921
FXUS63 KGRR 202349
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
749 PM EDT Mon May 20 2024

.KEY MESSAGES...

- Marginal Risk of Severe Weather This Evening

- Slight Risk of Severe Weather Tuesday Night

- Chance of Storms Wednesday

&&

.DISCUSSION...
Issued at 305 PM EDT Mon May 20 2024

- Marginal Risk of Severe Weather This Evening

Multiple lines of convection from Lake Michigan to southern
Wisconsin and northern Illinois this afternoon will be moving
into Lower Michigan this evening. Latest radar trends are showing
a weakening of the storms over Lake Michigan but these storms
could strengthen again as they move back over land with 500 to
1000 J/kg of MUCAPE to work with. The main threat is isolated wind
damage with the strongest convection. The severe threat will
diminish with loss of sfc heating this evening. The showers will
be exiting the eastern zones around midnight.

- Slight Risk of Severe Weather Tuesday Night

There should be a lull in the convection as the first shortwave
trough minors out/moves east and is replaced by flat ridging
before heights fall again late Tuesday afternoon and evening as
the next shortwave trough axis swings through along with
increasing shear profiles and deep lift. Scattered convection in
the afternoon will give way to increasing POPs as organized
convection along and ahead of the cold front pushes in from the
west.

Primary threat will again be scattered wind damage with stronger
updrafts or bowing line segments, but model soundings from the GFS
and NAM show possible QLCS tornado threat with favorable low
level helicity as near sfc winds veer strongly with height.

- Chance of Storms Wednesday

The front bringing the chance for severe weather Tuesday night
continues to drive south and east during the day on Wednesday. The
GFS/NAM have trended towards the ECMWF suggesting the front clears
our southeast CWA in the vicinity of 18z Wednesday. Given how early
the front clears the area, the potential for convective
redevelopment is uncertain. There are signals for the potential of
showers and storms to develop south and east of Grand Rapids, mainly
down towards Jackson, Wednesday afternoon and evening aided by a
passing vorticity maximum.. If any development can happen on the
warm side of the front, a strong to severe storm cannot be ruled out
given 40-45 knots of deep layer shear hence the current marginal
risk for severe storms. Rain chances end early Thursday.

Dry weather is expected Thursday into Friday as surface ridging
aided by zonal flow at 500mb ridging by Friday and little to no
deep layer moisture. The lack of moisture also keeps plenty of
sunshine in the forecast with highs well into the 70s Thursday and
Friday.

An lead shortwave ahead of a parent trough approaches early Saturday
increasing clouds and rain chances, further increasing Saturday and
into the day on Sunday as a weakening surface low sends a front
through the area with renewed cyclogenesis over the central Great
Lakes. Exact timing and placement of important features, as expected
over 5 days out, is still uncertain but the broader signal across
guidance is generally similar. So, while timing and extent of any
precipitation is uncertain, the chance does exist for rain during
the memorial day weekend. This means the NBM 30-40 percent PoPs are
appropriate for the end of the week.

&&

.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 743 PM EDT Mon May 20 2024

As expected, a line of thunderstorms is moving across Western
Lower Michigan. Cig/Vis aren`t dropping too much as these storms
go through, with conditions mostly staying low VFR, but winds do
become briefly gusty and erratic. This line of storms moves east
over the next several hours and is expected to be fully past
Lansing and Jackson by 4-5z tonight. An area of low clouds and fog
are still expected to develop for the 2nd half of the night and
continue through sunrise. LIFR conditions still look likely, and
recent model trends suggest AZO/BTL/LAN could get in on the
cig/vis reductions now as well, though they should be on the edge
of the worst conditions. Regardless, conditions improve rapidly
after sunset tomorrow as strong mixing wipes out the clouds and
sun takes back over.


&&

.MARINE...
Issued at 305 PM EDT Mon May 20 2024

Offshore winds and waves below 3 feet through Tuesday although
there could be some locally strong winds and choppy waves in the
vicinity of thunderstorms this evening and again Tuesday night.

Winds will pick up Tuesday night and Wednesday with waves building
to 6 to 8 feet Wednesday morning.

&&

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

&&

$$

DISCUSSION...Ostuno/Thomas
AVIATION...AMD
MARINE...Ostuno