-- Discussion containing changed information from previous version are highlighted. --
395
FXUS63 KGRR 040520
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
120 AM EDT Tue Jun 4 2024

.KEY MESSAGES...

- Small Chances of showers/storms through Tuesday evening

- Showers and thunderstorms Wednesday, unsettled the rest of the week

&&

.UPDATE...
Issued at 950 PM EDT Mon Jun 3 2024

Raised pops considerably around Ludington and Pentwater earlier
(to 60-90 percent) where widespread showers have been streaming
northeast from the strong/svr convection over srn WI. That
convection has been largely diurnally driven so as the activity
there diminishes we should accordingly see pops tail off here as
well overnight. Otherwise a dry forecast has been maintained from
GRR to the south and east where dry/stable air mass continues to
prevail.

&&

.DISCUSSION...
Issued at 317 PM EDT Mon Jun 3 2024

- Small Chances of showers/storms through Tuesday evening

An initial look at the regional radar imagery looks ominous this
afternoon with a couple of lines of showers and storms over
Wisconsin. This, while we enjoy a mostly sunny and mild late spring
day. The showers and storms over Wisconsin look like they will stay
west of the area through the daylight hours, then maybe clip the far
NW portion of the area this evening and tonight.

First of all, the area has almost zero instability, except just
enough to pop some shallow cumulus development. The mid and lower
levels are quite dry, and the mid levels are capped nicely still
with a subsidence inversion. Also, the features driving this
convection in WI are a weak mid level short wave and low level jet.
Each of these features are forecast to move to the NNE, and barely
clip Mason, Oceana, and Lake counties this evening. By then, some
instability tries to develop, but is lost with the loss of the
heating of the day.

The trend for Tuesday and Tuesday evening has been for less chances
of rain during this period. A little more instability is expected to
be present/develop with diurnal heating on Tuesday afternoon. The
best instability will be across the NW corner where the theta e axis
ahead of the incoming front is clipping the area. The problem for
convection on Tuesday is mostly that there is no real feature to
touch off convection. Short wave ridging is a bit more pronounced,
and will squash most any updrafts that try to build. The only other
possibility would be where there may be some enhanced convergence
along the lake breeze.

Shower and storm chances will increase overnight Tuesday night. This
will be the result of short wave energy with the main trough
approaching later in the night. The low level jet however will be
mostly north of the area, and instability is almost nil per MU CAPEs
of less than 400 J/kg. This looks to be mostly shower activity that
would move in after midnight.

- Showers and thunderstorms Wednesday, unsettled the rest of the week

A negatively tilted upper wave will break above the western Great
Lakes, providing ample upward vertical motion (UVM) that will be
coupled with forcing from a surface cold front moving through the
region early in the day Wednesday. Conditional instability will be
augmented by the UVM; if this wasn`t occurring when diurnal
stabilization is maximized, we could be looking at more robust
convection. In the present case, however, instability should be
limited and low level forcing modest prior to convection exiting our
forecast area to the east. Hence, SPC is understandably not too
bullish in their Day3 convective outlook for our area.

As noted before, we will be in a persistent upper trough/closed low
scenario the rest of the work week. This means unsettled conditions
with seasonably cool temperatures and also unclear details regarding
quantity and timing of precipitation episodes. Advertised rain
chances Thursday and Friday are in the 20 percent range to basically
serve as a hedge against the uncertainty.

However, there is somewhat better certainty regarding the upper low
exiting east of the western Great Lakes by this weekend, meaning
drier northwest flow aloft. But, this of course is predicated on the
upper low being well handled by the models beforehand.

&&

.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
-- Changed Discussion --
Issued at 1259 AM EDT Tue Jun 4 2024

Showers continue to weaken as the cross Lake MI west of KMKG.
However, over the next couple of hours, there will likely be some
in the vicinity of that airport. After that, patchy fog remains
possible over the interior parts of Lower MI. Conditions will
likely fall into the MVFR range, but very local IFR is a
possibility that we will be monitoring through the night.
Instability will be on the increase Tuesday, mainly over western
parts of Lower MI. We will have to monitor any lake breeze that
tries to develop. That feature could provide enough low level
convergence to generate an isolated storm. Overall though that
potential is too low at this time to add any thunder to the
aviation forecast.
-- End Changed Discussion --

&&

.MARINE...
Issued at 317 PM EDT Mon Jun 3 2024

We do not expect to need any advisories into Wednesday.

The fog that was problematic yesterday through this morning moved
offshore with the flow from the SE, and then dissipated. We do not
expect a repeat performance tonight with winds being a bit more
steady with the approach of the next system.

The increasing winds are expected to stay tame enough to not need
any Small Craft Advisories into early Wednesday. We expect that
winds will stay below 20 knots, and waves will stay below 4 ft. The
next expected advisory will likely come in the wake of the Wednesday
front with much cooler air coming in on a stronger gradient.

&&

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

&&

$$

UPDATE...Meade
DISCUSSION...NJJ/TJT
AVIATION...MJS/Ceru
MARINE...NJJ