784
FXUS63 KGRR 140612
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
212 AM EDT Fri Jun 14 2024

.KEY MESSAGES...

- Low/Medium Confidence on Severe Storms this evening

- Near Record Heat and Bouts of Heavy Rain possible next week

&&

.UPDATE...
Issued at 941 PM EDT Thu Jun 13 2024

The cold front wast dropping southward into northern parts of the
CWA near KRQB and KMOP. South of it the atmosphere remains
unstable so we could see an isolated storm or two develop. High
res models support most locations remaining dry though so we will
trend the forecast towards slightly lower POPs. Current satellite
trends support less cloud cover as well. Patchy fog may develop
as well as the recent rain has level southern parts of the CWA
with elevated surface dewpoints at this time. With less cloud
cover around we will see additional radiational cooling which
could also enhance the fog risk.

&&

.DISCUSSION...
Issued at 257 PM EDT Thu Jun 13 2024

- Low/Medium Confidence on Severe Storms this evening

Current radar trends show a line of strong to severe storms across
the Michigan U.P. along the cold front, while convection is just
starting to initiate across northern Illinois into western Lower
Michigan in an area of low level convergence combined with mid-
upper level ascent in the pre-frontal trough.

We expect that storms will initiate and begin to fill in across
central and southern Lower Michigan in the area of agitated cu
from Ottawa County to Gratiot County and then slowly drift
southeast ahead of the cold front, clearing the southeast forecast
area by 9 pm.

Downdraft potential energy and deep layer shear is sufficient for
a threat of at least isolated damaging winds, which could become
more widespread along an organized line of storms this evening as
the convection moves into a more unstable airmass that has not
been modified by Lake Michigan. That "lake shadow" effect could
inhibit stronger convection across the central forecast area,
decreasing the extent of severe storms there.

The cold front comes through later tonight with fair and cooler
weather for Friday and Friday night.

- Near Record Heat and Bouts of Heavy Rain possible next week

An upper level ridge will be building over the Great Lake region
through the weekend and through mid next week. The biggest concern
through this timeframe will be the building heat. Temperatures
may approach record high temperatures. The hottest day should be
Monday the 17th. Lansing, Kalamazoo and Battle Creek are currently
forecasted to be at or close to records. Grand Rapids current max
temp for Monday the 17th is within two degrees. Current record
for Grand Rapids is 95 (1994). The last time Grand Rapids airport
reached 95 or greater was June 21st, 2022.

This is expected to be the first period of 90 degrees or more for
this year. One of the concerns is the duration of the heat. There
are potentially three to five days in the 90s from Sunday through
Thursday. Lows through this period stay around 70 degrees so
maximum low temperature records are at risk as well from being
broken.

There is the potential through this period, Sunday through
Tuesday, that several Mesoscale Convective Systems (MCS) move
through the Great Lakes. The latest EC/GFS along with ensemble
means are trending toward a dome of High pressure setting up over
the southeast which will force moisture to stream over this high
through the region which could bring a steady stream of moisture
along with the warm air. So while periods of showers will be
possible the heat and humidity could create heat indices near 100.
This could allow for an extended period of Heat Advisory
Criteria.

As far as precipitation goes there is enough spatiotemporal
variability to not have large pops in any one period. However,
latest ensembles show a multi day period of +1 to +2 anomalous
PWATS over Michigan with PWATS upwards of 1.5 inches through this
timeframe. So there could be periods of showers/storms possible
late Sunday and late Monday. Given the hot/humid air mass, and
given the previously mentioned PWATS, heavy rain is a
consideration.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 212 AM EDT Fri Jun 14 2024

The main concern with this set of aviation forecasts is the
potential for some light fog along the I-94 TAF sites this
morning. A cold front stretches from near FNT to GRR to MKG at
06z. South of this front abundant low level moisture is in place.
Light winds combined with the low level moisture will result in
light for. At this point only included at JXN, but can see AZO and
BTL needed to be updated if the fog becomes pervasive.

VFR ceilings are expected throughout the forecast. High clouds
(bases at or above 15,000 feet) are expected the remainder of the
night with some broken cumulus today (bases around 4,000 feet).
Winds will become northerly (350-030) at all TAF sites tonight.
Wind speeds will be on the light side at 5 to 10 knots for the
most part.

&&

.MARINE...
Issued at 257 PM EDT Thu Jun 13 2024

Strong thunderstorms this afternoon and evening could bring
locally strong winds to 50 knots, hail and higher waves.
Otherwise, southwest winds to 20 knots this afternoon will
decrease overnight. Then winds will go north behind a cold front
on Friday to 20 knots and some choppy waves around Big and Little
Sable Points.

&&

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

&&

$$

UPDATE...MJS
DISCUSSION...Ostuno/Ceru
AVIATION...Duke
MARINE...Ostuno