508
FXUS63 KGRR 141906
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
306 PM EDT Mon Sep 14 2026

.KEY MESSAGES...

- Several rounds of showers and Storms tomorrow

- Chances for Rain through the week


&&

.DISCUSSION...
Issued at 258 PM EDT Mon Sep 14 2026

- Several rounds of showers and Storms tomorrow

Forecast remains fairly consistent. There will be two rounds of
showers tomorrow. The first will be early in the morning. It will
move across Lower Michigan from the northwest and move eastward with
heavy rain possible. Severe winds not expected but there is the
potential for strongest storms to overperform.

Another line in the afternoon and evening will trek across
Southern Michigan along the warm air advection. The best
instability will be in IN and OH. However, due to the significant
PWATS, upwards of 2 inches, CAPE`s upwards of 1500 J/kg, lapse
rates of 7 C/kg through the mid to low levels along with strong
low level wind shear and there will be a chance for convection
along and south of the I 94 corridor could become strong to
severe. SPC continues to have a marginal risk through this region.


- Chances for Rain through the week

 There remains some question about where the frontal pattern
shifts this week. If it shifts/expands to the north then quite a
bit of southern lower Michigan could receive multiple rounds of
showers and storms through Thursday. The zonal flow will keep mid
level moisture over the area. If there is enough warm air
advection, along with any mid level short wave amplification, and
areas could receive periods of heavy rain. NAEFS shows a
prolonged period of anomalous moisture along the southern half of
lower Michigan. Latest NAEFS PWATs along the I 96 corridor could
be around 1.25 inches and increase to 2 inches in northern IN.
This moisture boundary remains entrenched over the area through
the week and latest ensembles has it shifting northward towards
the end of the week. If it shifts southward, then much of the
region will remain dry.

Another system will lift into the area this weekend and could
bring additional shower and thunderstorm chances Saturday.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 205 PM EDT Mon Sep 14 2026

VFR with light winds are expected through evening. Clouds start to
thicken below 10,000 feet after 00 Z and through the night, from
northwest to southeast. Initially some light rain showers or virga
may push in, then instability at around the 7,000 foot cloud layer
begins to build enough for a chance of thunderstorms embedded
within the batch of rain during the morning hours Tuesday. South
of the batch of rain or thunderstorms, there may be a period of
LLWS late tonight / early morning.

&&

.MARINE...
Issued at 258 PM EDT Mon Sep 14 2026

Conditons deteriorate tonight into Tuesday as an approaching surface
low deepens increasing southerly flow. Enough of a signal for 35-40
knot gales exists north of Holland to hoist a Gale Warning, with a
Small Craft Advisory south of Holland for 22-33 knot gusts. Gales
persist into Tuesday morning with conditions hazardous to small
craft continuing into Tuesday night. Will also hoist a Beach Hazards
Statement from Allegan County north for waves as high as 12 feet.
 Due to the refracting waves and strong southerly flow, have
expanded the beach hazards to include Van Buren county. The
southerly flow could shift just enough that waves miss South
Haven, however given latest trends, there is enough concern that
waves could grow to the 3-5 ft range bringing a high swim risk.


&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Beach Hazards Statement from 10 PM EDT this evening through
     Tuesday evening for MIZ037-043-050-056.
     Beach Hazards Statement from 10 PM EDT this evening through
     Tuesday afternoon for MIZ064-071.
MARINE...Small Craft Advisory from 10 PM this evening to 5 PM EDT Tuesday
     for LMZ844-845.
     Gale Warning from 10 PM this evening to 8 AM EDT Tuesday for
     LMZ846>849.

&&

$$

DISCUSSION...Ceru
AVIATION...CAS
MARINE...Ceru