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000
FXUS63 KGRR 130716
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
316 AM EDT Sat Apr 13 2024

.KEY MESSAGES...

- Sunny today/Sunday, chance of rain/storms tonight north.

- Warm Temperatures Early Next Week, But Turning Stormy

- Cooler Weather With a Chance for Showers Late Next Week

&&

.DISCUSSION...
Issued at 316 AM EDT Sat Apr 13 2024

- Sunny today/Sunday, chance of rain/storms tonight north.

High pressure is settling in over the state. Latest IR loop shows
clear skies across all but the far northern portion of the Lower
Peninsula. We`ll see abundant sunshine today and near normal highs
in the mid 50s.

The ridge will flatten out a bit tonight as a short wave moves
across northern Lower. A 45 kt LLJ will supply some moisture ahead
of the system. Elevated LI`s fall to around -4c while MUCAPE
climbs to nearly 1k j/k overnight across the northern half of the
cwa. Not a lot of surface-based instability, though. The northern
half of the cwa will be favored for precipitation. This is a quick
hitting system and will be out of the cwa by Sunday morning.

High pressure will quickly build into the region again leading to
sunny skies Sunday. H8 temps rising to around 12c should see
surface temperatures climbing into the 70s.


- Warm Temperatures Early Next Week, But Turning Stormy

Upper ridging early next week will briefly take hold of the region,
allowing for mild temperatures to stick around for a few days. NBM
guidance currently favors highs in the mid 60s to around 70 Monday
through Wednesday. By Tuesday, ensemble guidance and deterministic
models continue to indicate an upper low developing across the
central Plains and moving into the Midwest. At 500 mb, a split flow
pattern is initially favored across the Midwest but eventual phasing
of the upper low with another upper low diving southeast out of
Alberta is likely to occur Wednesday. Earlier guidance showed this
phasing and deepening occurring quicker and further NW of our
region, and current guidance indicates this phasing may occur
slower, and as a result the associated surface low is a bit slower
to arrive and further south as well. The translation here is that
precipitation may not begin until later Tuesday and could last
through late in the day Wednesday.

Increasing cloud cover is highly likely for Tuesday as a low level
jet takes aim at Lower Michigan and a surface warm front moves into
the region. Depending on the timing of precipitation arrival, we may
need to bump high temps down on Tuesday, but there is time to watch.
Surface flow looks primarily easterly now for Tuesday. Some weak to
modest elevated instability could work into the region, and combined
with some substantial low level shear could allow for some storm
organization that may pose a hail threat.

Additional thunderstorms are probable Tuesday night into Wednesday,
some of which could be strong to severe with strong winds and hail
depending on the degree of destabilization in the warm sector of
this system and how quick the surface low occlusion and cold air
advection on the back side of the system works into the region.
Timing of fropa is too uncertain to pin down, but that will prove
important for severe weather chances. Low and mid level jets of
around 50 kts are likely to impact the region, though orientation of
low level convergent flow may favor locations south and east of our
region. A limiting factor for this event may be questionable surface
based instability and also decreasing deep layer shear during the
day Wednesday, but both of these parameters are too difficult to pin
down at this juncture. The bottom line is that a risk for
thunderstorms remains Tuesday into Wednesday, and will need to be
watched closely in the coming days.

- Cooler Weather With a Chance for Showers Late Next Week

Upper troughing settles into the Great Lakes following this midweek
system, with distinct cold air advection occurring at 850 mb with
temperatures falling into the -5C to -10C range per ensemble
guidance. As this moves over Lake Michigan, enhanced cloud cover and
some lake effect rain and snow showers look possible by the end of
the week and weekend. There will be no impact from any snow showers
that may occur. By late next weekend, if any clearing were to take
place at night, a frost or freeze threat could materialize across
the region.


&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 112 AM EDT Sat Apr 13 2024

LLWS is enough of a threat overnight to include mention at LAN and
JXN where winds aloft are strongest and where surface winds have
continued declining. This threat should end by 09z or so.
Otherwise, the morning and afternoon hours will be marked with
somewhat breezy conditions but not nearly as strong as Friday was.
LLWS will again be a concern late in this TAF period as a strong
low level jet moves overhead and surface winds shift out of the
south. This is mainly expected to impact flights in the 03z-06z
range, but will likely continue a few hours beyond this TAF
period.

&&

.MARINE...
Issued at 316 AM EDT Sat Apr 13 2024

Winds continue to diminish and the end time of the Small Craft
Advisory still looks good. High pressure will settle over the
region today resulting in lighter winds and generally clear skies.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...Small Craft Advisory until noon EDT today for LMZ844>849.

&&

$$

DISCUSSION...04/Hoving
AVIATION...Hoving
MARINE...04