465
FXUS63 KGRR 191520
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1120 AM EDT Wed Jun 19 2024

.KEY MESSAGES...

- Hot/humid today with a chance of storms

- Not as hot Thursday

- Sct`d storms Friday through Sunday; highest chance Saturday night

- Hot and Breezy Saturday

- Dry and more comfortable Sunday through Tuesday

&&

.UPDATE...
Issued at 1054 AM EDT Wed Jun 19 2024

The 12z KDTX sounding showed thicker CAPE just below the -20 deg
C level and DCAPE values around 750 J/kg. Already we had one cell
just south of Jackson County that some indications of hail. With
PWAT`s running over 1.8 inches near that cell, and a relatively
slow movement, it`s not surprising that locally over an inch of
rain fell with it. Looking at the afternoon, we will continue to
destabilize. Bulk effective shear values were elevated(30kts) over
southeast parts of the CWA. DCAPE was highest along the I-96
corridor with values topping 1000 J/kg. High res models like the
HRRR and NAM 3km have been showing convection developing over
south to southeast parts of Lower MI this afternoon with outflows
lifting northward through the late afternoon hours. Some of these
may collide leading to additional convective development. Given
the favorable DCAPE and mid level CAPE near the -20 deg C level,
gusty winds and hail may accompany any stronger convection.
Locally heavy rainfall will be possible as well.

Heat index values were nearing 90 degrees already. Most locations
in the headline area should end up in the 93 to 98 degree range
this afternoon.


&&

.DISCUSSION...
Issued at 322 AM EDT Wed Jun 19 2024

- Hot/humid today with a chance of storms

Another hot and humid day is expected. As of 3am, it`s still 82 at
Holland. Needless to say, temperatures won`t have to rise much to
reach the 90s today. As dewpoints close in on 70 this afternoon,
heat indices will rise into the mid to upper 90s. CAMs show a
seasonably robust short wave lifting north today from the MO
bootheel. As it arrives this afternoon, we`ll see isolated
convective develop within a weakly sheared environment that will
see 1500 j/kg SBCAPE and PWATs near 2 inches. A marginal risk of
severe storms exists for the southeast cwa mainly for the
potential of gusty winds.

- Not as hot Thursday

GFS and ECMWF show a weak cold front dropping south tonight and
northeast winds developing that will continue Thursday. It`s
likely temperatures will be a little cooler Thursday with highs
around 80 near US-10 to around 90 near I-94. If the cooler trend
continues in the models, we may be able to drop the Heat Advisory.
The ECMWF also showed weak low pressure riding east along the
frontal boundary Thursday resulting in showers/storms over the
eastern cwa. Given the humid environment in place, any storms that
develop will be capable of producing heavy rain.

- Sct`d storms Friday through Sunday; highest chance Saturday night

The center of the upper high continues to drift southwest over the
weekend, from the TN Valley on Friday to Texas by Sunday. Shortwaves
riding around the periphery of the upper high combined with weak
surface convergence and peaking afternoon/evening instability will
continue to support a daily risk for showers and storms through the
weekend.

The highest chance of storms comes on Saturday night when a cold
front presses southeast through the region ahead of an approaching
nrn stream shortwave. Deep layer shear values will be ramping up by
then as the influence of the upper ridge slips away so we may be
looking at a round of severe weather as that system comes through.

- Hot and Breezy Saturday

Ahead of that cold front/shortwave a surge of even warmer air
arrives for Saturday with guidance temps as suggesting readings as
high as 95 well inland from Lk MI. Southwest winds may gust over 30
mph.

- Dry and more comfortable Sunday through Tuesday

It is that nrn stream shortwave which ushers in less humid and not
as hot weather for a few days early next week with lows in the lower
to mid 60s and highs in the lower 80s. Confidence in a dry Monday is
fairly high as high pressure passes overhead, before low pops creep
back in with returning warm air by midweek.

&&

.AVIATION /12Z TAFS THROUGH 12Z THURSDAY/...
Issued at 748 AM EDT Wed Jun 19 2024

BKN-OVC cigs above 12,000 ft this morning giving way to SCT-BKN
cumulus/CBs around 4000 ft later today. Widely scattered tstms
developing this afternoon and continuing into early evening.
Local/brief IFR conditions possible should a storm with heavy
rainfall pass over a terminal, with the main risk of storms being
south and east of GRR between roughly 20Z and 02Z. Southwest winds
10 to 20 kts (higher at MKG), diminishing later in the day and
becmg lgt and vrbl this evening. Some MVFR cigs expected to
arrive at MKG and GRR after 08-09Z tonight.

&&

.MARINE...
Issued at 322 AM EDT Wed Jun 19 2024

Surface and buoy obs indicate winds are gusting over 25 knots and
waves currently are in the 3-4 foot range; we`ll continue with the
Small Craft Advisory and Beach Hazards Statement today. Wind will
decrease as the day progresses and the pressure gradient slackens.

After today, we`ll see several days where wind and waves will not
be hazardous to boaters or beach goers.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Beach Hazards Statement until 4 PM EDT this afternoon for MIZ037-
     043-050.
     Heat Advisory until 8 PM EDT Friday for MIZ043>046-050>052-
     056>059-064>067-071>074.
     Air Quality Alert until midnight EDT tonight for MIZ050-056-057-
     064-071.
MARINE...Small Craft Advisory until 4 PM EDT this afternoon for
     LMZ847>849.

&&

$$

UPDATE...MJS
DISCUSSION...Meade/TJT
AVIATION...Meade
MARINE...04