434
FXUS63 KGRR 200520
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
120 AM EDT Sat Jul 20 2024

.KEY MESSAGES...

- Fair weather continues with patchy morning fog possible

- Low Precipitation Chances Early Next Week, Better Chances
  Midweek

&&

.DISCUSSION...
Issued at 323 PM EDT Fri Jul 19 2024


- Fair weather continues with patchy morning fog possible

 High pressure at the surface and through the mid levels will allow
fair weather to dominate the weather pattern through Saturday.
The forecast question overnight will be fog formation. Winds will
be light and there will be a fairly strong inversion overnight.
The question is whether there will be enough surface moisture and
cooling for fog to form. The surface will be dry enough to
preclude any widespread fog. However, there is enough moisture,
especially along and south of the I 94 corridor to allow for
patchy fog overnight and through the early morning hours Saturday
morning. Any fog will lift and dissipate by mid morning.

 An upper level trough extending across southern Canada
and through the upper Great Lakes will drive an associated upper
level low through Minnesota tomorrow. This weak trough will trek
a boundary into Lower Michigan tomorrow afternoon. While there is
some mid level moisture associated with this boundary, dry stable
air over southern Michigan will keep any clouds and precipitation
further north and allow for the fair weather to continue into
Sunday.


- Low Precipitation Chances Early Next Week, Better Chances Midweek

The first half of the long-term period will be dominated by large
scale cyclonic flow from persistent troughing across the eastern
United States. This is a favored pattern for diurnally driven
scattered showers and thunderstorms Sunday and Monday afternoons,
mainly across the northern 2/3 of the CWA just south of a stalled
front. Slightly better low-level warm air advection and low-level
moisture bring the scattered thunderstorm chances areawide Tuesday
afternoon/evening. Favored areas for initiation each day will be
wherever low-level convergence is enhanced such as off of the lake
breeze. Synoptically, with weak flow aloft, deep layer shear is
poor. This supports convection of mainly a pulsey nature occuring.

Better synoptic forcing in the form of a reinforcing mid-level wave
arrives for Wednesday, with strong confidence in this feature across
model solutions. The associated developing surface low crosses into
West Michigan bringing the best chance for showers and
thunderstorms. This brings our best chance of precipitation for the
week Wednesday afternoon and evening. Monitoring will be needed as
the approaching wave brings a slightly better mid-level jet. The
associated ~30 knots of shear and 1000+ J/kg CAPE shown in some
solutions could indicate potential organized convection. Showers and
storms wind down Thursday and end by Friday as the mid-level low and
surface low pull away from southern Lower Michigan.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 120 AM EDT Sat Jul 20 2024

VFR conditions expected to continue through Saturday night. Only
exception would be for shallow ground fog bringing local MVFR and
perhaps IFR conditions between 08Z and 12Z at JXN...and the odds
of that are low.

&&

.MARINE...
Issued at 323 PM EDT Fri Jul 19 2024

Lighter winds will continue through Saturday and marine hazards
are not expected for the next few days. However, the strong
northerly flow from Thursday allowed for upwelling to occur and
portions of Lake Michigan`s beaches water temperature will be
cooler ranging from the upper 40s to low 60s.

&&

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

&&

$$

DISCUSSION...Ceru/Thomas
AVIATION...Ostuno
MARINE...Ceru