167
FXUS63 KGRR 021615
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1215 PM EDT Thu May 2 2024

.KEY MESSAGES...

- Chance for thunderstorms later today into Friday

- Warm and Mostly Dry Weekend

- Showers and Storms Tuesday/Tuesday Night

&&

.UPDATE...
Issued at 1114 AM EDT Thu May 2 2024

Isolated thunderstorm moving into Berrien County has not really
shown any signs of weakening. Its occurring on a wing of weak elevated
instability moving into the southwest parts of the CWA. We will
update the forecast to reflect a risk for an isolated thunderstorm
this afternoon for southwest zones. Instability builds this
evening and into tonight as low level wind fields strengthen.
Overall the instability still remains weak and deep layer shear is
relatively low. However models are showing increasing convection
overnight so high POPs remain warranted. Isolated stronger wind
gusts could accompany the storms.

&&

.DISCUSSION...
Issued at 347 AM EDT Thu May 2 2024

- Chance for thunderstorms later today into Friday

The first half of the day today should continue where Wednesday left
off with mild temperatures and some cloud cover in place. We will
see some smaller rain chances start to develop after noon for areas
further North and West. The reason this is the case is that the low
level jet that will be driving this round of showers and storms will
be focused much more to our NW. In addition, the lower level
moisture is lacking here, with a good deal of mid clouds moving
through. This is likely to result in a few sprinkles/light showers
falling from a mid cloud deck.

The best chance for rain will come later this evening and last
through Friday morning before starting to push east of the forecast
area. This is when the last part of the low level jet is exiting the
area, and moisture pooling ahead of the sfc front will be sufficient
for rain to be likely.

Thunder chances start to move over the area this afternoon, once
again further NW, closer to the low level jet and the better
moisture and warmth aloft. Some of the convection allowing models
are trying to bring MU CAPEs up into the 1500 J/kg toward midnight
tonight, supporting a thunder mention. The amount of instability is
likely what the Marginal Risk from the SPC is focused on. It is a
pretty healthy amount of instability present.

The limiting factors that will keep the storms likely on the more
tame side is due to the upper wave staying well west of the area.
This track will also take the core of the low level jet further
west. The entire system will take its time to move through the
entire area with the front almost nearly parallel to the upper flow.

- Warm and Mostly Dry Weekend

A secondary weak sfc cold front is shown to slowly drift in from the
west over the weekend as the nrn Plains upper low/trough moves to
Hudson Bay. Only 20-30 pct pops are in the forecast ahead of this
feature however due to lack of stronger forcing, and the bulk of the
weekend should be dry with warm temperatures in the 70s.

A weak sfc high and drier air mass builds in behind that front for
Sunday night into Monday and the baroclinic zone temporarily settles
just south of MI. Also an upper ridge builds overhead during this
time as next upper low/trough moves into the nrn Plains, suggesting
a dry day. However the warm front returns north again on Monday
night which brings a renewed chance of showers and storms.

- Showers and Storms Tuesday/Tuesday Night

A potentially active period is Tuesday afternoon and evening as a
shortwave heads northeast from KS and sends a front in our
direction. Moisture return from the Gulf via 40 kt low level jet
should result in numerous showers and storms developing and will
carry 60-70 pct pops. Fcst confidence in convective potential
decreases by the middle of next week with large ensemble QPF/timing
spread noted, but temps look to remain above normal.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1216 PM EDT Thu May 2 2024

Low pressure moving toward the Great Lakes will push clouds over
the terminals tonight. We`ll see high clouds this afternoon and
perhaps a weak shower passing close to AZO around 18z. Otherwise,
more showers/storms are expected tonight.

Models show a fairly strong signal of MVFR/IFR moving across the
termimals from northwest to southeast beginning around 07z at MKG
and lasting roughly 5 hrs before returning to VFR. This also
coincides with the showers/storms arriving and departing.

&&

.MARINE...
Issued at 347 AM EDT Thu May 2 2024

We are cautiously optimistic that we will not need any marine
headlines for the next couple of days. There is an increasing
pressure gradient coming in later today and tonight. This looks to
be offshore in nature, and will be warmer air riding up over the
cooler waters of Lake Michigan. Winds could be up around 20 knots,
just below criteria.

High pressure building over the area for this coming weekend will
give boaters a chance to get out on the waters with good boating
conditions expected.

&&

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

&&

$$

UPDATE...MJS
DISCUSSION...Meade/NJJ
AVIATION...04
MARINE...NJJ