751
FXUS63 KGRR 170510
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
110 AM EDT Mon Jun 17 2024

.KEY MESSAGES...

- Thunderstorms Tonight

- Hot, humid with occasional thunder this week

&&

.DISCUSSION...
Issued at 305 PM EDT Sun Jun 16 2024

- Thunderstorms Tonight

The showers and storms across the central and northern zones will
move east this afternoon and should be moving east and out of the
forecast area this evening. Then we watch an MCV moving through
northern Illinois and southern Lake Michigan into our southwest
zones with the potential to bring locally heavy rain, hail and
high winds overnight across the southern half of the forecast
area. SPC marginal risk covers this threat area.

- Hot, humid with occasional thunder this week

The MCV propagates east and out of the forecast area by Monday
morning but is expected to leave behind an outflow boundary across
the southern forecast area that could focus some convection Monday
afternoon. The HREF has apparently picked up on this idea and now
has 70 to 80 percent probabilities of 0.1 QPF in this area on
Monday afternoon. We painted an area of higher POPs there but kept
them in the 25 to 35 percent range given lack of confidence in
the specifics.

The Heat Watch was not changed and it still appears that this
could be a long duration event where the cumulative effect of high
daytime and night time temperatures could necessitate a warning
being issued even without warning criteria being met on any one
day. There remains uncertainty on extent of convection on Tuesday
afternoon, but the the biggest uncertainty remains on Thursday
and Friday as a cold front or convective outflow could modify
temperatures across the northern half of the forecast area.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 110 AM EDT Mon Jun 17 2024

Lingering showers and thunderstorms at our southeast terminals
at the moment will gradually end during the next few hours.
Primarily VFR conditions are then expected at the terminals
overnight but some patchy MVFR fog will develop toward daybreak.
Any patchy fog will burn off by mid morning with VFR conditions
expected for the rest of the day.

Isolated showers and thunderstorms are possible in the afternoon
and evening but there is not enough potential or confidence in
timing to warrant mention in the terminal forecasts at this time.

&&

.MARINE...
Issued at 305 PM EDT Sun Jun 16 2024

No changes to the SCA or CFW. Current forecast on track with
southerly winds driving some higher waves from Grand Haven north
with structural and longwave currents making swimming dangerous.

Winds and waves could be locally higher in thunderstorms this
evening south of Muskegon.

Winds and waves will decrease slightly on Monday as the sfc
pressure gradient slackens a little, but the night shift can
evaluate this and determine if small craft and swim conditions
will improve enough for the SCA and CFW to expire at 2 am or have
to be extended.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Beach Hazards Statement until 2 AM EDT early this morning for
     MIZ037-043-050-056.
     Air Quality Alert until midnight EDT tonight for MIZ037-043-050-
     056-064-071.
     Excessive Heat Watch from noon EDT today through Friday evening
     for MIZ043>046-050>052-056>059-064>067-071>074.
MARINE...Small Craft Advisory until 2 AM EDT early this morning for
     LMZ847>849.

&&

$$

DISCUSSION...Ostuno
AVIATION...Laurens
MARINE...Ostuno