809
FXUS63 KGRR 220605
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
205 AM EDT Sat Jun 22 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

&&

.UPDATE...
Issued at 1038 PM EDT Fri Jun 21 2024

A stationary boundary stretches from southern portions of the
Thumb west across Southwest Lower Michigan. The front is located
along the Wisconsin/Illinois line into Northern Iowa. This front
is forecast to move northward tonight across our area in response
to an upper shortwave (and its associated surface low) moving out
of the Central Rockies and into the Plains. The 850mb low level
jet begins to increase in strength overnight across Southwest
Lower Michigan. We expect continued development of scattered
showers and storms tonight across Central Lower Michigan on the
nose of the low level jet. A more concentrated area of showers and
storms will likely be pushing across Lake Michigan near and just
before 12z per the morning run of the HREF. This activity will be
associated with a much stronger low level jet that will exist
tonight in the Plains. Rainfall amounts will be held in check
tonight by the scattered nature of the precipitation. A much
heavier round of rainfall is expected Saturday afternoon into
Saturday night ahead of the low and the associated cold front.
Another warm night is expected with lows in the upper 60s to
around 70.

&&

.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 /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 205 AM EDT Sat Jun 22 2024

The cluster of showers and storms currently over srn WI and nrn IL
extrapolates northeast into MKG around 11-12Z and should last on
and off through much of Saturday morning. These may impact GRR as
well although probably to a lesser extent than MKG. Ocnl MVFR/IFR
possible as these storms pass through. After the morning
convection it looks like the MKG/GRR terminals may dry out and go
predominantly VFR for this afternoon before more showers and
storms return after 00Z this evening.

Otherwise VFR weather prevailing all day for the terminals south
and east of GRR with the bulk of the rain and tstms remaining
off to the north over central and nrn Lwr MI. The potential for
showers and storms does not really ramp up across this area until
after about 02-03Z tonight. Winds increasing to 12-22 kts out of
the southwest by Noon today.

&&

.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...Flood Watch from noon EDT today through late tonight for
     MIZ037>040-043>046-050>052.
     Heat Advisory until 8 PM EDT this evening for MIZ056-057-064>067-
     071>074.
MARINE...None.

&&

$$

UPDATE...Duke
DISCUSSION...MJS/Maczko
AVIATION...Meade
MARINE...MJS