415
FXUS63 KGRR 192250
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
650 PM EDT Thu Sep 19 2024

.KEY MESSAGES...

- Chance for Storms Tomorrow

- Several Chances of Showers and Storms into Next Week

&&

.DISCUSSION...
Issued at 252 PM EDT Thu Sep 19 2024

- Chance for Storms Tomorrow

Clouds begin to increase late tonight as an upper low tracking from
the Northern Plains into Manitoba sends a trailing front towards
lower MI, arriving in our area Friday afternoon and evening.
Spotty showers will begin to move through the area around late
morning to mid- day, then storms will be possible during the
afternoon. Diurnal instability up to 1000 to 1400 J/kg (highest
over southern lower MI) and bulk shear to 35 to 40 knots will
support a few strong storms, with the highest chance in far
southwest lower Michigan. Damaging wind gusts will be the primary
concern with any strong storms.

- Several Chances of Showers and Storms into Next Week

The weekend starts off dry as a period of brief ridging and high
pressure advects dry air across the area. Precipitation chances then
increase later Sunday and especially Sunday Night into Monday. This
is driven by a closed low over the southwest US ejecting into the
main flow pattern and bringing ample moisture with it. Can`t even
rule out a bit. Ensemble CAPE forecasts suggest the chance of
isolated thunderstorms also exists. Grand Ensemble precipitation
probabilities show the chance for a needed soaking rain is definitely
there. Chances of over 0.5" of rain Sunday Night into Monday night
is 40-60 percent and over 1 inch is around 10 percent.

This weekend into into next week marks the start of a pattern shift
as the ridge that has brought dry weather for over a week breaks.
This change makes troughing the predominant upper-level setup.
Several additional chances of rain are possible over this time
period, however as is common with these setups, the timing of the
shortwaves and associated rain showers is still not nailed down.
Thermal troughing also causes 850mb temperatures falling to around
10C, translating to a near normal low to mid 70s for highs next week.

&&

.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 650 PM EDT Thu Sep 19 2024

VFR conditions will continue at all the terminals this evening and
overnight. Fog is not expected overnight given that some light
winds will persist near ground level with stronger winds aloft.

Clouds will gradually move in Friday and scattered showers and
isolated storms will develop at our western terminals around or
shortly after midday and then by around mid or late afternoon at
our eastern terminals. Brief reductions to MVFR and perhaps IFR
are possible in heavier showers and isolated storms.

&&

.MARINE...
Issued at 252 PM EDT Thu Sep 19 2024

A weak cold front will bring a chance for scattered showers early
Friday morning. Otherwise, expect offshore winds starting Friday
with winds shifting southerly then westerly Friday afternoon
following the passage of the front. Wave heights stay generally low
through this weekend, with the highest waves to around 2 feet Sunday
evening.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...None.

&&

$$

DISCUSSION...Thielke/Thomas
AVIATION...Laurens
MARINE...Thielke