606 
FXUS63 KGRR 301901
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
301 PM EDT Fri Jun 30 2023

LATEST UPDATE...
Short Term/Long Term/Marine

.SHORT TERM...(This evening through Saturday night)
Issued at 300 PM EDT Fri Jun 30 2023

With the dissipation of the low clouds and fog this morning and
left over moisture from yesterday, it is actually quite humid out
there with temps also rising well into the 80s. The other notable
difference is that the smoke from the last couple of days has 
improved a fair amount. 

Forecast soundings for 18z show a fair amount of instability
present with temps in the 80s and dew points in the lower 70s. MU
CAPEs are pushing 3,000 J/kg this afternoon. The trend this
afternoon is for the atmosphere to stabilze a fair amount as the 
low level moisture is forecast to mix/move out a bit. 

This is important as we have a MCV near the Quad Cities from 
earlier convection moving toward far Southern Lower for this 
evening. The short term models and CAMs indicate that a few
showers and maybe a storm will be possible south of I-96 after
about 22-00z this evening. The other limiting factor for any rain
will be a lack of rich moisture in the column. The sfc is moist,
but that should mix out. The MCV should move out after 04-06z.
Some fog will be possible with any lingering low level moisture,
and light winds expected overnight.

We can not rule out a shower or storm coming in from the NW late
tonight and Sat morning. Another weak short wave will be moving
through the nearly zonal flow over the area. Not much instability
to speak of at that time of the day, and only mid level moisture
is expected to be present. 

This weak wave coming in late tonight and Sat morning should be
starting to exit the area by early in the afternoon. This is not
optimal for diurnal convection. It does look like 1000-1500 J/kg
of CAPE will build Sat afternoon away from the lake. Any kind of
boundary could touch off a shower/storm, but coverage is expected
to remain isolated to scattered at best. Deep layer shear looks
quite weak also to keep any storms of the pulse variety.

Additional rain chances will then come in beginning late Saturday
night for the southern third of the forecast area. The models have
been pretty consistent in bringing a mid level short wave trough
into the area beginning by 12z Sunday. Ahead of this mid level
wave, a sfc low will track south of the state. We will see the
northern periphery of the rain storms with this system come up to
no further north than I-96. Thunder chances look fairly low given
the time of the day, and less than 1,000 J/kg of MU CAPE available
on the cool side of the system.


.LONG TERM...(Sunday through Friday)
Issued at 300 PM EDT Fri Jun 30 2023

Fairly good model agreement on the evolution of the large scale flow 
regime over the next week with shortwave upper trough over the 
weekend replaced by flat ridging early to mid week then broad 
longwave trough by the end of the week.

At the start of the period we will see a continuation of the 
baroclinic zone and resulting MCS "bowling alley" across the Ohio 
Valley with some expansion northward into Lower Michigan on Sunday 
as an upper low or shortwave trough axis moves through with weak sfc 
reflection tracking just south of the forecast area. 

Surface and upper ridging builds in early next week with only slight 
chance POPs by Tuesday the Fourth. Moisture pooling in front of an 
advancing cold front/seasonably strong shortwave trough will set the 
stage for what could be widespread rains and convection after the 
Fourth. Trends, especially in the GFS, are faster with this feature, 
which could bring showers and storms into West Michigan by Wednesday 
afternoon, lasting into Thursday. Drought-alleviating rains possible 
here with precipitable water values progged to be above 1.8 inches 
during that time. Cool and dry Canadian airmass to follow for the 
end of the week.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 126 PM EDT Fri Jun 30 2023

Generally expecting better conditions with less impact for this
forecast period, with less smoke anticipated. It does look like we
will have some fog to deal with for tonight. 

Low clouds, and a mixture of fog and smoke that affected the area
earlier has vastly improved over the last 2-3 hours. The low
clouds and fog has dissipated, with a little bit of smoke/haze
lingering and causing mostly MVFR to VFR conditions. We expect
these conditions to improve a bit more this afternoon with less
smoke in place. Still quite a bit of humidity in place, which will
limit visibilities from becoming P6SM. 

There will be a chance of some rain showers mainly along the I-94
corridor this evening as a wave of low pressure moves by just
south of the area. It does not look to be impactful at this time
with mainly VFR to high end MVFR conditions expected. Can not rule
out a rumble of thunder, but that should stay mainly South.
Otherwise, most locations have a decent chance of some fog
overnight with the moist conditions in place and light winds
expected. This should burn off by mid-late Saturday morning.


&&

.MARINE...
Issued at 300 PM EDT Fri Jun 30 2023

We will be holding on to the Marine Dense Fog Advisory as is for
now. A lot of the fog over the lake has dissipated. However, the
visible satellite imagery shows fog/stratus hugging the coast
still. Webcams show dense fog still in place south of Little Sable
Pt. We will watch for the potential to cancel it early, or extend
it if needed. There is a chance it will redevelop tonight with a
light wind regime and dew points in the 60s/70s over the cool Lake
Michigan water. 

Other than the fog, it looks like we should stay fairly quiet with
regards to wind and waves. We do not anticipate needing any Small
Craft Advisories or Beach Hazards through this extended holiday
weekend.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...Dense Fog Advisory until 8 PM EDT this evening for LMZ844>849.

&&

$$

SHORT TERM...NJJ
LONG TERM...Ostuno
AVIATION...NJJ
MARINE...NJJ