591
FXUS63 KGRR 211148
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
748 AM EDT Fri Jun 21 2024

.KEY MESSAGES...

- Chance of thunder today, better chance Saturday and Saturday
  night

- Drying out Sunday; Pleasant Monday

- Strong storms possible Tuesday/Tuesday night

- Dry and cooler Wednesday through Friday

&&

.DISCUSSION...
Issued at 338 AM EDT Fri Jun 21 2024

- Chance of thunder today, better chance Saturday and Saturday
  night

The frontal boundary that triggered storms Thursday is now south
of the cwa and pretty nondescript. In it`s wake, we`ll have a
little less instability today, however, precipitable water values
will remain north of 1.75 inches. We probably won`t see much
precipitation this morning. However during the afternoon, the
frontal boundary to the south will begin to move back north and
there may be a 3-6 hr window beginning around 20z in which we see
some convective development over the southeast cwa. There will
likely be a decent lake shadow with any convective development due
to persistent west winds. Gusty winds and torrential downpours are
the main threat with any storms that develop today.

Highs around 90 today and dewpoints in the lower 70s will send
heat indices into the mid 90s again; no changes to the Heat
Advisory.

After a dry night tonight, chances for storms will increase
Saturday from north to south. Showers/storms will likely be
ongoing Saturday morning over northern Lower along the warm
frontal boundary. Once the the attendant low moves east, the cold
front will begin to drop south during the mid to late afternoon.
Showers and thunderstorms will likely develop along the front and
will mostly affect the northern cwa Saturday afternoon. SPC has
placed the entire cwa in a Marginal Risk for severe storms
Saturday/Saturday night. Heavy rain will also be a threat with
PWATs closing in on 2.5 inches.

Will maintain high probabilities (80-90 percent) for showers and
thunderstorms on Saturday night as lead shortwave and sfc cold front
pass through the region. Severe weather and heavy rain threat will
linger in the evening then wane overnight with the passage of the
cold front and departure of the 2"+ PWAT air. The frontal passage
will also bring an end to the persistent heat and humidity.

- Drying out Sunday; Pleasant Monday

On Sunday the primary nrn stream H5 shortwave drops into the nrn
GrtLks Rgn and a cooler/less humid air mass filters in on the heels
of northwest winds. Morning clouds and lingering showers/drizzle
giving way to decreasing clouds in the afternoon. Monday still looks
like a pleasant day as the sfc ridge builds in.

- Strong storms possible Tuesday/Tuesday night

Tuesday could be an active weather day as the warm/humid air makes a
quick return from the southwest and temps push toward 90 again. Fast
northwesterly flow aloft could send an MCS or two our way from
Wisconsin, thriving off cape values possibly in excess of 3000 J/KG.

- Dry and cooler Wednesday through Friday

The push of warmer air is short-lived as the passage of a cold front
on Tuesday night/early Wednesday ushers in another installment
cooler/drier air. Northerly winds on Thursday ahead of an advancing
sfc high sends dew points down into the 40s/50s. Lows in the 50s and
highs in the 70s expected later in the week as high pressure settles
overhead by 12Z Friday.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 748 AM EDT Fri Jun 21 2024

Areas of IFR/LIFR due to fog and stratus early this morning will
mix out or lift toward VFR levels by afternoon. Scattered
thunderstorms developing again this afternoon, although generally
favoring the area east of GRR and AZO so have only included a
mention of thunder at LAN and JXN. The strongest cells may contain
torrential rain, gusty winds and hail so if they directly impact
those terminals there could be brief IFR or lower conditions and
possibly a wind gust over 30 kts. Convection ending by 00Z this
evening then mainly VFR anticipated tonight.


&&

.MARINE...
Issued at 338 AM EDT Fri Jun 21 2024

A weak pressure gradient today will result in low wind and waves.
An approaching cold front Saturday will likely cause wind and
waves to increase and a Small Craft Advisory/Beach Hazards
Statement may be needed by Saturday afternoon.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Heat Advisory until 8 PM EDT Saturday for MIZ056-057-064>067-
     071>074.
MARINE...None.

&&

$$

DISCUSSION...Meade/04
AVIATION...Meade
MARINE...04