674
FXUS63 KGRR 201949
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
349 PM EDT Thu Jun 20 2024

.KEY MESSAGES...

- Risk for Severe Storms through this afternoon

- Heat continues

- One or more rounds of Strong/Severe Storms possible Saturday
  into Saturday night

&&

.DISCUSSION...
Issued at 311 PM EDT Thu Jun 20 2024

- Risk for Severe Storms through this afternoon

SPC`s meso page shows ML CAPE values around 1500 J/kg extending
from near Grand Rapids to Lansing and down into the Jackson
region. Low level convergence is enhanced in this region and as a
result scattered storms have developed. These storms have produced
outflow boundaries some of which have collided. Effective bulk
shear was up to 25 knots and some organization has occurred with
the cells. High res models suggest the cells will gradually build
east so the risk for a few severe storms remains possible into the
late afternoon hours.

- Heat continues into Saturday

The low level thermal ridge remains over the southern and central
zones into Saturday. At the same time there will be plenty of
moisture in this warm air mass with PWAT values hovering in the
1.75 to 2.00 inches. Progged heat index values are shown to
continue to top out in the 93 to 97 degree range during this
timeframe. As a result we will keep the head advisory going.

- One or more rounds of Strong/Severe Storms possible Saturday
  into Saturday night

Parameters are coming together to warrant a greater risk for
severe weather during this time frame. Overall the models are
generally showing a stronger mid level wave digging into the area
in a pattern of stronger mid to upper level flow. A morning low
level jet could set off an MCS, especially over northern parts of
the CWA. A second low level jet arrives in the evening. Ensemble
surface based CAPE values from the models are showing at least
1000 J/kg in the afternoon/evening. With the potential for
stronger wind fields, favorable dynamics and instability, we may
end up with organized storms with stronger/organized wind gusts
being a main hazard. With several rounds of heavier rain possible,
values could be excessive.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 126 PM EDT Thu Jun 20 2024

Showers and storms are expected this afternoon, especially between
19Z to 23Z. All terminals except MKG could see TSRA. Some storms
have already started to develop in and around KGRR, AZO and BTL.
Between 18Z and 00Z is the timing of most concern. Potential for
fog overnight between 06Z and 18Z, especially southern TAF sites.

&&

.MARINE...
Issued at 311 PM EDT Thu Jun 20 2024

Overall, outside of any storms the winds and waves remain low into
Friday. On Saturday its looking like the winds and waves will be
building with a high potential for hazardous swim and boating
conditions arriving by evening.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Heat Advisory until 8 PM EDT Saturday for MIZ056-057-064>067-
     071>074.
MARINE...None.

&&

$$

DISCUSSION...MJS
AVIATION...Ceru
MARINE...Meade/04