-- Discussion containing changed information from previous version are highlighted. --
657
FXUS63 KGRR 241645
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1245 PM EDT Fri May 24 2024

.KEY MESSAGES...

- Potential for Severe Storms This Evening/Tonight

- Potential for Severe Storms on Sunday

- Turning A Bit Cooler with Showers Monday and Tuesday

&&

.DISCUSSION...
Issued at 349 AM EDT Fri May 24 2024

- Potential for Severe Storms This Evening/Tonight

Quiet weather starts our day as we look to this evening for
thunderstorm activity. A mid-level trough curls northwards from
the northern Plains while a corresponding surface low over the
Dakotas also pivots northeastwards into southeastern
Manitoba/western Ontario. Thunderstorm activity will occur along a
trailing cold front as it sweeps through the Upper Mississippi
Valley and into Lower Michigan.

Timing still seems to favor the 8pm to 2am window with storms
entering the decaying phase as diurnal instability declines. An
additional instability element to consider will be decaying shower
activity/convection ahead of the main cold front convection and
whether that activity will put a damper on available instability as
the cold front arrives. The 0z HREF keeps MUCAPE sub 1000J/kg across
most of lower Michigan with values up to 1000-1500J/kg nosing just
into Berrien/Van Buren/Cass Counties.

Storms will originate in Iowa and move east into Wisconsin and
northern Illinois before arriving in lower Michigan late this
evening. Wind gusts will be the primary hazard as storms develop
in a linear mode with some bowing segments possible. While the SPC
Outlook keeps the Slight Risk across far southwest Michigan,
severe wind gusts will be possible up much of the lakeshore.
Several hi-res models key in on the frictionless lake dynamics and
advertise strong gusts as far north as Ludington as the front
crosses Lake Michigan and arrives at the West Michigan lakeshore.

- Potential for Severe Storms on Sunday

A deepening low pressure system is forecast to be moving into the
Great Lakes from the southwest on Sunday. The low reaches the low
990s mb by Sunday evening as it moves into the Northern Great Lakes.
A warm front will be lifting north through Lower Michigan during the
day with a cold front poised to move in during the evening. The low
looks to be driven by a convectively generated lead vort within a
broader trough moving our way from the Plains. Given the depth of
the low, its not surprising wind fields are strong. 850mb LLJ
strength is 40-50 knots and increasing into the evening. The mid
level jet at 500mb is 50-60 knots. Deep layer shear is strong.
Instability is forecast to be moderate to high as higher dew point
air surges in with the warm front. At this point the SPC Day 3
outlook for Sunday is south of our area, but can see this creeping
north into Lower Michigan with time as model differences are ironed
out and confidence increases. All severe hazards could be in play on
Sunday across the forecast area.

- Turning A Bit Cooler with Showers Monday and Tuesday

An upper trough gradually develops overhead as we head into the
holiday and Tuesday. Showers will occur on both days but it will
not be a total washout. Shortwaves will be working through the flow
over the Great Lakes, so its hard to envision totally dry forecast
periods Monday through Tuesday night. Upper ridging gradually works
in for Wednesday and Thursday along with a surface high. Dry weather
is expected Wednesday and Thursday. Temperatures also cool from the
70s on Sunday...back into the 60s for Monday through Wednesday.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
-- Changed Discussion --
Issued at 1245 PM EDT Fri May 24 2024

VFR at present with just high cirrus out ahead of a line of
showers and storms over Wisconsin. Given little to no instability,
the line will dissipate before arrival with maybe a dying shower
clipping MKG this afternoon. Redevelopment of storms is expected
this evening near and after 00z. Have refined the period of VCTS,
favoring the HRRR which seems to have the most realistic handling
of the ongoing storms. Certainty in timing and coverage is still
too low to go with TEMPO at this time. Showers will be ongoing
through 11z behind the line. Cigs fall to sub-fuel alternate MVFR
for a from approximately 08z-13z due to the rain given moisture
before lifting as daytime heating mixes them out. from the south
to southwest around 10 knots are expected through the TAF window
becoming westerly late tonight. However, locally higher gusts are
possible in any storms mainly for MKG, GRR, and AZO.
-- End Changed Discussion --


&&

.MARINE...
Issued at 349 AM EDT Fri May 24 2024

Marine conditons stay quiet through today, then waves build Saturday
morning with increasing westerly winds. Waves peak around 3 to 4
feet Saturday mid-morning then quickly decline. Winds and waves
build early Monday morning through Tuesday at which time conditons
will be hazardous to Small Craft and waves and currents will be
dangerous to swimmers.

&&

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

&&

$$

DISCUSSION...Duke/Thielke
AVIATION...Thomas
MARINE...Thielke