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245
FXUS63 KGRR 050155
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
955 PM EDT Tue Jun 4 2024

.KEY MESSAGES...

- Dry tonight, showers/storms Wednesday

- Cooler and unsettled through the weekend

&&

.UPDATE...
-- Changed Discussion --
Issued at 955 PM EDT Tue Jun 4 2024

Latest RAP shows a surge of higher PWATs over 1.5" arriving
overnight from southwest to northeast, with a 30-35 kt low level
jet setting up over Lk MI and the lakeshore counties. Also the H5
shortwave over wrn IL will be arriving after 06Z and will help
break down the upper ridge which is currently in place. Rain
chances will be ramping up accordingly, although the
higher/likely probabilities through sunrise should be limited to
areas near and west of Highway 131. Not much sfc based
instability to work with but incoming H8 LI/s near -2C will
support a late-night thunder risk. Temps holding up in the 70s
for much of the night thanks to clouds and southerly flow, with
early morning lows generally in the upper 60s.
-- End Changed Discussion --

&&

.DISCUSSION...
Issued at 322 PM EDT Tue Jun 4 2024

- Dry tonight, showers/storms Wednesday

The 18z surface analysis showed a cold front near the Red River of
the North and extending southward through western MN into
northeast NE. This cold front will be a key to our weather
Wednesday.

Radar shows developing storms over northeast Wisconsin, but they
are moving north and won`t affect southwest Lower tonight.
However, CAMs suggest that more scattered convection will develop
over portions of IL and southern WI later this evening and slowly
move in our direction as the aforementioned cold front makes
steady progress east. As instability wanes after midnight, these
storms to the west should diminish somewhat, but probably not
totally. Thus, we may be looking at some morning convection across
the western cwa Wednesday morning. Instability is somewhat
lacking during the morning and so we may see more showers than
storms, and the storms that do develop will likely be non-severe.
That could change by afternoon.

SPC has placed the southeast cwa in a Marginal risk for severe
storms Wednesday. This is mainly southeast of a Lansing to Battle
Creek line with the focus on the afternoon. There is still
uncertainty with this system and really hinges on how much the
atmosphere can recover after morning showers/storms. If lingering
clouds can thin a bit, then we`ll see more heating which will push
SBCAPE higher. Bulk shear around 35 knots will support cell
organization. The Nam3km, FV3, HRRR all show variations of
afternoon redevelopment with the Nam3km the most aggressive. Wind
would be the main threat with hail secondary.

The cold front will push through by 00z Thursday, ending the
severe threat, but it may not end the thunderstorm threat. Earlier
runs of the HRRR hinted at a secondary line moving in conjunction
with a strong upper low moving over the Great Lakes, so we`ll keep
chc PoPs in the grids for this.

- Cooler and unsettled through the weekend

A nice shot of cooler air will flow into the cwa behind the cold
front. H8 temps fall from 16c to 4c by Thursday afternoon. Friday
through Sunday will see highs in the 60s...a nice refresher from
today`s highs in the mid to upper 80s. The upper low will be
camped out over the Great Lakes through Sunday before moving east
Monday, only to be followed by another upper trough Tuesday. We`ll
keep low chance PoPs in the forecast for this but by no means will
it be raining all the time.

A slow warming trend will develop by next Monday with highs in
the mid to upper 70s by next Tuesday.

&&

.AVIATION /00Z TAFS THROUGH 00Z THURSDAY/...
Issued at 859 PM EDT Tue Jun 4 2024

VFR continues to dominate the weather pattern through the first
half of the overnight period. A line of weakening showers and
storms moves NE across the Lake. This line of convection will have
little, if any affect on TAF sites.
 However there were be several lines of showers and storms that
will move through region beginning tomorrow morning through the
afternoon. Expect lowering cigs after 10Z with the main threat
between 15Z to 19Z.
 Periods of TSRA will be possible but have only VCTS at TAF sites
due to uncertainty.

&&

.MARINE...
Issued at 322 PM EDT Tue Jun 4 2024

A cold front will move across the lake Wednesday. Gusty west winds
behind the front will likely create waves that will necessitate a
Small Craft Advisory and Beach Hazards Statement Wednesday night
and Thursday. Additional headlines may be needed later in the week
too as cooler air flows over the lake creating hazardous waves.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...None.

&&

$$

UPDATE...Meade
DISCUSSION...04/CAS
AVIATION...Ceru
MARINE...04