692
FXUS63 KGRR 181719
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
119 PM EDT Wed Sep 18 2024

.KEY MESSAGES...

- Continued hot and dry

- Chances for showers Fri and Sun-Tue

&&

.DISCUSSION...
Issued at 312 AM EDT Wed Sep 18 2024

- Continued hot and dry.

Today will be another in a long string of above normal
temperatures and dry weather.

Latest surface analysis shows sfc dewpoints near 60 over far
southeast Lower...roughly 8-10 degrees higher than over the cwa.
Short range models show the ESE wind flow pushing those higher
dewpoints westward today. HREF cloud progs point toward some CU
developing east of US-127 late morning/early afternoon. However,
afternoon mixing will draw down drier air from aloft and tend to
dissipate the cu throughout the afternoon; we`ll still be looking
at a mostly sunny sky.

The upper Rex block will remain intact through Thursday. Tonight
will be a repeat of clear skies and patchy overnight fog, followed
by another mostly sunny day Thursday.

- Chances for showers Fri and Sun-Tue

The slow breakdown of the blocking pattern late this week into next
should spell an end to the persistent dry and sunny weather, with 80-
degree days becoming less favored after Sunday. The upper levels in
the northern stream will tend to transition to more progressive
Rossby waves as a stronger North Pacific jet streak moves in next
week. The interaction of the northern stream with the southern
stream over the southern US, which will tend to be more stationary
and prone to blocking, complicates the large-scale evolution of the
pattern over the CONUS next week. The details on when specifically
rain might occur next week are quite disparate in the ensembles.

There is however some clustering in the ensembles for a minor chance
of showers on Friday, followed by a somewhat better chance Sunday-
Tuesday. There are even some plausible solutions for soaking rain
amounts over 1 inch by Tuesday, though this is not yet the most
likely outcome. Friday may have weak elevated instability to support
thunder chances, especially in northern areas closer to the
influence of the weak shortwave trough. The Sun-Tue timeframe will
depend on the extent that a northern stream trough will dig into the
Dakotas and upper Midwest, followed by the potential for a compact
upper-level low in the southern stream to migrate out of the
southwest US.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 114 PM EDT Wed Sep 18 2024

A similar setup for fog to impact the terminals appears in place
for early Thursday morning. Model guidance (GFS LAMP, HRRR
soundings) does suggest fog is most likely at AZO, BTL, LAN, and
JXN especially in the 09z-13z time frame. Like today and
yesterday, much of this may take until 14z-15z to totally mix out
and dissipate. The HRRR soundings show less in the way of
saturation at the surface than what occurred today, so maybe the
1/4 mile visibilities will be less commonplace.

&&

.MARINE...
Issued at 312 AM EDT Wed Sep 18 2024

Southeast winds 5 to 15 knots will result in 1 to 2 foot waves
over the next couple of days. Dry weather is expected through
Thursday.

&&

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

&&

$$

DISCUSSION...04/CAS
AVIATION...Hoving
MARINE...04