601
FXUS63 KGRR 091045
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
645 AM EDT Thu Jul 9 2026
.KEY MESSAGES...
- Scattered Showers and Storms Today
- Mostly Dry Weekend Favored and Heating Back Up
&&
.DISCUSSION...
Issued at 350 AM EDT Thu Jul 9 2026
- Scattered Showers and Storms Today
Scattered showers and thunderstorms remain the mode today. While
not as warm as yesterday, the humidity will be a little higher. A
weak cold front slowly arriving from the northwest, weak midlevel
shortwave troughing, and remnant vorticity maxima from yesterday
evening`s convection over the Upper Miss. River valley, should
serve to initiate shower and storm development. Initially elevated
convection is possible most anywhere later this morning, then
more surface-based storms would be favored east of US-131 during
the afternoon.
CAPE should be in the range of 750-1500 J/kg. Low-level wind
shear is expected to be weak, and deep layer shear of 20 kt is
also on the marginal side. With weak forcing and weak storm-
relative inflow, storm updrafts should be smaller-scale and less
likely to produce severe hail. By afternoon, the well mixed lower
levels and DCAPE around 600 J/kg would support locally gusty winds
under any of the more robust storm cells, with a marginal risk of
severe winds near and east of Battle Creek - Lansing. Rain today
is not guaranteed in any location. However, an isolated inch or
more of rain could fall in a couple spots.
Added patchy fog into the forecast for early Friday morning as
winds go calm and skies partially clear. Isolated showers or
storms may continue to percolate in mid/southern Lower Michigan
tonight into Friday.
- Mostly Dry Weekend Favored and Heating Back Up
Rising heights in the upper levels and a strengthening surface
high over Lower Michigan this weekend will favor a dry forecast.
There is about a 10 percent chance of a shower or storm popping up
on Sunday, better chances north.
As a 500 mb high (associated with a heat wave out west)
strengthens and migrates from the SW CONUS to the Dakotas this
weekend into Monday, a plume of 20-25 C air at 850 mb will advect
into Michigan from the west-northwest Monday-Tuesday. High
temperatures in the 90s away from Lake Michigan are well supported
by the ECE and GEPS. Dew points may be a little lower than with
last week`s heat wave, but a heat index in the mid to upper 90s is
favored. Mid to late week, the spread in solutions increases (and
confidence decreases), dependent on the relative strength and
position of the central CONUS high and the eastern Canadian
trough, but now a majority of ECE members and about 25 percent of
GEPS members (not to mention a few GEFS members) keep highs in the
90s through Friday.
&&
.AVIATION /12Z TAFS THROUGH 12Z FRIDAY/...
Issued at 645 AM EDT Thu Jul 9 2026
A few showers or an isolated thunderstorm cell ongoing this
morning. Expecting cloud bases mostly at or above 4,000 feet
today. The big caveat to the prevailing VFR will be scattered
showers and thunderstorms developing during the day and moving
east. Went with a pretty long duration window of prob30
thunderstorm as models offer a wide variety of solutions regarding
coverage and location of thunderstorms at a given time. Any
better-developed thunderstorm cells this afternoon, especially
east of GRR-AZO, will be capable of microbursts/LLWS and temporary
IFR visibility. Patchy fog may develop Friday morning around 08 to
12 Z.
&&
.MARINE...
Issued at 350 AM EDT Thu Jul 9 2026
Light winds and low waves expected over Lake Michigan today, with
wind direction variable depending on location. Can`t rule out an
isolated thunderstorm developing over the lake this morning.
Friday, north-northwest winds may build 2 to 4 foot waves and a
moderate swim risk by late afternoon. Swim risk is expected to be
low this weekend with a high pressure system over the area.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...None.
&&
$$
DISCUSSION...CAS
AVIATION...CAS
MARINE...CAS
NWS GRR Office Area Forecast Discussion
