962
FXUS63 KGRR 271136
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
736 AM EDT Fri Jun 27 2025

.KEY MESSAGES...

- Hot, Humid, and Thunderstorms Today

- Drier Over the Weekend

- Chances for Showers and Storms Return Next Week

&&

.DISCUSSION...
Issued at 326 AM EDT Fri Jun 27 2025

- Hot, Humid, and Thunderstorms Today

Our current line of showers and thunderstorms is expected to exit
east of the area by daybreak, meanwhile behind the line isolated
showers and storms are possible. Additionally showers over Lake
Michigan and Wisconsin associated with outflow boundaries and
positive vorticity advection ahead of the 500mb trough axis will
move in early this morning providing another focus for showers and
storms. Not expecting any severe storms with this mornings
convection, but could see some strong to severe storms this
afternoon mainly along and south of a Kalamazoo to Lansing line.
This is due to the slow moving front allowing instability around
2000 to 3000 J/kg to build ahead of it. We`ll be on the backside
of the 500mb jet of 30-40 knots providing some upper level
divergence. Sounding profiles support the potential for strong
winds, especially the farther east you go. This is also supported
by various machine learning guidance and the updated SPC outlook.
Thunderstorms look to exit the area by the early evening with dry
conditions expected overnight.

Precipitable water values still remain high toward 2 inches. As
seen over the past few days 1 to 2 inch per hour rainfall rates
are possible and could cause some minor flooding in urban areas
and known trouble spots.

Lastly it will be another hot and steamy day until the front moves
through, especially along and south of that Kalamazoo to Lansing
line. Heat indices will be in the 90s for much of the area with
some spots approaching 100. With only isolated spots possibly
hitting 100 due to thunderstorms and cloud cover, held off on any
Heat Advisory.

- Drier Over the Weekend

Drier conditions are expected over the weekend, with a cooler day
for Saturday with highs in the 70s to low 80s and heat indices
matching air temperatures. Temperatures warm up once more for
Sunday with highs in the upper 80s to low 90s ahead of our next
chance for rain. Heat indices in the mid to upper 90s are
expected.

- Chances for Showers and Storms Return Next Week

Our next chance for rain and thunderstorms arrives Sunday night
into Monday as a shortwave trough moves through. Additional
shortwave troughs move through each night through Wednesday night.
Most of the long range ensemble members are dry though after rain
exits the area Monday with the drier air in place. Therefore kept
the NBM POPs of less that 20 percent, but will need to monitor if
moisture improves within these shortwaves. After Monday,
temperatures look a bit more comfortable with highs in the 80s and
lows in the 50s and 60s.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 736 AM EDT Fri Jun 27 2025

Isolated showers and storms will be possible northwest of GRR this
morning before chances expand southeast after 15Z. Better chances
hold off until 18Z where pop up showers and storms are expected
mainly along and south of an AZO to LAN line. Storms may become
more scattered along the front before it exits the area by 00Z.
Storms this afternoon could be strong to severe with gusty winds
and hail. Any thunderstorm will be capable of heavy rainfall with
rates of 1 to 2 inches per hour.

VFR conditions are expected tonight into Saturday morning with
winds from the west to northwest.

&&

.MARINE...
Issued at 326 AM EDT Fri Jun 27 2025

Southerly winds are expected with isolated showers and storms
possible this morning and early afternoon. Winds become more west
to northwesterly late this afternoon and overnight behind a cold
front. High pressure Saturday will keep winds light and variable
before shifting to the south Saturday night into Sunday as the
high shifts east. Southwest winds build during the day Sunday and
may approach Small Craft Advisory conditions during the afternoon.
Waves however look to remain in the 1 to 3 foot range into next
week.

&&

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

&&

$$

DISCUSSION...RAH
AVIATION...RAH
MARINE...RAH