448
FXUS63 KGRR 192333
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
733 PM EDT Sun May 19 2024

.KEY MESSAGES...

- Marginal Risk for severe storms Monday afternoon/evening

- Strong to Severe Storms Possible Later Tuesday into Wednesday

- Dry Weather Thursday into early Saturday

&&

.DISCUSSION...
Issued at 335 PM EDT Sun May 19 2024

- Marginal Risk for severe storms Monday afternoon/evening

A shortwave trough is minoring out as it moves across the central
Great Lakes on Monday with warm advection/isentropic ascent aiding
the development of scattered rain showers and storms Monday
morning into afternoon. Although instability is present with CAPE
spiking up to around 1000 j/kg by afternoon, deep layer shear is
limited to about 20 to 25 knots. The marginal risk for severe
storms lingers into the evening as the leading edge of an MCS or
MCV is coming across Lake Michigan and reaching western zones by
00Z as indicated by model guidance, including the Hi Res ARW and
FV3.

This line or cluster of storms is pushing east and weakening by
late Monday evening as instability decreases and the severe threat
should be over by midnight. The main threat with these storms
appears to be isolated downbursts in bowing line segments, but a
tornado threat cannot be ruled out if local wind profiles are
modified by the evolution of an MCV.

- Strong to Severe Storms Possible Later Tuesday into Wednesday

By Tuesday the presence of a strong low pressure system over the
north-central United States plants lower Michigan firmly in the warm
sector with dewpoints well into the 60s. This allows plenty of
instability to build with MUCAPE values climbing to near and north
of 2000 J/kg with near to above 30 knots of shear by Tuesday
afternoon. Two rounds of storms are possible Tuesday. First, some
scattered storms are possible Tuesday afternoon as the low-level jet
moves in and warm front lifts north. Then more widespread showers
and storms Tuesday night into Wednesday morning as the subsequent
cold front moves through the CWA.

Guidance is still split on when the cold front arrives and how fast
it moves through. The ECMWF solution is more aggressive and has the
frontal boundary clearing the area by 18z while the GFS and NAM
support a slower front. The slower the front crosses the state, the
more destabilization can occur ahead of the frontal boundary
Wednesday for the Southeastern CWA. As the low and mid-level jets
overspread the region, shear ahead of the front climbs over 40 knots
Wednesday bringing potential severe weather concerns focused on the
southeastern portions of the area as CAPE values remain elevated if
the slower front materializes.

Overall, some uncertainty remains in the timing of any thunderstorms
which affects the finer details of severe weather potential.
However, later Tuesday into Wednesday the parameter space will be
favorable for the chance of strong to severe storms. This will need
to be monitored and details fine-tuned over the next few days.
Regardless, Tuesday will be warm and a bit muggy with temps well
into the 80s. Highs Wednesday will generally be in the 70s but if
the front slows some areas may reach the 80s.

- Dry Weather Thursday into early Saturday

Predominantly zonal mid-level flow and surface ridging is expected
after the front exits later Wednesday. This combined with a lack of
deep moisture will support not only dry conditions but even
potentially a few sunny days Thursday and Friday with highs in the
70s. The next chance of rain and increasing clouds will be Saturday
as a cold frontal boundary and shortwave approach West Michigan.
Though as expected at this range, differences in timing and position
exist keeping some uncertainty as to exact timing and coverage of
showers.

&&

.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
Issued at 733 PM EDT Sun May 19 2024

Much of this forecast period will be quiet with little to no
impact and VFR conditions. The exception to this will be a 2-4
hour period mid-morning to early afternoon when a batch of showers
and storms will move through.

We only have high clouds around 25k ft agl moving in this evening
from the tops of storms well to our west. These clouds will
continue to move in and thicken overnight. Drier low levels will
keep any rain and fog from forming.

The models have been in fairly good agreement showing a batch of
left over showers and storms coming in from the west beginning
around mid morning. It looks like the northern terminals will be
favored, with less of a chance for the southern terminals.
Confidence is high enough for expected wording at the I-96
terminals, and VCTS at the I-94 terminals. This will also be the
case for MVFR-IFR conditions.

Once these move out, most of, if not all of the rest of the
forecast period will be mainly dry with some clearing. Another
batch of storms will approach Monday evening, but likely just
after the end of this period.

&&

.MARINE...
Issued at 335 PM EDT Sun May 19 2024

Winds and waves should remain below Small Craft Advisory the next
few days although locally higher winds and waves are possible in
thunderstorms on Monday afternoon through Tuesday night.

&&

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

&&

$$

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