635
FXUS63 KGRR 231935
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
335 PM EDT Thu May 23 2024

.KEY MESSAGES...

- Severe Weather Potential Friday evening

- Not A Washout But Wet At Times This Holiday Weekend

&&

.DISCUSSION...
Issued at 335 PM EDT Thu May 23 2024

- Severe Weather Potential Friday evening

Quiet weather tonight through Friday afternoon then we look for a
line of thunderstorms advancing eastward across Lake Michigan into
the western zones during the evening and weakening as it moves
across Lower Michigan.

The large scale synoptic pattern looks somewhat similar to Tuesday
night with shortwave ridging across the central Great Lakes tomorrow
being followed by height falls in the evening as an upper low moves
from the Dakotas into Canada. An occluded front extends southward
from the primary sfc low with a triple point low forming in
southern Minnesota or Wisconsin. Organized convection is expected
in this area Friday morning then tracks east and reaches Lake
Michigan during the evening.

The timing is a bit slower with the most recent hi res model runs
and the consensus is that the storms will reach western Lower
Michigan closer to 03Z. Instability is diminishing at that time
and deep layer lift is off to the northwest of Lower Michigan, so
this could be another case of the storms dissipating before they
get in here. On the other hand the 12Z GFS trended stronger with
deep layer shear and has the storms arriving by 00Z. At this point
we will continue messaging the potential while noting the
uncertainty.

- Not A Washout But Wet At Times This Holiday Weekend

The Memorial Day weekend does not look to be a washout by any means,
however several rounds of showers and thunderstorms are possible
from Saturday through Monday.

Rain Saturday will be mainly concentrated in the morning hours as we
see a cold front exit during the morning hours. High pressure and
dry air then bring mostly sunny skies for the rest of the day. Highs
will be in the low to mid 70s Dry conditions then occur into the
first part of Sunday before out next round of precipitation.

Our next round of precipitation arrives Sunday afternoon as a warm
front lifts north across the area aided in forcing by a mid-level
wave. Confidence is high in rainfall but the degree of instability
present is still uncertain. One thing of note in 12z guidance is it
has has trended a bit more north in the placement of the low and
warm front and a bit more aggressive with the low level jet. This
trend suggests that some surface based instability may make it into
at least the I94 corridor (probability of CAPE greater than 500 J/kg
for KAZO is currently 30-50 percent). While chances for stronger
storms presently look to remain south of us, monitoring for possible
continuance of this northward trend is needed given the strong
dynamics in play.

Shower chances continue into Monday (though the occluding low
passing overhead cuts off instability) with the chance for diurnal
enhancement due to the upper-level cold pool being overhead. The
synoptic setup favors more of wrap-around showers with cold-pool
enhancement so Monday doesn`t look to be a washout at present as
showers remain scattered. The cold-air advection also suggests a
breezy Monday which is supported in the ensembles (ECMWF Probability
of gusts above 25 mph is over 90 percent). This pattern continues
into Tuesday and possibly even Wednesday with additional showers
possible in the north-west flow pattern as the upper-level cold pool
meanders to our northeast. Highs in the 70s Sunday fall into the 60s
for the first part of next work week.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1243 PM EDT Thu May 23 2024

Very high confidence in VFR through the TAF period. At present,
FEW to SCT cirrus are crossing the state and will exit by late
evening. A few cumulus are possible but given how dry we are it`s
unlikely to see more than SCT at the terminals around 5-6kft.
Skies clear out overnight and remain so after 12z until cirrus
approach the western terminals (MKG/GRR/AZO) just before the end
of the TAF window. The other item of note is winds. West-Southwest
winds around 10 knots this afternoon fall below 5 knots tonight
with a general shift to the east to southeast as a boundary
slides through. Tomorrow morning through the end of the TAF
window expect generally southeasterly winds of 5-10 knots.

&&

.MARINE...
Issued at 335 PM EDT Thu May 23 2024

Winds and waves will remain relatively light through Sunday
although there could be stronger gusts Friday evening as a line of
thunderstorms moves across Lake Michigan. Winds and waves will
increase on Monday and a Small Craft Advisory could be needed.

&&

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

&&

$$

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