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000
FXUS63 KGRR 121457
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1057 AM EDT Fri Apr 12 2024

.KEY MESSAGES...

- Wind Increases This Morning

- Chance for Showers and a Few Storms Saturday Night/Sunday AM

- Warmer Next Week With Strong Storms Possible Tuesday/Wednesday

&&

.UPDATE...
Issued at 1057 AM EDT Fri Apr 12 2024

No real changes are needed to the forecast this morning. We did
tweak rain chances a little based on radar trends, and at least drizzle
being reported at just about all sites in the area. We are looking
at high rain chances with low additional amounts through mid
afternoon when the rain and drizzle should move east of the area.
Some clearing should take place late today as the clouds exit to
the east.

The main impact to the area today continues to be the expected
wind this afternoon. The Wind Advisory continues to look solid for
the entire area today. All sites are gusting 25 to 30 mph already
as of 10:30 am this morning. We expect that the winds will peak
roughly between 3 and 7 pm today with the best mixing and gradient
in place at that time. It is very possible that the advisory may
be able to be cancelled earlier than the current 2 am Sat
expiration time.

&&

.DISCUSSION...
Issued at 320 AM EDT Fri Apr 12 2024

- Wind Increases This Morning

A large low pressure system currently centered north of Lake Erie in
southern Ontario (as of 07z) deepens this morning as a mid-level
trough phases with a southern stream shortwave. Northwest surface
winds will ramp up considerably this morning as a tight pressure
gradient sets up over lower Michigan. Model soundings indicate a
deepening boundary layer while 40 to 55 knot 850mb winds build
across lower Michigan. Sustained northwest winds up to 20 to 30 mph
are expected today with peak gusts to 40 to 50 mph. The highest
winds are expected to occur inland, especially across north
central Lower Michigan where there is closer proximity to the
surface low.

In the meantime, rain showers will diminish in coverage as
moisture is steadily stripped away and PWATs fall to 0.5 to 0.75
inches. Light rain will linger this morning and early afternoon.
Another few hundredths to 0.25 inch of rain is expected for
today.

The surface low continues to progress northeast this evening with
showers ending late in the afternoon and winds gradually weakening
this evening and tonight.

- Chance for Showers and a Few Storms Saturday Night/Sunday AM

The forecast remains status quo for Saturday night into Sunday
morning with a chance for showers and a few storms mainly near and
north of I-96. A strong push of warm air advection aloft is forecast
to occur, with some increase in low to mid level RH as a weak
surface front moves through. Elevated instability on the order of
500-1000 J/kg is forecast, thus some thunderstorms may occur. The
00z NAM 3km appears to have an excellent handle on the expected
evolution of this precipitation, with showers and a few clusters of
storms moving through the region north of I-96 and exiting by mid
morning on Sunday.

- Warmer Next Week With Strong Storms Possible Tuesday/Wednesday

Little question that warmer temperatures are on the way with 60s and
70s overspreading the region Sunday into the middle of next week.
Synoptically, ensemble guidance is pointing to an impactful storm
system developing across the central Plains by Tuesday. GEFS mean
500 mb heights indicate a closed and negatively tilted upper low
moving into the Midwest by Tuesday afternoon and evening. What this
will do in the lower levels is push a warm front into Lower Michigan
sometime Tuesday. A vigorous 850 mb LLJ on the eastern side of this
upper low will crank 50-60 kt winds into IL/IN, pointing toward
southern Lower Michigan by Tuesday night, riding up over the surface
warm front. We may be looking at a high shear, low CAPE environment
setting up over Lower Michigan depending on where the warm front
sets up and the timing of the upper low`s movement. Sample GFS
soundings across southern Lower Michigan Tuesday afternoon and
evening near the vicinity of an expected warm front indicate 40-50
kts of 0-3 km shear, which is significant. A few rounds of
thunderstorms are looking likely Tuesday into Wednesday, some of
which may be strong to severe based on how the models are handling
the potential synoptic setup, though how much of this activity may
be elevated in nature vs. surface based is not entirely clear yet.
Nevertheless, this period of time does bear watching.

Beyond this period, ensemble guidance favors upper troughing moving
into Lower Michigan by Thursday or Friday. An additional chance for
some showers and perhaps some thunderstorms may exist across the
region until that upper trough moves through. Temperatures should
cool off late next week as this pattern transition occurs.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 740 AM EDT Fri Apr 12 2024

IFR made a resurgence in some areas this morning as ceilings
lowered slightly below 1000 ft. The IFR threat will mainly be
confined to this morning before ceilings gradually lift as a
strong pressure gradient will create significant wind gusts
throughout the lower levels of the atmosphere. Peak wind gusts
should reach around 40 kts this afternoon. Light showers or
drizzle are possible this morning before ending.

&&

.MARINE...
Issued at 320 AM EDT Fri Apr 12 2024

As a low pressure system to our northeast deepens, northwest
winds will build this morning with gusts reaching gales by mid to
late morning. Gale force winds will persist through this afternoon
and will gradually weaken this evening as the surface low moves
northeast. While winds will fall below gales tonight, winds and
waves will still be within Small Craft Advisory criteria through
Saturday morning.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Wind Advisory until 2 AM EDT Saturday for MIZ037>040-043>046-
     050>052-056>059-064>067-071>074.
MARINE...Gale Warning until 6 PM EDT this evening for LMZ844>849.

&&

$$

UPDATE...NJJ
DISCUSSION...Hoving/Thielke
AVIATION...Hoving
MARINE...Thielke