552
FXUS63 KGRR 151129
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
729 AM EDT Thu Aug 15 2024

.KEY MESSAGES...

- Showers/storms through Friday

- Rain chances persist into the Weekend

&&

.DISCUSSION...
Issued at 337 AM EDT Thu Aug 15 2024

- Showers/storms through Friday

Clouds will increase this morning as low pressure over the
northern Plains pushes an occluded frontal boundary toward the
region. Initially, the lower atmosphere will be fairly dry.
However, a seasonably strong LLJ will move over the cwa this
afternoon and we`ll see showers and isolated thunderstorms
develop. Generally, shear values remain aob 25 kts across much of
the cwa. However, models point toward the southwest cwa this
afternoon where shear values rise above 30kts. Any stronger
storms would likely be found southwest of a Grand Rapids to Battle
Creek line after 18z today.

The occluded front is progd to move across the cwa tonight in
conjunction with the leading edge of the upper trough and that
will likely produce more storms. Shear values climb to around 40
kts just ahead of the front, so we could see a strong to severe
storm late tonight.

The surface low and upper trough move over the cwa Friday, keeping
showers and storms in the forecast. While dynamics aren`t overly
strong, shear values are marginal enough for perhaps some cell
organization in a couple of the stronger storms; much of the cwa
is in a marginal risk for severe storms.

HREF ensemble probability matched mean qpf points toward the
northern cwa as the area that could see over an inch of rain
through Friday with the southern half in range for a quarter to
half inch.


- Rain chances persist into the Weekend

Upper troughing evolves into a cut off low over the Great Lakes
region by the end of the week. This will continue the chance of
showers through Sunday as sfc low pressure slowly moves through.The
rain should be ending by Sunday night as the low moves east.

Fair weather with below normal temperatures is expected next week as
northwest flow regime brings in an air mass of Canadian origin while
the heat and humidity remains bottled up across the SW CONUS. There
is a slight chance of showers by the end of next week as another
upper trough approaches from the northwest, but moisture is limited.

&&

.AVIATION /12Z TAFS THROUGH 12Z FRIDAY/...
Issued at 728 AM EDT Thu Aug 15 2024

VFR conditions will continue this morning then showers will move
in this afternoon from west to east with MVFR conditions by this
evening along with rain and a few thunderstorms. Southeast winds
will increase to 10 to 20 mph this afternoon.

&&

.MARINE...
Issued at 337 AM EDT Thu Aug 15 2024

As low pressure moves closer today, we`ll see winds increase from
the SSE this afternoon. We issued a Small Craft Advisory for this
afternoon through 06z Friday north of Grand Haven because that`s
where the wind and waves will be the highest. Wind and waves will
decrease late tonight.

Wind and waves will increase south of Holland Friday night and
Saturday behind the weak frontal boundary and a Small Craft
Advisory may be needed there during that time.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Beach Hazards Statement from noon EDT today through late tonight
     for MIZ037-043-050.
MARINE...Small Craft Advisory from noon today to 2 AM EDT Friday for
     LMZ847>849.

&&

$$

DISCUSSION...Ostuno/04
AVIATION...Ostuno
MARINE...04