441
FXUS63 KGRR 090554
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
154 AM EDT Wed Jul 9 2025

.KEY MESSAGES...

- Showers and storms possible Through Wednesday

- Fair weather through the end of work week

- More widespread, organized system on Saturday

&&

.DISCUSSION...
Issued at 330 PM EDT Tue Jul 8 2025

- Showers and storms possible Through Wednesday

 Large upper level low over central canada has an upper level
trough extending through the upper midwest with a shortwave trough
extending through Indiana to Missouri. As that trough moves
through overnight it could have enough instability and mid level
moisture to spark some late evening/overnight convection across
lower Michigan. Some of the CAMS do show potentially 500 to 1000
J/kg of CAPE moving into Lower Michigan. This along with a nub of
effective bulk shear into northern Lower could allow storms to
linger and strengthen early Wednesday morning.
 As that trough continues its eastward progression expect mid
level instability along with level low pressure to pull up some
gulf moisture and deepen, which should further aid afternoon
convection. This should bring an increase of CAPE and while SPC
has the area only outlooked for general thunder there is some
potential for some storms to become strong, especially along and
east of the US 127 corridor.

- Fair weather through the end of work week

 Weak high pressure will move over the area Thursday into Friday.
This will keep any showers at bay through the end of the week.
Temperatures should rise as warm air advects into the region.
Highs could get into the low 90s by Friday afternoon.


- More widespread, organized system on Saturday

Mid to long range models remain consistent on a more widespread
rain event Saturday. High pressure will be situated over the
Southern US, and another High over southern California.
 An upper level wave will move Eastward from the west coast,
through Southern Canada. As that trough moves east, it will
continue to deepens,extending into the upper Mid west by Saturday
afternoon. That trough should be advecting moisture between the
before mentioned high`s from the Gulf of America, along with warm
air. This warm, moist advection should bring 1.75 PWATS of
moisture, according to the NAEFS. While not highly anomalous, it
should be enough for widespread precipitation through Saturday.
That through should move quickly to the east with drier, zonal
flow in its wake.

&&

.AVIATION /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 154 AM EDT Wed Jul 9 2025

We are looking at a complicated forecast period through the first
18 hours or so before conditions improve for all of the terminals.

We have scattered showers and storms over most of the southern
third of the forecast area, or all of the terminals except KMKG,
and near KGRR. These scattered showers and storms are forecast to
persist through the first 4-6 hours of the forecast, and could
drop conditions down to MVFR or even IFR under the heaviest cells.
They should tend to diminish temporarily after 10-12z.

We will see additional showers and storms develop then this
afternoon as the front passes through. The front will first pass
through KMKG early, like 09-12z and have some showers and lower
clouds possibly with it, with light winds and the abundant
moisture in place.

We will see additional showers form and some storms as we see
heating of the day boost this activity. Coverage should be enough
for all of the sites except KMKG, to go with a tempo TSRA group
for a few hours this afternoon. It appears most of this activity
should move out of all of the sites by 21-22z this afternoon. Some
bkn VFR clouds may linger into the evening hours, but will clear
out before the end of this forecast period.



&&

.MARINE...
Issued at 315 PM EDT Tue Jul 8 2025

As the trough exits tomorrow afternoon, northerly flow should
increase behind the front. There remains the potential for a
stronger gradient forming along the lakeshore. As the winds shift
from the northwest to the north, it could bring winds upwards of
15 to 25 kts and waves upwards of 2 to 5 feet, especially north of
Grand Haven. There remains some questions of timing and strength.
So have held off on headlines for now but another set of
marine/swim headlines remain possible.

&&

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

&&

$$

DISCUSSION...Ceru
AVIATION...NJJ
MARINE...Ceru