014
FXUS63 KGRR 171404
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
1004 AM EDT Sun May 17 2026
.KEY MESSAGES...
- Scattered showers and storms today with a warm front
- Threat for severe storms on Monday
- Additional severe storms possible Tuesday
- Quieter weather mid to late week
&&
.UPDATE...
Issued at 1004 AM EDT Sun May 17 2026
We have ramped up the messaging this morning about the severe
weather potential for this afternoon. This comes after
coordination with SPC to bump up the Marginal risk to a Slight
risk north of I-96 for this afternoon into this evening. In
addition, a tornado or two is possible.
Stalled out front sits just north of the I-96 corridor this
morning as of 10 am per sfc obs. South of the front winds are from
the south with temps in the 70s and dew points in the 60s. North
of the front, winds have an easterly component with temps in the
60s and dew points in the 50s. This front will be trying to lift
north a bit as the deep flow becomes more from the SW.
This all has been expected, but we have an extra ingredient
entering the picture that could ramp this threat up a bit. There
is a well defined MCV exiting Iowa into Wisconsin and Northern
Illinois. This feature is expected to move over the northern
section of our area, and likely interact with the front.
Plenty of instability will be present near and south of the front,
with ML CAPEs up to around 1500, and MU CAPEs pushing 2500 J/kg.
The mid level flow and MCV coming in will help to ramp up the deep
layer shear to 40-50 knots near the front, tapering off to the
south. Add in good low level shear along the front with the
strongly backed flow near and just north of the warm front, SRHs
over 200 and 400-500 at 0-1km and 0-3km respectively, lead to a
fairly large and favorably looped hodograph toward the M-20
corridor.
Hail is probably the biggest threat with the potential of some
rotating storms leading to hail with mid level lapse rates over
7.0C/km. Wind is also a threat with the strong deep layer shear,
especially near and just of the boundary where the storms will be
sfc based.
We will have to see how this interaction occurs and plays out, as
convection always has a degree of uncertainty. This has the
potential to become a bit active over our northern counties from
mid-afternoon to mid-evening, and has definitely garnered our
attention.
&&
.DISCUSSION...
Issued at 409 AM EDT Sun May 17 2026
- Scattered showers and storms today with a warm front
A warm front will lift northward through Southwest Lower Michigan
tonight bring in higher dew point air and associated instability.
By evening mid 60s dew points should be in place over much of the
area. MUCAPE values should surge into the 1500 to 2500 j/kg range.
Plenty of instability for storms with the trigger being the warm
front. CAMs are not overly bullish though on coverage which makes
sense given today`s convection will be located within an upper
ridge position overhead. Feel a few storms are possible this
morning with a slight increase in coverage this afternoon given
daytime heating. Severe weather is not out of the question today
and SPC rightly has us in a marginal threat. Deep layer shear is
actually quite strong due to a convectively induced mid level jet
that move in from the west today from strong storms in the Central
Plains this past evening. The stronger shear, moderate instability
and a warm front nearby make all severe weather hazards possible
today. Showers and storms should lift to the north/end this
evening as the warm front lifts northward and we lose daytime
heating.
- Threat for severe storms on Monday
The active weather pattern that begins today will continue into
Monday. Another round of showers and strong to severe storms are
possible on Monday. The SPC has Southwest Lower Michigan in a
slight risk for severe weather. A strong southwesterly low level
jet of 35-40 knots will be in place with another convectively
induced mid level jet moving through as well. The threat on monday
looks to be centered in the midday through afternoon hours as this
is when a MCV will likely be working through the areas from
overnight convection in the plains. MUCAPE values should increase
to around 2000 j/kg with deep layer shear on the order of 30 to 40
knots. Wind and hail look to be the main threats on Monday in the
open warm sector of the system.
- Additional severe storms possible Tuesday
Another round of storms and possible severe weather will occur as
a strong cold front sweeps from west to east through the area on
Tuesday. 30 to 40 knots of deep layer shear looks to be in place
once again with in excess of 2000 j/kg of MUCAPE ahead of the cold
front. Wind and hail will once again be threats during the
afternoon.
- Quieter weather mid to late week
Cooler and drier weather is expected overall mid to late week with
high pressure building in from the north. 850mb temperatures
actually dive towards zero C Wednesday from a peak around +18C
Monday night. Wednesday and Thursday certainly look dry, but there
is some model disparity out on Friday with the GFS and the ECMWF
at odds in regard to the pattern. The GFS has a low in the area
while the ECWMF has ridging.
&&
.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 649 AM EDT Sun May 17 2026
Largely VFR weather is expected the next 24 hours at the TAF sites
across Southwest Lower Michigan. There are two main concerns, the
first being some early morning fog today near I-94. The I-94 TAF
sites have seen visibilities bounce around this morning with
current values around 1 to 2 miles. We expect this fog to lift
quickly this morning and to be gone by 15z. The second concern is
the threat of thunderstorms, especially this afternoon and early
evening. Have covered the threat at this point with VCTS wording
as we are not expecting widespread storms. The storms this
afternoon and evening will be capable of severe weather with large
hail and damaging threats at least. The greatest likelihood
however for severe weather today will be north of the TAF sites
for the most part across Central Lower Michigan. Aviation
interests should monitor conditions closely as to where these
storms develop this afternoon.
&&
.MARINE...
Issued at 409 AM EDT Sun May 17 2026
Strong southerly flow will develop tonight and continue into the
early portion of the work week. For now we will cover the first 24
hours of the wind and issue a Small Craft Advisory from this
evening through Monday for areas north of Holland. The wind will
continue into Monday night and Tuesday and expand to the south of
Holland as well with time. So, as we move forward the SCA will
need to be expanded in time and also in area (to the south). Waves
will reach the 3 to 6 foot range north of Holland on Monday.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...Small Craft Advisory from 11 PM this evening to 8 PM EDT Monday
for LMZ846>849.
&&
$$
UPDATE...NJJ
DISCUSSION...Duke
AVIATION...Duke
MARINE...Duke
NWS GRR Office Area Forecast Discussion
