983
FXUS63 KGRR 212350
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
750 PM EDT Fri Jun 21 2024

.KEY MESSAGES...

- Scattered Storms This Evening

- Organized Convection with heavy rain Saturday into Saturday
  night

- Drying Out and Cooler Sunday and Monday

- Strong storms still possible Tuesday/Tuesday night

- Pleasant stretch expected Wednesday into the weekend

&&

.DISCUSSION...
Issued at 331 PM EDT Fri Jun 21 2024

- Scattered Storms This Evening

ML CAPE values were up to 1500 J/kg around the region and low
level convergence was maximized over northeast zones. Effective
bulk shear values were highest over northern zones from near
Ludington to Harrison. PWAT values were near 2 inches. Thus
isolated/scattered storms will continue to develop inland through
the remainder of the evening with locally heavy rain. With the
effective bulk shear elevated north, this is downstream of the
cell now near Green Bay. We will need to monitor that feature as
the environment downstream of it is quite unstable.

- Organized Convection with heavy rain Saturday into Saturday
  night

A low level jet forms upstream in IA overnight and then noses into
northern parts of the CWA Saturday morning. The warm front will
be up in this area as well. Thus showers and thunderstorms will
likely expand over the northern zones during the day. The warm
front will likely remain nearly stationary and that could support
training echoes. With PWAT values up around 2 inches and forecast
soundings suggestive of efficient rain, rainfall could be
excessive in some areas. It`s still uncertain the exact location
of where the front will stall out and where the convection will
train, but that something to monitor closely in coming forecasts.

An impressive warm sector sets up over the CWA Saturday afternoon.
With strengthening wind fields, the risk for severe weather will
increase. If any convection gets going near or just south of the
warm front around our northern zones, the forecast deep layer
shear is supportive for organized convection. Then during the
evening, a stronger mid to upper level wave and associated cold
front will be tracking in from the west. Instability will be
sufficient for stronger storms. That in combination with the
stronger deep layer shear could lead to a line of storms with
stronger wind gusts. The main window for this to happen is after
00z Sunday.



- Drying Out and Cooler Sunday and Monday

Lingering light showers Sunday morning should give way to clearer
and slightly cooler conditions by Sunday afternoon. Dry conditions
persist through Monday into early Tuesday. Temperatures should back
off into the lower 80s both days. Some breezy conditions on Sunday
but generally in the 15 to 25 mph range.

- Strong storms still possible Tuesday/Tuesday night

Continuing to keep on eye on the set up of hot/humid air building
from the south with MCSs tracking through the Great Lakes from the
northwest. This is our target for any significant weather in the
upcoming week and will have to continue to be watched for severe
weather potential.

- Pleasant stretch expected Wednesday into the weekend

Once the last of the MCS exits by early Wednesday a pleasant stretch
of weather should move into lower Michigan. Wednesday through Friday
should be really nice with highs in the upper 70s to lower 80s with
much less humidity than we`ve seen in recent days.  Could see some
heat return next weekend through much of next week but currently not
looking as oppressive as what was experienced this past week.

&&

.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 750 PM EDT Fri Jun 21 2024

We are seeing a lull in the shower and storm activity across the
area with the last of the showers/storms moving out of the area.
VFR conditions have returned to all areas. Additional showers and
storms are expected later tonight, but are likely to stay north of
the terminals. Winds will go lighter overnight, but will stay up
aloft. This should prevent fog from forming, but it is something
we will keep an eye on.

More widespread showers and a few storms will arrive toward KMKG
around 12z Saturday, and move east through the morning. We have
gone with showers with MVFR conditions, and a prob30 for storms
and IFR conditions at KGRR and KMKG. Elsewhere, it looks like the
showers/storms will be much less in coverage, and have handled
this with a VCSH for now.

It does look like that one more widespread line of showers and
storms will move into the area with the front. This will come
after 00z Sunday however.

&&

.MARINE...
Issued at 331 PM EDT Fri Jun 21 2024

A low level jet will arrive later tonight and persist into
Saturday evening. This will likely lead to increasing winds and
waves. Model projections suggest we will remain under criteria for
small craft and beach hazards through much of Saturday. During
Saturday evening there could be enough increase in the winds and
waves to warrant some headlines. With several rounds of convection
expected over the next 48 hours, they could impact the wind setup.
For now we will hold off on a any headline issuance`s given the
uncertainty.

&&

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

&&

$$

DISCUSSION...MJS/Maczko
AVIATION...NJJ
MARINE...MJS