951
FXUS63 KGRR 101749
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
149 PM EDT Fri May 10 2024

.KEY MESSAGES...

- Fair Weather Today

- Showers Tonight and Saturday

- Mainly Dry Sunday, But Some Showers and Storms Late

- Showers and a Few Storms Linger Monday into Tuesday

- Additional Rain Chances Thursday into Friday

&&

.UPDATE...
Issued at 1236 PM EDT Fri May 10 2024

Will add a few showers to the forecast to the north and east of
Grand Rapids in an area of convergence. The HRRR shows this zone
moving fairly quickly off to the east as the westerly surface flow
picks up. So, not expecting anything widespread or that will last
long into the afternoon.

An area of fog can be seen in satellite imagery over Lake
Michigan. We have added this to the forecast, but we believe it
will mix out fairly quick this afternoon.

Otherwise, we expect a partly cloudy sky with mainly dry
conditions this afternoon. Near normal highs in the 60s.

&&

.DISCUSSION...
Issued at 300 AM EDT Fri May 10 2024

- Fair Weather Today

Morning fog near and north of M-20 will mix out shortly after
sunrise. Shortwave ridging today will maintain benign weather with
diurnal cumulus developing inland from Lake Michigan. There is a low
chance of an afternoon shower or sprinkle east of US-131 and more so
toward US-127, as depending on the height of the mid-level cap on
the cumulus, cloud tops may reach -10 C per the HRRR, RAP, and ARW.
One has to wonder if there will be a short window of time favoring
dust devils around mid day, given the deep mixing layer and winds
under 10 knots, just before cloud coverage increases and winds
pick up during the afternoon.

- Showers Tonight and Saturday

An Alberta Clipper type trough will dig into the Great Lakes tonight
and develop a surface low over Lower Michigan and Lake Huron on
Saturday. A short period of rain is expected with a cold front
tonight. The HREF models peg the arrival of rain at the Lake
Michigan shore to be around or shortly after midnight, reaching
eastern parts of Michigan around daybreak. Daytime Saturday will be
breezy with west-northwest gusts around 25 mph. Showers and possibly
a few thunderstorm cells may develop with surface heating
particularly inland away from Lake Michigan.

- Mainly Dry Sunday, But Some Showers and Storms Late

Overall, Mother`s Day is shaping up to be mostly dry and mild,
though a bit on the breezy side with 15-25 mph winds. A few showers
can`t be ruled out near and north of U.S. 10 during the day. An
upper low over Hudson Bay will push a weak surface cold front into
the region Sunday night that will bring with it some showers and
perhaps a few elevated thunderstorms. A few hundred J/kg of elevated
instability looks to advect into the region as this front
approaches. Best chance for rain looks to occur after sunset Sunday
night.

- Showers and a Few Storms Linger Monday into Tuesday

The surface front won`t make a lot of southward progress into Monday
as upper heights begin flattening out and upper forcing moves away
from the region. However, ensemble and deterministic guidance
indicates an upper trough or perhaps closed low will progress over
the MO/IL vicinity by Tuesday, which may help force low level flow
to turn northeasterly and begin dragging down drier air into the
region. The timing of this is not yet certain, but ensemble
probabilities are hinting at a drying trend north of I-96 by early
Tuesday. GEFS 50th percentile 24 hr QPF amounts are about 0.10"-
0.25" region wide from 12z Monday to 12z Tuesday. The 24 hr period
ending 12z Wednesday shows locations north of I-96 almost totally
dry. In fact, the ECE 50th percentile QPF for this same period is
dry for the entire region, and even the 75th percentile is almost
totally dry from 12z Tuesday to 12z Wednesday. So, the best risk for
rain comes Monday into Tuesday especially near and south of I-96.

- Additional Rain Chances Thursday into Friday

Ensemble guidance is indicating a period of mid level height rises
over the Great Lakes Wednesday into Thursday out ahead of troughing
that is suggested to occur over the Great Plains by Thursday. The
ECE and GEFS mean 500 mb heights and vorticity are almost identical
with this pattern for a day 7 forecast, which adds confidence to the
synoptic pattern evolution. What this means for us is that rain
chances will likely be returning for the late week period, but
timing and amounts this far out are sketchy. The GEFS membership
looks quite a bit wetter than the ECE or CMC. Still plenty of time
to watch the ensemble trends.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 143 PM EDT Fri May 10 2024

Occasional VFR ceilings with bases around 5K feet today are
expected to continue, especially at inland locations. A line of
showers (maybe a rumble of thunder) late this evening could be
preceded by brief gusty southwest winds close to 30 KT, but once
the rain arrives winds will switch to the northwest. Some lower
MVFR ceilings are expected to develop after midnight - especially
at the northern terminals like MKG, GRR, and LAN and continue
through the morning Saturday. Northwest winds will probably get a
bit gusty during the day Saturday, with gusts reaching toward the
20 or perhaps 25 knot mark at times.

&&

.MARINE...
Issued at 300 AM EDT Fri May 10 2024

A small craft advisory may be needed for portions of the nearshore
Saturday and Sunday. First, there may be briefly gusty winds to 30
knots late tonight with a line of showers and cold front. Then,
sustained winds of 15-18 knots from the northwest on Saturday may
build waves to 2 to 4 feet, perhaps 3 to 5 feet between South Haven
and Grand Haven for a time. A stable marine air layer may limit gust
potential above 22 knots. Last, strengthening southwest winds on
Sunday may be hazardous for small craft north of Holland.

&&

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

&&

$$

UPDATE...Duke
DISCUSSION...Hoving/CAS
AVIATION...AMD
MARINE...CAS