934
FXUS63 KGRR 060735
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
335 AM EDT Mon May 6 2024

.KEY MESSAGES...

- Strong to possibly severe storms possible on Tuesday

- Rain on Thursday and Saturday

&&

.DISCUSSION...
Issued at 331 AM EDT Mon May 6 2024

- Strong to possibly severe storms possible on Tuesday

We are looking at a quiet period for the first 24-30 hours of the
forecast for the area. High pressure at the surface is nearly
overhead this morning, and the supporting upper ridge is west of the
area. We are seeing a veil of high clouds lifting north over the
area from a system that is centered south of the area near the Ohio
River Valley. Dry air at the lower levels will keep our dry forecast
going for today. The flow becoming a little more SE by later today
along with the building heights will warm temperatures a few degrees
over yesterday. The warmest temps will be found near the Lake
Michigan shoreline with the offshore flow.

Monday night and most of Tuesday morning will remain dry before rain
chances increase quickly Tuesday afternoon from the SW. A piece of
energy from the Severe weather outbreak expected over the Central
Plains this afternoon and evening will be lifting toward the area.
This part of the scenario looks rather benign as the wave and low
level jet accompanying it will be weakening. It will hold together
enough to bring a weakening band of showers and embedded thunder
through the area centered around the early to mid-afternoon time
frame. No severe weather is expected with this.

What does bear watching though is potentially a second round of
storms with a trend of increasingly favorable instability and shear
for late Tuesday and maybe evening into early Tuesday night. In the
wake of the initial showers and storms, we see a secondary short
wave approach the area from the WSW around the parent low complex.
Even though we see rain early that will temper sfc temperatures,
instability builds to over 1,000 J/kg. This is the result of the
short wave and associated colder mid level temps moving over the
moist low levels with dew points in the 60s.

Mid level winds will be increasing also, with 500 mb winds
increasing to around 60 knots or so. Given the aforementioned
instability, forcing arriving with the short wave, and deep layer
shear increasing to over 50 knots, we could be looking at some
strong to severe storms developing. Large hail looks to be the
biggest threat with mid level lapse rates around 7.0C/km, and some
of the storms likely to be rotating in the mid levels with the
strong shear, and microbursts will be possible too. An isolated
tornado can not be ruled out either at the leading edge of these
storms with some backed wind flow, and some initially decent low
level shear with the low level jet just starting to move away.

- Rain on Thursday and Saturday

A couple shortwave troughs will result in chances for showers
peaking Thursday and Saturday. Confidence is above average with good
model agreement and ensemble support.

An area of mid-level frontogenesis north of a low pressure center
tracking across the Ohio Valley will result in rain moving in late
Wednesday night and continuing through Thursday afternoon. Northerly
flow on the back side of the low will advect in a cool Canadian
airmass. We will have to watch for frost potential if skies clear
out Thursday night.

Shortwave ridging should continue the fair weather for Friday into
Friday night but clouds will be moving in after midnight as the next
shortwave trough approaches, with rain moving back in for Saturday.
There could be some diurnal enhancement of the showers Saturday
along with some thunder given steep lapse rates as the upper trough
axis moves through.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 128 AM EDT Mon May 6 2024

VFR conditions will prevail through tonight. The exception will
be an area of MVFR conditions in thin layer of stratus clouds
at JXN early this morning but those should break up by 12Z.

Winds will be light and variable tonight and east or southeast
around 10 knots on Monday.

&&

.MARINE...
Issued at 335 AM EDT Mon May 6 2024

No marine issues expected through at least most of tonight. Winds do
start to increase aloft tonight, but they will be warm winds over
the colder lake waters, and offshore in nature. This usually keeps
winds below thresholds. We may need some headlines for Tuesday
afternoon into Wednesday with the system moving through, and cooler
weather surging in on the backside.

&&

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

&&

$$

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