999
FXUS63 KGRR 181125
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
725 AM EDT Tue Jun 18 2024

.KEY MESSAGES...

- Heat Advisory in Effect for Most of our Area

- Chance of Thunderstorms Today

- Heat/Humidity Persists Through The Work Week

- Small Chances for Precipitation Wednesday Night and Thursday

- Cooler Weather Behind a Cold Front Sunday

&&

.DISCUSSION...
Issued at 342 AM EDT Tue Jun 18 2024

- Heat Advisory in Effect for Most of our Area

Hot and humid conditions are expected again today and tomorrow
with continued south to sw flow waa and ridging in place. H8 temps
of around 19-20 C with ample sun the next couple of days will
result in high temps reaching the lower to middle 90s. This
combined with dew pts well into the 60s to lower 70s will yield
heat indices near 100 degrees. Therefore the heat advisory
headline remains in effect for most of our area.

- Chance of Thunderstorms Today

A consensus of latest CAMs and 00Z HREF all suggest that
convection over our far northern fcst area early this morning will
continue to drift ne and out of our area during the next hour.
Tranquil wx is then expected for most of the morning.

There is potential for an upper level disturbance and potential
mcv over far southern IL/IN to move to the nne and potentially
trigger convective development into our area by late morning. This
will be something to monitor as we will have at least 1000-1500
j/kg of sb/mu capes in place with relatively strongest instability
over our eastern fcst area.

Severe wx potential today looks low overall. However I would not
rule out isolated strong to severe convection with moderate to
strong instability this afternoon and model fcst soundings
showing strong low level lapse rates. However deep layer shear
remains low so this is mainly a pulse storm environment with
potential for localized downbursts.

- Heat/Humidity Persists Through The Work Week

We see no need to change our headlines regarding the heat on the end
time, which is currently 800pm Friday. 500mb heights remain high in
the 590s dm through the end of the week. The 592dm 500mb height
contour is all the way north of our entire forecast area at 18z on
Friday and you do not see that very often. 850mb temperatures via
the ECMWF, which is clearly the model to follow regarding
temperatures as the GFS has been low as we have ramped into this
heatwave, show values of +18C to +20C all the way into Friday. These
values should continue to produce highs around 90 into the lower 90s
potentially. We very much may need to extend the Heat Advisory into
Saturday as that looks to be the warmest day potentially of the
entire warm spell. 850mb temperatures spike to +22C. So, we are
staying the course on the current heat headline. We urge folks to
continue to check on people without air conditioning as there is no
relief at night (we sit at 81 degrees at 320am this morning in Grand
Rapids). Dew points are forecast to remain in the upper 60s to
around 70 so heat index values will make a run at 100 each
afternoon. The cumulative affect of the heat will add up as we
continue to move forward.

- Small Chances for Precipitation Wednesday Night and Thursday

A weak front will move into the area from the north Wednesday night
and Thursday with some small chances for showers and thunderstorms.
We do not think this will be enough to knock the heat down
significantly and therefore no changes to headlines. The ECWMF hints
at it and it may be the case where we do not see much in the way of
precipitation from this front. The ridge will be fairly stout at
that time with warm temperatures in the mid levels. Could see
precipitation being less and less in the models as we approach
Wednesday night and Thursday.

- Cooler Weather Behind a Cold Front Sunday

Models may be a tad quicker with the front that changes the airmass,
not moving in potentially late Saturday night. Either way, we will
see much lower dew points and cooler temperatures as we head into
the latter half of the weekend. The front will come with a chance of
showers and thunderstorms as it moves through. 850mb temperatures
drop back into the lower teens C on Sunday/Monday which will be
welcome after all the heat.

&&

.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 725 AM EDT Tue Jun 18 2024

A weather disturbance will move through Southwest Lower Michigan
today and bring mainly VFR clouds and scattered showers and
thunderstorms. The timing on the showers and storms will during
the afternoon after 17z to 18z. There may be some sprinkles that
move in from an area of light rain before that, but currently this
activity is not affecting visibility. All obs showing rain to our
south at this time have 10SM visibilities. Ceilings will lower
from unrestricted to 10,000 feet this morning and potentially to
4000-5000 feet this afternoon as showers and storms form. Tonight
we expect conditions to dry out and remain VFR. Winds will be
gusty from the southwest today at 10-20 knots with gusts to around
25 knots.

&&

.MARINE...
Issued at 342 AM EDT Tue Jun 18 2024

A small craft advisory and beach hazards statement is in effect
for the northern half of the lakeshore from this morning through
much of Wednesday. The southerly gradient will become sufficiently
strong enough to cause wave heights to reach around 3 to 5 feet
from Whitehall to Manistee. Wave heights will subside a bit late
this week as winds weaken somewhat.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Beach Hazards Statement through Wednesday afternoon for MIZ037-
     043-050.
     Heat Advisory until 8 PM EDT Friday for MIZ043>046-050>052-
     056>059-064>067-071>074.
MARINE...Small Craft Advisory until 4 PM EDT Wednesday for LMZ847>849.

&&

$$

DISCUSSION...Laurens
AVIATION...Duke
MARINE...Laurens