889
FXUS63 KGRR 082323
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
723 PM EDT Tue Jul 8 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 /00Z TAFS THROUGH 00Z THURSDAY/...
Issued at 722 PM EDT Tue Jul 8 2025

Scattered showers and isolated thunderstorms are forecast to
develop after 02-03z and continue through the overnight hours.
Have prevailing showers for AZO/BTL/JXN where better coverage will
be and VCSH for the northern terminals where it is less certain.
Cannot rule out breif periods of MVFR conditions in heavier
showers but confidence is too low for TAF inclusion.

Coverage of showers and storms will increase beginning late
Wednesday morning through late afternoon as a cold front crosses
the area. Best chance for any showers and storms is at BTL/LAN/JXN
so have included a PROB30 for thunder there with lower chances to
the west. If a thunderstorm directly impacts a terminal
restrictions to cigs/visbys and gusty winds are possible.
Southwest winds tonight will become northwest behind the front
Wednesday afternoon.

&&

.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...Thomas
MARINE...Ceru