518
FXUS63 KGRR 182327
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
Issued by National Weather Service Green Bay WI
727 PM EDT Wed Jun 18 2025

.KEY MESSAGES...

- Severe storms this afternoon/evening

- Precipitation chances continue Thursday night into Friday

- Hot weather begins Saturday

&&

.DISCUSSION...
Issued at 313 PM EDT Wed Jun 18 2025

- Severe storms this afternoon/evening

Mesoscale Convective Vortex (MCV) currently crossing central IL
is the feature to watch. There is a growing rain shield developing
northeast of this low and that is likely more elevated in nature.
The MCV is expected to progress into Indiana and we will see a
peripheral threat for severe weather across our southern forecast
area particularly along the I-94 corridor where all threats are in
play, mainly between 4 and 10 PM.

There is a short fused hydro threat as well. Impressive rain totals
already have been observed across SE Lower MI and there is a
Mesoscale Precipitation Discussion (#0478) issued by WPC that
discusses the flood threat for southwest Lower MI as well. Please
refer to this product for further details.

- Precipitation chances continue Thursday night into Friday

As noted previously, we can expect wrap around precipitation
continuing overnight and at least into the first part of Thursday.
Areas south of I-96 could be dry by Thursday afternoon. However,
father north more towards US-10, there will be a persistent surface
trough juxtaposed with persistent conditional instability and
episodic weak upper PV advection in northwest flow. This justifies
continued PoPs, primarily north of I-96.


- Hot weather begins Saturday

Upper ridging becomes especially pronounced by Saturday with
attendant mid-level warming/capping. Sunday and Monday will likely
feature surface dewpoints in the lower 70s combined with highs in
the lower/mid 90s under clear skies. This will yield apparent
temperatures in excess of 100 both days. As noted previously, there
is a signal for a cold front to ease the situation in the late
Tuesday/Wednesday timeframe, but the forcing for this is
questionable. Therefore, it`s quite plausible that oppressive
conditions will persist into Wednesday and beyond.

&&

.AVIATION /00Z TAFS THROUGH 00Z FRIDAY/...
Issued at 726 PM EDT Wed Jun 18 2025

Generally poor flying weather is expected into Thursday morning.

An area of low pressure will be moving across southwest Lower
Michigan this evening before exiting across the thumb of Michigan
late tonight. While the strongest storms will have departed to the
east at the start of the taf period, the low pressure system will
bring periods of showers, MVFR visibilities at times, and ceilings
deteriorating to IFR.

Some showers will likely persist into Thursday morning. But flight
conditions are expected to gradually improve on Thursday morning
before becoming VFR in the 16-19z timeframe.

&&

.MARINE...
Issued at 313 PM EDT Wed Jun 18 2025

No headline concerns at this time. A surface low will pass east of
the waters, allowing for a brief period of northwest winds tonight.
However both the speed and duration will be limited and this will
curtail wave growth. The next appreciable chance for marine
headlines at this stage looks like Friday night where we will see
a response to the effects of persistent southerly flow.

&&

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

&&

$$

DISCUSSION...TJT
AVIATION...MPC
MARINE...TJT