510
FXUS63 KGRR 171941
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
341 PM EDT Fri May 17 2024

.KEY MESSAGES...

- Summerlike Weekend

- Low Chance for Rain Sunday

- Active Early to Mid-Week Period

- Cooler End of the Week


&&

.DISCUSSION...
Issued at 340 PM EDT Fri May 17 2024

- Summerlike Weekend

Isolated/pulsing convection continuing through sunset in pattern
resembling mid-summer more than spring, featuring a weakly sheared
environment with respectable SB Capes of around 1500 J/KG.

Diurnally-peaking, random pop-up showers and storms will tend to
favor low level convergence zones and current radar/satellite
shows one such zone extending from AZO to MBS. Some of these could
contain small hail and briefly intense downpours though mid
evening per recent radar trends.

Once diurnal clouds/convection fade after sunset, patchy
fog/stratus is a good bet again tonight given elevated dew pts and
light winds. Locally dense fog is possible, especially near Lk MI
and in spots where any locally heavy downpours occur today.

Diurnal pop-up convection less likely on Saturday due to rising
heights and general subsidence pattern with sfc high in place.
Very summerlike start to the weekend after fog/stratus burns off
with highs in the lower 80s inland from Lk MI. There is a small
chance of showers/storms late Saturday night north and west of
GRR, related to a weakening band of convection moving southeast
from WI. Highs Sunday reaching the mid 80s which is more than 10
degrees above normal.

- Low Chance for Rain Sunday

Dry conditions carry into Sunday morning, then a weak front moving
across northern Michigan will sweep through the area acting as a
trigger point for showers Sunday afternoon. Limited moisture leads
to only a slight chance for precipitation, but widely scattered
showers or storms look possible.

- Active Early to Mid-Week Period

Better chances for precipitation are expected for the start of the
work week as a stronger upper level trough becomes established to
our west. Moisture advects into the region while several shortwaves
ride the larger upper level trough through the region. While showers
and storms are possible Monday, the better environment for storms is
expected Tuesday. A deepening surface low will move northeast from
the Southern Plains into Wisconsin with a trailing cold front
sweeping through the state. Ahead of that front, Michigan will sit
in the warm sector with a moist and very unstable atmosphere. Shear
will also be plentiful as a low level Jet noses into region Tuesday
evening. Uncertainty remains, but Tuesday will be a day to monitor
the thunderstorm activity and possible severe weather.

- Cooler End of the Week

Following the passage of the cold front Tuesday temperatures turn
colder to end the week. Uncertainty on how cool we`ll get increases
the latter half of the week, but the general idea centers around
upper troughing settling over the region with an 850mb thermal
trough driving down into Michigan. Current forecast expects peak
temperatures a touch below normal (normal highs are around 70
degrees) in the upper 60s to near 70.


&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 156 PM EDT Fri May 17 2024

Fog has diminished across the area this afternoon, with the last
of the fog lasting near and along the lakeshore. Expect fog to
redevelop late tonight to early Saturday morning with visibilities
down to 1/2 mile possible.

Isolated showers have begun to initiate along the lake front this
afternoon. These showers will move east through 00z this evening.
Sufficient instability with limited shear will mean short-lived
slow moving localized heavy downpours with a few rumbles of
thunder possible.

&&

.MARINE...
Issued at 340 PM EDT Fri May 17 2024

Fog has been plaguing much of the cool nearshore waters today and
while marine fog trends are very difficult to forecast, current
model guidance suggests it will stick around in one form or
another through at least Saturday morning. Have therefore
extended/expanded the Marine Dense Fog Advisory through Noon
Saturday. Otherwise winds/waves staying well below Small Craft
Advisory levels through the weekend.

&&

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

&&

$$

DISCUSSION...Meade/Thielke
AVIATION...Thielke
MARINE...Meade