339
FXUS63 KGRR 171516
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1116 AM EDT Mon Jun 17 2024

.KEY MESSAGES...

- Heat Advisory For Most Of Our Area Today - Friday

- A Few Showers and Storms Today

- Heat and Humidity Continue Through Mid to Lake Week

- Small Chances for Precipitation Mid Week

- Cooler Weather Behind a Cold Front Next Sunday

&&

.UPDATE...
Issued at 1116 AM EDT Mon Jun 17 2024

No changes needed to the forecast for today. Last part of the
convection from last night has held on over Jackson County this
morning. The supporting short wave/mesoscale convective vortex
continues to move away from the area, and so too will the more
organized shower/storm chances.

We have called around to the counties in the Flood Advisories, and
conditions are improving, and no longer a threat. So, we will be
cancelling the headlines very soon.

We could see a pop up shower/storm this afternoon with any kind
of mesoscale boundary. There is not going to be any bigger scale
forcing around to touch off convection. Plus, with the heat
becoming established over the area, we are becoming capped per
forecast soundings. Shear is minimal, so not expecting anything
severe. Anything would be a pulse type of storm, with locally
heavy downpours most likely with PWATs over 1.5 inches and slow
moving showers/storms.

Finally, no changes to the heat advisory either. Temps look to
warm into the low to mid 90s this afternoon under plenty of
sunshine. Dew points in the upper 60s and lower 70s will produce
heat indices of around 100F.


&&

.DISCUSSION...
Issued at 347 AM EDT Mon Jun 17 2024

- Heat Advisory For Most Of Our Area Today - Friday

It will be hot and humid today and again on Tuesday with
persistent southerly flow waa and as h8 temps moderate to 20 C.
This in conjunction with the amplifying upper ridge over the
eastern CONUS as h5 heights reach around 590 dM over our area
will result in high temps reaching into the lower to perhaps
middle 90s today and tomorrow.

This combined with dew pt values in the upper 60s to
lower 70s will result in heat indices reaching around 100 this
afternoon and early evening and again tomorrow. We have decided to
issue a heat advisory for most of our area as a result. Thx for
extensive coord on headline decisions DTX/IWX/APX.

- A Few Showers and Storms Today

Rain and thunderstorms are still in progress early this morning
over our se fcst area tied to the mcv that is moving slowly east
across that area. Severe wx potential has subsided overnight but
there is still potential for localized flooding given slow
movement of this precipitation across the same areas.

We expect pcpn to taper off over our se fcst area toward daybreak
with mostly dry conditions from mid to late morning into the
afternoon. A few showers and convection will likely redevelop
this afternoon with instability from daytime heating and perhaps
in the vicinity of boundaries from this early morning activity.

- Heat and Humidity Continue Through Mid to Lake Week

Heat and humidity look to continue mid to late week and likely into
Saturday as well. The upper level ridge actually builds into the
Southern Great Lakes mid to late week with 590+ dm 500mb heights.
850mb temperatures are not overly warm, but are largely in the +18C
to around +20C range. These values should push surface high
temperatures to around 90 or into the lower 90s from Wednesday
through Saturday. Surface dew points in the upper 60s to around 70
should push heat index values towards 100 at times through the
Wednesday through Saturday time frame. Heat Advisory looks good
at least through Friday. A prolonged heat event for sure.

- Small Chances for Precipitation Mid Week

There are small chances that we may see some shower and thunderstorm
activity spill into the forecast area at times, with the best of
those chances being Wednesday night into Thursday. It is this time
frame that a boundary sags into the area from the north. Both the
operational GFS and ECMWF show some activity making inroads into the
region. Do not think this will be an all day all night type of event
though and feel the headlines are still warranted this far out.
Could see the stout ridge winning out though and the better bet is
we will likely stay dry.

- Cooler Weather Behind a Cold Front Next Sunday

The heat at humidity that really began yesterday (Sat the 16th) will
likely stretch all the way to Saturday the 22nd. It is not until
Sunday when a pattern change occurs with an upper low pushing into
the Great Lakes along with a surface cold front. Models are fairly
consistent that the cold front will move through on Sunday. Sunday
night lows dip back into the 50s in parts of the area.

&&

.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 751 AM EDT Mon Jun 17 2024

Mainly VFR conditions are in place across the area at 12Z. This
will largely remain the case both today and tonight. There is a
chance for showers and thunderstorms this afternoon and early
evening. At this point given low coverage we only have VCSH in the
TAFs. The may be updated as conditions change. Southwest winds of
10 to 20 knots are expected today.

&&

.MARINE...
Issued at 347 AM EDT Mon Jun 17 2024

Winds and waves will remain below sca criteria early this week.
Southerly winds to around 15 to 20 kts will build wave heights to
around 2 to 4 feet across our northern nearshore zones with lower
wave heights further south. Isolated thunderstorms could pose a
hazard to mariners.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Air Quality Alert until midnight EDT tonight for MIZ037-043-050-
     056-064-071.
     Heat Advisory until 8 PM EDT Friday for MIZ043>046-050>052-
     056>059-064>067-071>074.
MARINE...None.

&&

$$

UPDATE...NJJ
DISCUSSION...Duke/Laurens
AVIATION...Duke
MARINE...Laurens