078
FXUS63 KGRR 121725
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
125 PM EDT Fri Jul 12 2024

.KEY MESSAGES...

- Scattered showers/storms possible again this afternoon/evening

- Mid summer heat/humidity/storm chances Saturday through Monday

- Cooling off mid next week with an upper trough

&&

.DISCUSSION...
Issued at 353 AM EDT Fri Jul 12 2024

- Scattered showers/storms possible again this afternoon/evening

Somewhat of a repeat of yesterday afternoon and evening is
possible today. An upper trough will be in place to start today,
however it will slowly be pivoting to the east as we work through
the day. Enough instability will occur again today through a
combination of cool temperatures in the mid levels and July
sunshine providing steep low level lapse rates. MAx surface based
CAPE this afternoon is actually forecast to eclipse 2,000 j/kg via
the HREF. 4 hour max reflectivity tells the story with scattered
convection occurring area wide this afternoon and evening. The
convection will likely focus 1) on the lake breeze front and 2) in
the northeast CWA closer to the upper trough center where the HREF
has the highest neighborhood probabilities of higher DBZs. Deep
layer shear of only 20 knots and zero updraft helicity swaths
indicates the severe threat is almost non existent. The
precipitation should come to an end in the late evening as we lose
instability.

There is a signal late tonight once again especially towards I-94
in our Consensus of Short Term models for fog formation. It is not
showing stratus, but shallow fog.

- Mid summer heat/humidity/storm chances Saturday through Monday

As discussed yesterday a ridge rider pattern exists between
Saturday and Monday which is indicative of deep summer featuring
heat, humidity and occasional chances for strong thunderstorm
complexes. Not much change in tonight`s models so confidence is
high in this pattern setting up. Both the GFS and the ECMWF show
shortwaves rolling southeast in the northwest upper flow with the
look of being convectively driven. Several rounds of showers and
storms are possible during this 3 day period. The most likely time
frames will be 1) Saturday night into Sunday morning and 2) Sunday
night into Monday morning. We will be near the nose of the
nocturnal 850mb low level jet both periods which is a major driver
of our thunderstorm chances. A combination of strong instability
in excess of 3000 j/kg and deep layer shear occasionally hitting
40 knots make severe weather very plausible. We are in a SPC
marginal outlook for Sunday, but envision this increasing as we
get closer in time.

- Cooling off mid next week with an upper trough

We cool off in the mid week time frame. Heat Sunday into Monday
will likely have us in the 90s, while we cool back into the 70s
for Wednesday and Thursday. The GFS has a +24C 850mb temperature
Monday midday which is a fairly rare level for us. By Wednesday
night the GFS is down to +8C overhead. A pretty big shift in
temperatures is due to a pattern change aloft from ridging to a
developing deep trough overhead. Right now we have a dry forecast
for Wednesday and Thursday, but could see some diurnal activity
possibly due to cool mid levels.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 125 PM EDT Fri Jul 12 2024

VFR conditions will prevail this afternoon but scattered showers
and thunderstorms could bring brief MVFR conditions, mostly
between 21Z and 02Z. Then areas of MVFR and IFR expected between
06Z and 12Z in fog and low stratus. That should dissipate shortly
after 12Z with VFR conditions prevailing on Saturday.

&&

.MARINE...
Issued at 353 AM EDT Fri Jul 12 2024

Very benign conditions typical of mid summer are expected on Lake
Michigan today, tonight and Saturday. Winds less than 10 knots and
waves a foot or less are anticipated through Saturday. A return
flow sets up on the backside of a departing high Saturday night
with southwest winds Saturday night and Sunday become westerly
Sunday night. Sunday and Sunday night are probably the first
forecast periods where advisory levels are even on the radar. That
said, at this time the WaveWatch3 has wave heights in the 2-3 foot
range. Bottom line, the latter half of the weekend into early next
week will need to be monitored for stronger winds and larger
waves. The GFS has 20-30 knots of wind from the southwest from
Saturday night through Monday. We will see how much of that mixes
down in a warm air advection pattern as we get closer to that time
frame.

&&

.HYDROLOGY...
Issued at 353 AM EDT Fri Jul 12 2024

3 River Flood Warnings remain this morning and they
are...Vicksburg on the Portage River...East Lansing on the Red
Cedar and Holt on Sycamore Creek.

All 3 are tracking well. East Lansing should crest today, Holt has
already crested and should fall below flood stage today and
Vicksburg is steady near Flood Stage.

The one site we are keeping an eye on is Burlington which is
closing in on flood stage and is near crest now. We will be
monitoring this site today.

&&

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

&&

$$

DISCUSSION...Duke
AVIATION...Ostuno
MARINE...Duke
HYDROLOGY...Duke