645
FXUS63 KGRR 260121
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
921 PM EDT Sat May 25 2024

.KEY MESSAGES...

- Potential for Storms on Sunday

- Cool and unsettled weather Monday through Tuesday

- Dry and increasingly warmer late week; rain chances Saturday

&&

.UPDATE...
Issued at 919 PM EDT Sat May 25 2024

A pleasant evening is unfolding across southwest Lower MI. Skies
are mostly clear and dewpoints are in the 40s. No changes planned
to the going forecast. Temperatures will fall into the upper 40s
near US-10 and lower 50s elsewhere as high clouds begin to move in
from the west after midnight.

&&

.DISCUSSION...
Issued at 328 PM EDT Sat May 25 2024

- Potential for Storms on Sunday

We continue to track the arrival of the next round of
active/unsettled weather Sunday afternoon and Sunday evening.
Convection-allowing models over the last several runs continue to
bring a line of showers and storms through Lower Michigan late
tomorrow (Sunday) afternoon. This line will be oriented northwest
to southeast. The basic ingredients for thunderstorms will mostly
be in place: a shortwave trough moving through the southwesterly
flow near peak-heating, a warm front, eventually a surface cold
front, and even an 850 hPa low strengthening and moving through
the area to our north. The big question remains, though, whether
all these ingredients are able to come together at the right time
to produce any strong-to-severe storms in our area. We remain in
a marginal risk (Level 1 of 5) of severe storms from the Storm
Prediction center for Sunday.

The limiting factor continues to look like insufficient
instability (fuel for storms) able to work back into Lower
Michigan as the overall flow becomes more southerly during the day
Sunday. The window of time for the advection of unstable air is
limited in the current progressive pattern anyway, and with the
track of an associated surface low sticking with a more southern
solution (over the heart of Lower Michigan) this will keep our
time in the warm sector limited. The most likely place for
sufficient instability to develop for any severe threat remains in
the far south, along the I-94 corridor, but even that is far from
a sure bet, as the exact evolution of upstream convection today
and tomorrow morning will play a bit part in establishing outflow
boundaries for any additional MCS`s to follow.

The other dimension of Sunday`s storms will be a notable return of
humidity and elevated PWAT values approaching 1.5". With
widespread showers and storms expected, followed by a more showery
pattern heading into the start of the week, we could see
widespread 0.5" to 0.75" rain totals, with a few localized totals
upward of 1.5". This isn`t expect to result in any flooding, but
will keep small streams a bit elevated for this time of year, in
addition to ponding of water on roads during the heaviest
downpours.

- Cool and unsettled weather Monday through Tuesday

The system that will bring the rain to the area Sunday and Sunday
night will be absorbed into a much more broader low complex that
will extend from Hudson Bay through the Great Lakes. This complex
will get stuck over the region for a couple of days, and bring
periodic rain shower chances to the area Monday through Tuesday as
short waves rotate through the area. It does look like there will be
a small chance of thunder during the daylight hours each day with
diurnal instability present. The period will not be a complete
washout with some peeks of sunshine and dry periods.

Temperatures will also cool down to a little below average under
this upper low complex as one would expect. 850 mb temps will be in
the lower teens C first thing Monday morning, before dropping to as
low as 5C by first thing Wednesday morning. These temperatures aloft
should translate into highs mainly in the 60s, and lows in the 40s
and 50s.

- Dry and increasingly warmer late week; rain chances Saturday

We will see a transition to drier weather, with increasingly warmer
temperatures then for the Wednesday through Friday time frame, if
not through Saturday.

The upper low complex is going to get nudged east of the area on
Wednesday by an upper low digging across the western U.S., which
will sharpen an upper ridge and move it over the state. We can not
rule out a brief shower over the east on Wednesday, but most of the
area should be dry by then. We will then see a dry air mass move in
with plenty of subsidence under the ridge. This weather could
actually stall out over the area for a couple, to even possibly a
few days. That will depend on how the upper low over the East Coast
evolves. If it cuts off, we could see the ridge hold on over the
area longer, and rain chances hold off until after next Saturday. If
it does not cut off, the ridge would shift east of the area by
Saturday and allow rain chances to sneak in. There will be obviously
lots of fine tuning of the forecast over the next week.

&&

.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 618 PM EDT Sat May 25 2024

VFR conditions will continue at all the terminals tonight through
mid afternoon Sunday. SE winds will ramp up to 10-15 kts with
gusts to near 20 kts from late Sunday morning through Sunday
afternoon.

Scattered showers and thunderstorms will develop ate Sunday
afternoon into Sunday evening and could cause brief reductions to
MVFR/IFR. A stronger storm with briefly gusty winds is possible
mainly at our southern terminals late in the afternoon into the
early evening hours.

&&

.MARINE...
Issued at 328 PM EDT Sat May 25 2024

Light winds and fair weather conditions will continue through
Sunday morning before an offshore/southeasterly flow picks up
throughout the day. This probably won`t result in hazardous small
craft conditions, and certainly things will be fine along the
beaches, until low pressure passes to our north Sunday night and
reverses winds to a pronounced west-to-east direction. These
westerly winds will pick up especially after midnight Sunday
night and a small craft advisory will likely be needed for the day
Monday/Memorial Day for both winds and waves.

&&

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

&&

$$

UPDATE...04
DISCUSSION...NJJ/AMD
AVIATION...Laurens
MARINE...AMD