841
FXUS63 KGRR 170533
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
133 AM EDT Fri May 17 2024

.KEY MESSAGES...

- Scattered showers and storms tonight/early Friday

- Dry and Mild Weekend

- Active Weather to Start the Work-Week

&&

.UPDATE...
Issued at 955 PM EDT Thu May 16 2024

Evening showers and storms are now diminishing as diurnal
instability declines. Any regeneration/redevelopment overnight
remains most likely in the northern zones (US-10 corridor) due to
proximity to the shortwave and associated lift moving through
Wisconsin and into the U.P. However, last few hi-res model runs
have backed off a bit on thunderstorm coverage after midnight
tonight, so it`s possible it could end up being a pretty calm
night overall.

&&

.DISCUSSION...
Issued at 328 PM EDT Thu May 16 2024

- Scattered showers and storms tonight/early Friday

A shortwave and accompanying sfc frontal boundary track slowly east
through the region tonight and Friday morning, but are generally
weakening as they do so. Instability isn`t the greatest either
especially since these features come through mostly during the
diurnal minimum.

Initially this evening scattered showers and storms will be
associated with the incoming warm front and higher dew points,
then overnight will be linked more to the nearing WI shortwave and
cold/occluded front. HREF guidance suggests best coverage of rain
will be during the overnight period especially east of Hwy 131.

Will carry some lingering low (20-30 pct) pops Friday mainly
near/east of U.S. 127 and near/south of I-94 since the sfc front
stalls out and there is still some lingering sfc instability
(SBCapes 500-1000 J/KG). Otherwise decreasing clouds and a warm
Friday expected with highs in the upper 70s. May have to consider
a risk of patchy fog Friday night in light wind/clear sky regime.

- Dry and Mild Weekend

High pressure moves into the region resulting in dry weather this
weekend. An 850mb thermal ridge peaking at +12 to +14C moves
overhead Saturday and Sunday resulting in high temperatures into the
80s with plenty of sunshine.

- Active Weather to Start the Work-Week

A deepening longwave trough will eject out of the Rockies at the
start of the work week sending a series of shortwaves through the
Great Lakes Region. This will result in an active weather pattern
through the first half of the week with showers and storms possible.

The first round of storms will move through Monday evening as a
front sweeps through the area. Instability looks sufficient ahead of
the front to support some showers and storms Monday evening, but the
better chance appears to be Tuesday afternoon and evening. As a more
potent shortwave moves overhead, a surface low will track through WI
into the UP while a trailing cold front sweeps through the state.
Instability will build throughout the day Tuesday ahead of the front
while a 40 to 50 knot Low Level Jet noses into Michigan during the
evening. Model guidance has yet to come into good agreement
therefore confidence remains low, but Tuesday may be a day to
monitor the the potential for strong to severe storms in the area.

Temperatures will drop closer to normal (normal highs are around 70)
Wednesday and Thursday following the passage of the front.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 127 AM EDT Fri May 17 2024

VFR conditions were noted across the terminals, but that will
likely change as the overnight progresses. Short range models show
a fairly strong signal for IFR cigs/vsbys to develop after 08z
especially at MKG which may see some fog develop over the lake and
advect inland. Current dewpoint depressions are in the 2-3 degree
range and recent spotty rains may help to speed the development of
some stratus.

Conditions will improve during the late morning.

&&

.MARINE...
Issued at 955 PM EDT Thu May 16 2024

A few showers and storms are possible overnight mainly north of
Grand Haven, but this is looking less likely than it did earlier.
Meanwhile, what does look likely is the development of fog
overnight. By daybreak, we could be looking at dense fog
conditions that persist through late morning. Otherwise, light
west winds continue.

&&

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

&&

$$

UPDATE...AMD
DISCUSSION...Meade/Thielke
AVIATION...04
MARINE...AMD