363
FXUS63 KGRR 180733
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
333 AM EDT Sat May 18 2024

.KEY MESSAGES...

- Very mild weekend

- Low chance of showers late tonight and Sunday afternoon

- Wet Monday through Wednesday, Strong storms possible Tuesday

&&

.DISCUSSION...
Issued at 333 AM EDT Sat May 18 2024

- Very mild weekend

Summerlike conditions are forecast this weekend with high temps
reaching the low to mid 80s today and Sunday (except cooler near
Lake MI as a weak gradient is conducive for lake breeze formation
today and tomorrow). Ample sun is expected today after patchy
early morning fog with nothing more than some sct-bkn fair wx cu
late this morning and aftn mainly near to east of US-131.

- Low chance of showers late tonight and Sunday afternoon

A weakening line of showers and perhaps an isolated storm will
move in from the wnw into our nw fcst area very late tonight. The
vast majority of our area will not receive measurable rainfall
overnight.

Then for Sunday a weak frontal boundary will focus development of
a few showers and isolated storms mainly east to se of KGRR in
the aftn. Moderate instability will develop SE of KGRR with sb
capes reaching 1k-2k j/kg. However no svr wx is expected given
weak shear and weak forcing and limited moisture.

- Wet Monday through Wednesday, Strong storms possible Tuesday

Southwest flow aloft is usually a setup that can be stormy across
the Great Lakes during the spring and that will be the case here
Monday through Wednesday. Of the three days, Tuesday will garner the
most concern.

A short wave will track from the central Plains toward Wisconsin by
Monday morning along with a weak surface reflection. We`ll probably
see some showers and a few storms move over the lake and affect the
northwest cwa by Monday and afternoon with some of the convection
eventually drifting east Monday night. There`s decent
instability...MUCAPE around 1500 j/kg Monday afternoon and shear
values climb to around 35kts over the northwest cwa. So this area
may be favored late Monday for a few stronger storms.

A stronger short wave and surface low will emerge from the Plains
Tuesday and push a warm front through mid day Tuesday followed by a
cold front Tuesday evening. Bulk shear increases during the day
Tuesday and given the warm front moving through, spinups are a
concern. Dynamics are a bit stronger Tuesday night. However,
instability may be a bit weaker given the lack of heating. That
said, the models do show a mid level speed max around 65kts moving
across the cwa 06z Wednesday in conjunction with a 60 kt LLJ. The
evolution of this system bears watching.

Precipitation may linger through Wednesday as the upper low slowly
moves east. Overall, the Monday-Wednesday timeframe may be rather
wet with QPF in the 1-2 inch range.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 134 AM EDT Sat May 18 2024

Skies are clear across the region, but some fog is beginning to
develop along the lake shore. Short range models are not as
bullish on IFR vsbys as they were yesterday morning. We included a
tempo group for MVFR vsbys and we can adjust as conditions
warrant. Current dewpoint depressions are a couple of degrees
higher than last night at this time.

Any fog should burn off by 14z leading to VFR conditions the rest
of the period.

&&

.MARINE...
Issued at 333 AM EDT Sat May 18 2024

Patchy sporadic marine fog has been noted overnight and conditions
are conducive for more of it to develop this morning. Therefore
the marine dense fog advisory remains in effect through midday.
Otherwise winds and waves will stay well below Small Craft Advisory
levels this weekend.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Air Quality Alert until midnight EDT tonight for MIZ050-056-057-
     064-071.
MARINE...Dense Fog Advisory until noon EDT today for LMZ844>849.

&&

$$

DISCUSSION...Laurens/04
AVIATION...04
MARINE...Laurens