438
FXUS63 KGRR 171029
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
629 AM EDT Thu Sep 17 2026
.KEY MESSAGES...
- Scattered Showers and Isolated Storms This Morning
- Heavy Rain Possible This Saturday
&&
.DISCUSSION...
Issued at 257 AM EDT Thu Sep 17 2026
- Scattered Showers and Isolated Storms This Morning
Regional composite radar imagery shows convection developing
associated with a Low-level jet overrunning the stationary front to
our south. The best coverage will be south, however rain showers are
possible into this morning, especially south of I96. Instability is
pretty marginal but cannot rule out isolated storms. Conditions then
dry out later today into Friday as high pressure takes over as the
main driver of our weather.
- Heavy Rain Possible This Saturday
On the heels of this breif dry window comes widespread precipitation
Friday Night into Saturday. A ample southerly LLJ forces the front
south of us back north as a warm front. In conjunction with marginal
instability and PWATs near 2" this is a favorable setup for high
rainfall efficiency. Some question based on low placemenet and
convective track as to where exactly the heaviest rain falls,
however heavy rain is likely. High confidence in rainfall north of
1" across much of the area, with NBM probabilities of > 2" north of
60% in spots. Overall the slight ERO from WPC remains in good shape.
&&
.AVIATION /12Z TAFS THROUGH 12Z FRIDAY/...
Issued at 628 AM EDT Thu Sep 17 2026
Low stratus has set in across the area. Most sites are IFR, with
LIFR at AZO/BTL with patchy fog across those terminals as well.
Conditions will slowly improve through the day, with the
southernmost TAF sites (AZO/BTL/JXN) being last to scatter out to
VFR this evening. Likely to be some adjustments needed to exact
improvment times due to dependence on upstream showers providing
pockets of enhanced moisture. Winds will be predominantly from the
east to northeast today.
&&
.MARINE...
Issued at 257 AM EDT Thu Sep 17 2026
Can`t rule out an isolated thunderstorm over the southern waters
tonight, however chances are low. The next hazard of note is Friday
Night into the weekend. Increasing winds will support gusts aoa 22
knots, though the easterly flow does favor the better waves
remaining over the open waters. A Small Craft Advisory may be
needed. Thunderstorms are also possible over the waters Saturday.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...None.
&&
$$
DISCUSSION...Thomas
AVIATION...Thomas
MARINE...Thomas
NWS GRR Office Area Forecast Discussion
