555
FXUS63 KGRR 061913
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
313 PM EDT Mon May 6 2024

.KEY MESSAGES...

- Potential for strong/severe storms Tuesday

- Wet and Cool Weather for the end of the week


&&

.DISCUSSION...
Issued at 308 PM EDT Mon May 6 2024

- Potential for strong/severe storms Tuesday

Severe storms are just developing over the Plains in response to
strong dynamics being produced by low pressure over the northern
Plains along a warm/occluded frontal band. These storms...in
weakening mode...will move east tonight and move toward Lower MI
Tuesday morning. These storms will be weakening as they move
across the cwa Tuesday morning due to drier air and limited
instability.

Once the initial showers/storms move across by late morning,
we`ll likely see a lull of a couple of hours and with more storm
redevelopment during the mid afternoon. CAPE values increase
dramatically behind the frontal boundary and will be helped out
by any clearing that we see. An approaching strong short wave
that`s ejected out of the Plains upper low will support convective
redevelopment. Dewpoints surge into the lower 60s behind the
front. Strong shear in the 55 kt range coupled with 1k+ j/kg
SBCAPE, 6.5-7 C/km mid level lapse rates 40kt LLJ and a 75kt mid
level jet will support organization. In this case, the strongest
dynamics will remain south of the cwa, but will be strong enough
to produce a wind and hail threat from roughly 3pm-8pm. SPC has
highlighted a Slight Risk for severe storms generally south of
I-96 with a Marginal Risk for most of the rest of the cwa. Any
lingering showers/storms should be out of the cwa by 06z
Wednesday.

- Wet and Cool Weather for the end of the week

A positive tilted mid level wave will be tracking through the Great
Lakes region later Wednesday and into Thursday.  PWATs climb as this
feature tracks through topping an inch in southern parts of the CWA.
This is a good setup for period of steady rain, which will also act
to keep the temperatures down.  The models do vary considerably
with the location and amounts of rain.  The GFS has been steady in
showing a swath of heavier rain for  Muskegon River basin, while the
ECMWF and GEM are aiming the precipitation further south and trending
further south.

Another mid level wave comes down from the Canadian Prairies on
Friday night.  This wave will bring down another surge of cool air
and there could even be some lake effect rain showers with this
second wave. While qpf is projected to be light, given the
enhancement of the moisture from Lake MI, we will nudge up the POPs
for Friday night into Saturday to account for this. With 850 mb
temps struggling to top 0 deg C, the daytime temperatures are likely
to stay at least several degrees below normal for both Friday and
Saturday.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 130 PM EDT Mon May 6 2024

The atmosphere will remain relatively dry into the start of
Tuesday so VFR conditions are predicted. An overall east to
southeast flow will prevail as an area of high pressure retreats
northeastward into southern Ontario and into Quebec. A band of
showers and embedded thunderstorms will likely be moving into the
southwest TAF sites of KMKG, KAZO and KBTL by noon so we featured
conditions trending downward at that time. Thunderstorms were not
included as there is some uncertainty of whether there will still
be thunderstorms as the band of precipitation moves in near the
end of the forecast period.

&&

.MARINE...
Issued at 308 PM EDT Mon May 6 2024

Southeast wind gusts will increase to around 20 knots tonight
which may touch on advisory criteria for a few hours Tuesday
morning, but given the offshore flow and the short duration, we`ll
hold off on a headline for now.

Thunderstorms are possible Tuesday morning and again Tuesday
afternoon, which the afternoon storms being potentially strong to
severe.

&&

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

&&

$$

DISCUSSION...MJS/04
AVIATION...MJS
MARINE...04