020
FXUS63 KGRR 041150
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
750 AM EDT Sat May 4 2024

.KEY MESSAGES...

- Fog and stratus through this morning

- Showers and storms expected tonight

- Dry Monday, Otherwise Unsettled Most of Next Week

- Cooling Off Toward the End of Next Week

&&

.DISCUSSION...
Issued at 349 AM EDT Sat May 4 2024

- Fog and stratus through this morning

Our first focus out of the gate this morning is the fog/stratus that
is steadily spreading westward from SE Lower. This can be seen well
over the past couple of hours on the nighttime microphysics channel
as the thicker cirrus has thinned out a bit, and as the low
clouds/fog are moving west of the cirrus shield.

Our initial thought this morning is that stratus will be more
favored vs. fog. This moisture is advecting/expanding to the west as
low level moisture with the system yesterday did not make it far
east of the area. Then, as the flow has become more ENE, it is
taking that moisture and bringing it back over the area, or
expanding it to the area as the cooling atmosphere condenses.

There is a bit of wind aloft this morning, which is why we favor
stratus vs. dense fog. That said, winds have decoupled well, and a
couple of sites to our N and E have dropped down to less than a mile
in fog. We will continue to monitor the trends this morning. Once
the sunrises, the low level moisture will lift and mix out, probably
toward noon/early afternoon. Then there should be a fair amount of
sunshine and warmer air once again.

- Showers and storms expected tonight

The break in the weather we see today will be brief, with showers
and storms to become likely toward and after midnight tonight. We
will see a short wave try to approach the area tonight from the WSW.
This short wave will be weakening as it approaches the area, but
will hold on to enough of its strength the drive a cold front into
the area.

The cold front will be able to work with some instability ahead of
it, on the order of a few hundred J/kg of MU CAPE into the night.
Elevated LI`s are forecast to be around -1 to -3C ahead of the
front. Models are in fairly good agreement bring a broken line of
showers and storms through. With the instability being elevated, and
it being night time, severe weather threat is fairly low. Most of,
or all of this shower and storm activity should be east of the area
toward daybreak on Sunday. Clouds should clear out through the day,
and temperatures will climb up to around 70 with just a tad cooler
air coming in.

- Dry Monday, Otherwise Unsettled Most of Next Week

Guidance is in good agreement showing high pressure both aloft and
at the sfc in place on Monday, providing mostly sunny and pleasant
conditions with highs 70-75.  There is also still good agreement
that a shortwave and sfc cyclone will impact the area Tuesday
afternoon and night, with pops of 60-90 percent during this time.

Initially we see a warm front lifting north Tuesday afternoon but
then the cold front sweeps in quickly from the west Tuesday night as
a deepening sfc low tracks through WI. Can`t rule out some strong to
severe storms, but the main risk could end up being south of MI
since the warm sector may not make it this far north or stick around
long enough due to occlusion of the sfc system.

A period of dry weather is probable behind the Tuesday night system
for at least the first half of Wednesday, but another shortwave and
sfc trough associated with approaching longwave trough brings a
renewed threat of showers and storms by Wednesday evening. A repeat
of that is possible Thursday too as additional waves rotate through
the base of the nearing upper trough.

- Cooling Off Toward the End of Next Week

Unsettled/showery pattern persists through the end of next week as
the old nrn Plains upper low continues slowly eastward and
eventually sets up shop near Lake Superior. Our warm stretch finally
comes to an end by Thursday or Friday as progressively colder air
filters south around the upper low. Below normal temps appear likely
as we head into next weekend.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 750 AM EDT Sat May 4 2024

Areas of IFR/LIFR cigs and vsbys lingering through mid morning
before gradually lifting to a scattered to broken VFR cumulus
deck around 4500 ft. An isolated shower or tstm cannot be ruled
out inland from Lk MI in the late afternoon but the potential (and
the coverage) still looks too low to include in the TAFs. The
primary risk of showers and a few storms comes in from the west
after midnight tonight, but held off for now including any thunder
in the TAFs overnight. Another round of IFR stratus is quite
possible late tonight, after 09Z or so.

&&

.MARINE...
Issued at 349 AM EDT Sat May 4 2024

There is a potential that we may need a Small Craft Advisory for
later tonight into Sunday. It is then that the front will be moving
through, and a decent gradient sets up behind it from the NNW as the
high builds in from the west. Not confident enough yet at this point
to hoist an advisory.

Other than tonight, it looks like winds will generally stay under
thresholds with a lighter gradient in place.

&&

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

&&

$$

DISCUSSION...Meade/NJJ
AVIATION...Meade
MARINE...NJJ