177
FXUS63 KGRR 141954
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
354 PM EDT Sun Jul 14 2024

.KEY MESSAGES...

- Showers and Thunderstorms this evening and again Monday night

- Diminishing Rain Tuesday then Cooler and Dry to End the Week

&&

.DISCUSSION...
Issued at 354 PM EDT Sun Jul 14 2024

- Showers and Thunderstorms this evening and again Monday night

Chose to roughly follow the HREF forecast for POPS tonight since
it seems to be a decent compromise for the wide range of
solutions in the CAMs. The idea is that convection will initiate
in the next few hours across Iowa and southern Wisconsin as an MCV
moves through an area where the airmass fully recovered from last
night`s convection. The storms move east and expand into another
MCS in WNW flow with the southern half or third of the forecast
area with likely POPs and some risk of severe weather, mostly
downburst winds.

These storms should be clearing the eastern forecast area around
06Z followed by a break in the action before the next round
arrives Monday afternoon as heights being to fall and surface cold
front settle south, with an MCS expected to form somewhere
upstream across the Dakotas or Minnesota and dive SE into
Wisconsin, northern Illinois and eventually southwest Lower
Michigan. The general signal in the synoptic pattern has been
there for several days, but the details on the mesoscale have
been quite variable and uncertainty remains. It seems the main
threat will be strong downbursts in a progressive type derecho
regime with the highest chance for severe winds across the
southwest forecast area, late afternoon Monday into Monday night.

- Diminishing Rain Tuesday then Cooler and Dry to End the Week

The cold front continues to get shoved southwards early in the day
Tuesday, then shower chances diminish by the afternoon. Upper
troughing moves in overhead with a weak shortwave presenting low
rain chances Wednesday afternoon across north central lower
Michigan. Surface high pressure builds in from the west Wednesday
evening with dry weather to persist through the end of the week.

Noticeably cooler conditions expected starting Tuesday following the
passage of the cold front Monday. Highs near 80 Tuesday, then into
the 70s through the end of the week. Dewpoints will also fall
resulting in less humid conditions. Overall, expect pleasant and
quiet weather with comfortable temperatures and plenty of sunshine
to end the week.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 136 PM EDT Sun Jul 14 2024

Showers and storms steered southwards across far southwest lower
Michigan and northern Indiana. While some patchy MVFR cigs
associated with the remnant showers are moving through, most areas
are VFR. Some new shower and storms activity is possible across
eastern MI this afternoon, but confidence is low so left it out of
this TAF cycle. Main sites that would be at risk for renewed
afternoon storms would be JXN and LAN.

Into tonight another round of showers and storms will move through
the area, but there is low confidence in coverage. General window
of possible storms will be from about 04z to 12z.

&&

.MARINE...
Issued at 354 PM EDT Sun Jul 14 2024

Winds and waves will continue to stay below hazardous levels for
mariners and swimmers, except for the potential for some strong
thunderstorms this evening and again Monday night. THese storms
could create locally higher waves and wind gusts over 35 knots.

Some areas of marine fog are also possible through Monday.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Air Quality Alert until midnight EDT tonight for MIZ050-056-057-
     064-071.
MARINE...None.

&&

$$

DISCUSSION...Ostuno/Thielke
AVIATION...Thielke
MARINE...Ostuno