scattered showers are expected through the
afternoon and evening. An isolated thunderstorm is possible but
confidence is to low to include thunder in the TAFs at this time.
Brief drops to MVFR are possible within any showers. At MKG, the
moisture in place has led to patchy fog from the lake making it
into the terminal. Tower visbys have been reported in the 2-3 SM
range due to this but surface visbys should generally remain VFR.
As the cold front moves through this evening, drier air moves in
causing fog impacts to the terminal to end.

Expect ceilings to lift to above 5000 ft early Monday. Then above
10,000 ft near for MKG/LAN/GRR and scatter out for AZO/BTL/JXN
Tuesday morning. There are weak signals that patches of MVFR
clouds may develop towards Lansing and Jackson around 06-09z as
moisture pools ahead of the front but will not include MVFR cigs
at present due to lack of certainty. Look for southwest winds of
10-15 knots with gusts to 25 knots today become westerly at 5-12
knots tonight into Tuesday.

&&

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

The dense fog that was seen over much of the nearshore area has
diminished mainly south of Muskegon. We will drop the headline for
that region. Further north the fog could still be thick in places,
especially around Ludington. We will hold onto the marine dense
fog for those locations for a few more hours.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...Dense Fog Advisory until 8 PM EDT this evening for LMZ847>849.

&&

$$

DISCUSSION...MJS/Thomas
AVIATION...Thomas
MARINE...MJS/Thielke