341
FXUS63 KGRR 180615
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
215 AM EDT Mon May 18 2026
.KEY MESSAGES...
- Severe threat with possible tornadoes remains through mid evening
- Periodic showers/storms possibly strong to severe through Tuesday
- Much quieter and seasonable mid-late week
&&
.DISCUSSION...
Issued at 142 PM EDT Sun May 17 2026
- Severe threat with possible tornadoes remains through mid evening
All of the ingredients remain in place for a possible severe event
late this afternoon and evening for our area north of I-96. As
mentioned earlier, we are concerned with an MCV over Wisconsin that
looks to interact with a warm front that is draped over the heart of
the forecast area. As of 17z/1 pm EDT, the front extended from near
the Muskegon/Oceana county border, to Newaygo and Mecosta counties,
to just south of Alma.
The MCV over Wisconsin is already producing severe weather with
Severe Thunderstorm Warnings and Tornado Warning there.
Extrapolating this line of storms has it hitting Oceana and Mason
Counties near Little and Big Sable Points around 4 pm. This
trajectory looks very favorable for interacting with the front. The
MCV will help to bump the Effective Deep Layer Shear values up to
around 50 knots, right near the front where plenty of low level
shear is present.
The threat looks to be through about 00-01z/8-9 PM EDT before the
MCV moves out. This is likely to give the area a lull in the
shower/storm activity for much of tonight.
- Periodic showers/storms possibly strong to severe through Tuesday
The sequence of events is a bit uncertain then for Monday through
Tuesday as multiple rounds of storms will be associated with the
main sfc front and waves along it. What we do know is that we should
be in the warm sector from Monday through at least early Tuesday. We
could see the leftovers of a line of storms come in from our WSW
very late tonight and Monday. This then would potentially affect
additional development of convection, or subdue it with other
convection that would try to form. We are thinking that the main
threats Monday would be wind and hail. We do not have good low level
shear present on Monday to support any tornado threat.
One signal we do have for a better bet of convection will be late
Monday night into Tuesday. This would the development of convection
to our WSW, and try to bring it in here Tuesday morning. Then,
depending on that convection, we will have the potential for frontal
convection Tuesday afternoon and evening. The evolution of that will
depend on how much early morning convection would affect the area,
and limit destabilization ahead of the front. The air mass ahead of
the front could be favorable for severe with sufficient
destabilization, and 40-50 knots of deep layer shear. Low level
shear is also favorable with a 45 knot low level jet core over the
area.
- Much quieter and seasonable mid-late week
All of the rain should be out of the area by midnight Tuesday
night/Wednesday morning. High pressure will build in at the sfc. We
see a couple of short waves try to clip the area, but they look like
they will stay just far enough north to not affect the area. The sfc
ridge will funnel dry air in from the NE through Friday. A weak
short wave approaches on Saturday, but it will not have much of any
moisture to work with. There could be maybe a weak shower on
Saturday, but for the most part the area should stay dry. Highs will
start out in the 50s on Wednesday, and warm to the 70s by Fri/Sat.
with return flow starting to develop.
&&
.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 214 AM EDT Mon May 18 2026
There are two main aviation concerns today, the first being the
chance of thunderstorms and the second being gusty south winds. As
for the chance of thunderstorms, a line of weakening showers/storms
is located off to the west over Wisconsin and Iowa at 06z. These
showers/storms will continue to slowly move our direction and will
begin to move into the area after 13z. We expect a weakening line
of activity that should mainly be showers at that point. An uptick
in activity or a redevelopment will occur between 16z and 18z as
the activity move through Southwest Lower Michigan. A period of
more substantial showers and some strong storms will be possible
between 18z and 23z. After 23z, the activity should wind down
and/or move off to the east. Conditions will largely be VFR
outside of the short periods that the activity affects any one TAF
site.
As for the wind, shortly after daybreak or around 13z we expect
winds to ramp up out of the SSW from 190-210. Speeds through the
bulk of the day will be between 15-30 knots.
&&
.MARINE...
Issued at 142 PM EDT Sun May 17 2026
We are going to expand the current Small Craft Advisory further
south to our border with IWX at St. Joseph. Plan views of winds
indicate that the strongest and most consistent winds will remain
north of Holland. However, there is enough wind on and off south
of Holland to necessitate the SCA down there. Right now we have it
going through Monday evening at 8 pm, but it will likely need to
be extended at some point through the Tuesday frontal passage.
Once the winds come down after the frontal passage on Tuesday
afternoon, headlines will likely not be needed for the rest of the
week.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...Small Craft Advisory until 8 PM EDT this evening for LMZ846>849.
&&
$$
DISCUSSION...NJJ
AVIATION...Duke
MARINE...NJJ
NWS GRR Office Area Forecast Discussion
