709
FXUS63 KGRR 181048
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
648 AM EDT Mon May 18 2026
.KEY MESSAGES...
- Slight Risk for Severe Storms Today
- Slight Risk for Severe Storms on Tuesday
- Drier and cooler mid to late week
&&
.DISCUSSION...
Issued at 400 AM EDT Mon May 18 2026
- Slight Risk for Severe Storms Today
The storm prediction center has placed Southwest Lower Michigan in
a slight risk for severe weather today. Clouds and showers will
try to press in from the west this morning which will decrease
somewhat how much we can destabilize. 500mb flow will be
weakening as we move through the day as well which is another
negative factor with regard to severe weather chances. What we
are watching though is the chance that the current activity
redevelops or regenerates over our area after about noon (this is
seen in the HREF). We feel that between roughly 100pm and 700pm
there is chance for severe weather, especially south and east of a
line from Whitehall to Clare (so the bulk of the area). An item
of note in the HREF is the 850mb low level jet ramps up during the
afternoon to 40-45 knots. The LLJ increase is seen most for areas
near and southeast of GRR including AZO, LAN and JXN. These areas
stand the best chance at some damaging winds this afternoon and
evening. The Nadocast machine learning website also sees wind as
our biggest threat today over our southeast half of the forecast
area. There is a chance for some scattered storms tonight, but
nothing that looks widespread.
- Slight Risk for Severe Storms on Tuesday
Another slight risk for severe storms is in place for Tuesday over
the southeast CWA. The setup is similar in that decaying showers
and storms will move in during the morning with a threat of
redevelopment over our area in the afternoon. Tomorrow`s threat
though looks more confined to the southeast CWA, essentially a
smaller threat area including AZO, LAN and JXN. Today we have some
threat outside of those areas, but tomorrow (Tuesday) the best
chances may very much be confined to those areas. Deep layer shear
on Monday is 25-35 knots and Tuesday that increases to 30-40
knots. So some storm organization is possible especially with
Tuesday`s threat. Again though, the morning clouds and showers may
dampen our threat a bit.
- Drier and cooler mid to late week
The cold front will sweep through the forecast area Tuesday
evening. Much drier air will invade from the north with PWAT
values plummeting from 1.7 inches Tuesday morning which is off the
chart for this time of year to less than 0.5 inches on Wednesday.
It will be noticeably cooler with highs in the 60s Wednesday and
Thursday. Wednesday night we are likely looking at frost across
Central Lower Michigan.
Another systems looks to bring some rain out towards Friday, but
the models have had difficulty coming to a consensus. The trend
though looks to be towards rain on Friday.
&&
.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 647 AM EDT Mon May 18 2026
Very little change in thinking from overnight. We are expecting a
broken line of showers and thunderstorms to move into Western
Lower Michigan between 14z and 17z. These will largely be in a
weak state. Re-intensification will take place around 17z however
with a line of showers and storms then expected to push eastward
through the TAF sites. Have VCTS in the TAFs now, but we expect
at least scattered activity to affect the TAF sites between 17z
and 23z. All sites will largely stay VFR today outside of some
brief reductions in visibility and ceiling associated with a storm
affecting any one TAF site.
Winds will ramp up considerably in the next hour or two (or by 13z
to 14z), with SSW winds from 190-210 running at 15-30 knots much
of the day.
&&
.MARINE...
Issued at 400 AM EDT Mon May 18 2026
We have extended the Small Craft Advisory both in time and areal
extent. The SCA now runs through Tuesday for all zone. The
southern two zones, south of Holland, begin tonight. Strong
southerly winds will continue both today and Tuesday as we remain
east of the cold front the bulk of that time. South winds of 15 to
25 knots look common with waves of 3 to 6 feet. The SCA may need
to be extended into Tuesday night for a period of stronger
northwest winds behind the cold frontal passage.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...Small Craft Advisory from 2 AM to 8 PM EDT Tuesday for LMZ844-
845.
Small Craft Advisory until 8 PM EDT Tuesday for LMZ846>849.
&&
$$
DISCUSSION...Duke
AVIATION...Duke
MARINE...Duke
NWS GRR Office Area Forecast Discussion
