901
FXUS63 KGRR 141144
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
744 AM EDT Tue May 14 2024

.KEY MESSAGES...

- Scattered showers/isolated thunder today, then dry

- Showers with a Few Storms Thursday Night into Friday

- Occasional Storminess Possible Sunday into Early Next Week

&&

.DISCUSSION...
Issued at 324 AM EDT Tue May 14 2024

- Scattered showers/isolated thunder today, then dry

Radar continues to show very light rain showers/drizzle over the
the northern cwa north of the frontal boundary that stretches
east/west along I-96. These showers are closer to the h8 front. On
the surface, temperatures north of the front are in the mid 50s
with dewpoints in the 40s, compared to lower 60s/mid 50s south of
the front.

GFS/Nam3km show a weak wave on the front this morning that moves
south during the early afternoon. This should help to drag the
frontal boundary through the cwa during the afternoon. Instability
is pretty meager today, highest along the southern row of the cwa
where MUCAPE around 200 j/kg were noted in the models. An isolated
thunderstorm isn`t out of the question today, but most of the
precipitation will be just showers.

Aloft, a trough is moving across the Ohio Valley and once it moves
to the east late afternoon/early evening, we`ll see rain chances
end. High pressure will nose into the region from Ontario tonight
and help to clear out the sky and set the stage for sunshine
Wednesday.

Highs will range from the mid 60s to around 70 today and in the
70s Wednesday.

- Showers with a Few Storms Thursday Night into Friday

A 500 mb shortwave trough will move into the Great Lakes late
Thursday into Friday, but will be weakening as it does. LLJ
orientation and strength is more impressive on the 00z GFS and GEM
compared to the ECMWF, and not surprisingly there is greater
coverage of showers from both of those models. Given the weakening
trough in the upper levels, there is very little surface reflection
or change in pressure/temps/dew point as this feature moves through,
other than a slight dip in MSLP and a veering of winds from easterly
to southerly. Some modest instability is present, mainly elevated,
so a few thunderstorms may occur. Total rainfall amounts look
varied, but generally 0.25"-0.50" is forecast. The 00z GFS is likely
overamplifying the base of the trough Friday into Saturday and
creating a surface wave riding along the front. This is not
supported by the ECMWF and GEM, nor the GEFS mean 500 mb heights. As
such, the prolonging of showers on the GFS well into Saturday is not
favored at this time. Drying conditions are more likely to occur
than rain on Saturday.

- Occasional Storminess Possible Sunday into Early Next Week

Less than desirable model consensus exists regarding the synoptic
pattern beginning Sunday, and poor agreement is in place not only
between different model systems but even model run consistency
within an individual system (ie. ECMWF). The GEFS mean 500 mb
heights and wind speeds show upper ridging working in Sunday into
Monday with increasing mid level jet speeds closer to next Tuesday,
and 24 hr QPF (50th percentile) favors mainly dry conditions Sunday
into Monday. The ECE 50th percentile QPF supports some rain over the
region Sunday into Monday. This far out, low POPs seem the best way
to go.

There are hints that low and mid level jet cores could be
strengthening over the central U.S. early next week, helping draw up
low level moisture flow into the Upper Midwest and potentially the
Great Lakes as well. The difficulty is anticipating which days have
a greater risk for showers/storms than others. The 00z ECMWF would
present probably the worst case scenario with multiple rounds of
showers and thunderstorms beginning late Sunday and lasting into
midweek. Given some of the run to run issues with the ECMWF as of
late, that may be overdone. Still, early next week will be an
interesting period to watch if stronger synoptic support for storms
materializes.

&&

.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 743 AM EDT Tue May 14 2024

A batch of lower ceilings has indeed materialized in and around
LAN as of this writing, and IFR has occurred. Whether this will be
a predominant condition into the morning is questionable, so have
opted to include as a TEMPO group and will continue monitoring.
These low ceilings at or below 700 feet are patchy across the mid
Michigan area. Have included SCT mention at GRR as well as JXN as
low level flow is easterly, and could bring a risk for IFR at
those sites as well if conditions worsen more than expected.
Scattered showers will be traversing the region into the afternoon
hours, and brief reductions to 2sm-3sm are possible in any
showers that develop.

&&

.MARINE...
Issued at 324 AM EDT Tue May 14 2024

Northeast winds behind the frontal boundary may lead to a brief
period of higher waves west of the Points today; have opted not
to include a headlines due to the limited nature of the threat.

A weak pressure gradient will preclude higher wind/waves in the
nearshore waters for the next few days.

&&

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

&&

$$

DISCUSSION...04/Hoving
AVIATION...Hoving
MARINE...04