897
FXUS63 KGRR 241951
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
351 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 /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 148 PM EDT Tue Sep 24 2024

We are looking at this forecast period being quite impactful with
IFR-VLIFR expected most of the time at most of the sites.

Rain has been most widespread at KMKG so far today, with scattered
showers elsewhere. IFR conditions have moved in over all of the
terminals except at KLAN in an isolated hole. The IFR and lower
conditions will persist this afternoon and tonight. A line of
stronger showers and a few storms will lift up into the area later
this afternoon and this evening. These will likely bring some
tempo lower conditions under heavier rain.

Behind the showers and storms, a few scattered showers will
persist overnight. The latter half of the night will see fog and
even lower clouds develop. These conditions will persist through
Wednesday morning, before eventually improving Wednesday
afternoon.

&&

.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...NJJ
MARINE...Ostuno