996
FXUS63 KGRR 250018
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
818 PM EDT Tue Sep 24 2024

.KEY MESSAGES...

- Isolated Heavy Rain and Severe Potential into this Evening

- Dry Wednesday through Friday with mild temperatures

- Rain chances over the weekend and early next week

&&

.DISCUSSION...
Issued at 350 PM EDT Tue Sep 24 2024

- Isolated Heavy Rain and Severe Potential into this Evening

AN area of persistent heavy rain across Muskegon County has
resulted in 2 to 4 inches of rain today. More localized areas of
heavy rain are expected this evening.

Sfc low centered near southern Lake Michigan late this afternoon
will track northeast across Lower Michigan this evening causing
rain bands to pivot across the western zones. We have increased
QPF to account for excessive rainfall along the Lake Michigan
coast where hi-res models show the rain persisting this evening.

Meanwhile, cellular convection across northern Indiana will be
moving into the southern forecast area late this afternoon and
early evening where marginal instability is present as dew points
are peaking in the mid 60s. Deep layer shear is only about 20 to
25 knots, but 0 to 1 km helicity values are over 100 just north of
the warm front which is expected to stay south of 1-94. Main
threat is transient mesocyclones in isolated cells or embedded in
small line segments with brief tornado potential.

The severe threat will diminish this evening as sfc based
instability wanes. The low moves east with the steadier rain
exiting the eastern zones by midnight. Some lake effect rain
showers could persist near Lake Michigan into early Wednesday
before moving offshore out over the lake as the flow goes north.

- Dry Wednesday through Friday with mild temperatures

Once the current system moves entirely east of the area on
Wednesday, we will see a nice and dry period set up for the area
through Friday. That is because we will be under the influence of
the upper ridge building over the area from the west. This ridge
will be reinforced out ahead of the Tropical system that will be
moving toward the Ohio Valley. This results in plenty of
subsidence over the area, and moderating temperatures well into
the 70s.

- Rain chances over the weekend and early next week

The ridge will hold for a bit, but will eventually allow some of the
moisture up over the area beginning on Saturday, and lingering at
least into Monday.

The upper low that will be in place near Arkansas and will absorb
the tropical system, will eventually continue to rotate in the
region until a stronger system can boot it out. The upper low is
expected to largely stay SSW of the area through the week, but will
wrap moisture into the area from the SE and have short waves
rotating through our area.

Right now, it looks like there will be intermittent chances of rain
showers and a chc of storms for the weekend into early next week. It
does not look like a washout on any particular day, but could rain at
just about any time. Temperatures will stay mild during this time
frame as there is not really any cold air immediately available.

It is looking like that around the Tuesday time frame, that a
stronger northern stream system will dive SE out of Canada, and will
be strong enough to kick the weekend low out. That will involve
another chance of rain, and much cooler air behind it eventually.

&&

.AVIATION /00Z TAFS THROUGH 00Z THURSDAY/...
Issued at 818 PM EDT Tue Sep 24 2024

Have removed thunderstorms from the TAFs as lighting has been
sparse, mostly distant east of MKG and north of GRR. The heavy
rain showers in the vicinity of AZO have not produced lightning in
quite some time. Still good confidence in ceilings deteriorating
to IFR overnight, possibly LIFR in spots, then gradually improving
during the middle of the day Wednesday.

&&

.MARINE...
Issued at 350 PM EDT Tue Sep 24 2024

Waterspouts are possible this evening along convergent lines of
showers and isolated thunderstorms. Rain will be heavy enough to
lower visibility to below one half mile at times.

Northerly winds through Wednesday night should remain below 20
knots but may produce some choppy waves near Big and Little Sable
points. WInds go offshore on Thursday and Friday and waves in the
nearshore should remain at a foot or below.

&&

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

&&

$$

DISCUSSION...Ostuno/NJJ
AVIATION...CAS
MARINE...Ostuno