401
FXUS63 KGRR 030603
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
203 AM EDT Fri May 3 2024

.KEY MESSAGES...

- Showers and thunderstorms into Friday

- Mild with several chances for showers/storms

&&

.UPDATE...
Issued at 1051 PM EDT Thu May 2 2024

Core of the instability has remained south of the forecast area
this evening. With the loss of daytime heating, the instability
has weakened and we do not expect a resurgence into the area
tonight. The RAP model only shows 100-400 j/kg of MUCAPE
overnight. So, we expect rain showers tonight with the potential
of isolated thunderstorms. The HREF continues to show pockets of
heavier rain developing ahead of the cold front that will move in
late from Wisconsin. Given the HREF has been consistent in showing
some half inch to one inch amounts there is a fairly high
confidence in this occurring from MKG northeast through RQB and
CAD especially. It will take much of the day on Friday for the
front to clear southeast portions of the forecast area near JXN.

&&

.DISCUSSION...
Issued at 304 PM EDT Thu May 2 2024

- Showers and thunderstorms into Friday

An upper level wave in the Upper Plains will track into the
Western Great Lakes tonight. It takes on a negative tilt as it
does. At the same time a low level jet will be tracking
northeastward through Western Lower MI, generating lower level
lift. Elevated instability will be present and PWAT values climb
to well above normal levels at around 1.5 inches. Given the
moisture, deep lift and presence of instability, showers and
thunderstorms will become numerous tonight. High res models
suggest several pockets of higher wind gusts could evolve
overnight, but most indications are that they may struggle to
reach severe criteria. The latest HRRR indicates the storms
developing around Chicago will build northeast and into our CWA
later this afternoon and into the evening. We did increase POPs
accordingly.

On Friday the front will be pushing eastward through the CWA by
mid afternoon. Thus any shower/storm activity will decrease from
west to east through the early to mid afternoon hours. At this
time the instability is progged to be limited so severe weather is
not anticipated.

- Mild with several chances for showers/storms

A persistent long wave trough over the Rockies will send a steady
stream of short waves toward the Great Lakes through the period.
Southwest winds aloft will also ensure that warm air flows across
the cwa. Highs will be in the 70s throughout the period and nudge up
to the 80 degree mark over the southwestern cwa Tuesday and Wednesday.

Saturday will probably be dry. However, a short wave moving across
the region may give us some showers and perhaps a storm Saturday
night.

Sunday looks dry, then another stronger wave arrives Monday night.
Strong low pressure over the northern plains is progd to push a warm
front north into the cwa late Monday night. We`ll likely see showers
and storms develop along/ahead of the warm front with more
development ahead of the trailing occluded front Tuesday.

Showers are possible again Thursday as the Plains low finally moves
over the state.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 203 AM EDT Fri May 3 2024

Showers and thunderstorms continuing overnight with the heavier
cells producing occasional MVFR or IFR vsbys and briefly gusty
winds. Otherwise generally high-base ceilings of 5000-8000 ft and
vsbys aoa 6 miles.

Toward daybreak as the sfc cold front nears looks for lower MVFR
to IFR cigs to arrive at MKG and GRR. This band of lower cigs with
the front will continue spreading east through the morning and
should impact each terminal for around 6 hours as scattered
showers continue.

Conditions improving to VFR Friday afternoon after the cold
frontal passage with winds shifting to the northwest around 10
kts. Will have to watch for the possibility of MVFR/IFR stratus
forming later Friday night, especially south and east of GRR.

&&

.MARINE...
Issued at 304 PM EDT Thu May 2 2024

With a low level jet track through the zones tonight the winds
will be on the increase. They are currently progged to remain
below criteria for small craft advisory so no headlines will be
issued at this time. Outside of the winds increasing over the
lake, gusty winds will accompany the showers and thunderstorms
that track through Lower MI tonight.

&&

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

&&

$$

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