000
FXUS63 KGRR 140816
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
416 AM EDT Sun Apr 14 2024

.KEY MESSAGES...

- Mostly sunny and mild today/Monday

- Risk for Thunderstorms Remains Late Tuesday into Wednesday

- Turning Cooler Late Next Week

&&

.DISCUSSION...
Issued at 314 AM EDT Sun Apr 14 2024

Discussion reissued with corrected content below...

- Mostly sunny and mild today/Monday

Interesting little system moving across northern
Wisconsin/northern Lower early this morning. A strong surge of
warm air aloft coupled with robust mid level lapse rates is
helping to produce showers/storms over northern Wisconsin/northern
Lower. Present indications are such that almost all of the rain
will remain north of the cwa, but it`s possible that the northern
row of counties could get clipped with a few showers.

We`ll be solidly in the warm sector today and temperatures will
respond by climbing into the lower to mid 70s before the trailing cold
front moves through later this afternoon.

High pressure will build into the region Monday rendering clear
skies and slightly cooler temperatures compared today. However,
highs in the upper 60s will still be 10 degrees or so above
normal.

- Risk for Thunderstorms Remains Late Tuesday into Wednesday

An upper jet at 250 mb is currently digging into CA/NV and will move
east over the coming days, strengthening as it does so. By Late
Tuesday into Wednesday, Lower Michigan is likely to be positioned in
the left exit region of this upper jet, with upper divergence
present overhead. At 500 mb, models continue to forecast upper low
development over the Rockies and central Plains by late Monday into
Tuesday with a low level jet developing as well as surface
cyclogenesis. Surface low occlusion is forecast to quickly take
place shortly thereafter across the Midwest by Tuesday night. This
low is expected to track over Lower Michigan Wednesday. The
GEFS/CMC/ECE probabilities for measurable rainfall during this
period from Tuesday night into Wednesday is 90%-100% region-wide.

During the day Tuesday, not much may be happening as we await warm
air advection aloft and a rise in low level moisture. This may be
delayed until late in the day. Areas south of I-96 are most at risk
for some showers primarily after 18z Tuesday. Model trends seem to
be delaying this threat a touch so in a reality much of the region
may stay dry for a good portion of the day before a surface warm
front is slated to arrive Tuesday night. It is during the 00z-06z
Wednesday time frame that the environment may start to be conducive
to some showers and elevated thunderstorms.

Showers and some thunderstorms are likely to be ongoing at the start
of Wednesday morning. The ECMWF and GEM have slightly slowed the
arrival of a surface cold front across the region Wednesday
afternoon, which may give areas especially near and south of I-96 a
chance to build some surface based instability depending on what
happens with the morning activity. Numerous ensemble members as well
as the deterministic runs of the GFS and GEM show the potential for
1000+ J/kg of SBCAPE to develop. Tough to say at this point whether
this will be reality, but the risk is certainly there. Fairly strong
winds aloft at 850 mb (40 kts) and 500 mb (40-50 kts) could be
tapped with any convection that develops, though deep layer shear
does not look overly impressive at 30-35 kts. Still, thunderstorms
with strong wind gusts look to be the main hazard on Wednesday. With
a warm front lifting at least as far north as I-96, we`ll also have
to watch for potential for any surface based storms that can tap
into extra low level shear and storm relative helicity along that
boundary.

- Turning Cooler Late Next Week

GEFS mean 500 mb heights indicate troughing will be dominant across
the Great Lakes late in the week and weekend. Cold air advection at
850 mb looks to be slow but steady from Thursday into the weekend.
Declining temperatures at the surface can be expected during this
time as highs retreat into the 50s Thursday and Friday, then
possibly 40s for Saturday. Periodic rain showers are possible during
this time. Depending on cloud cover over the weekend, frost/freeze
conditions may develop.

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 122 AM EDT Sun Apr 14 2024

LLWS is well underway overnight as a 55 kt low level jet spreads
over the region, in the midst of weaker surface level flow. Wind
shear of 45-50 kts at 2000 ft can continue to be expected. This
threat will diminish in the 12z-14z time frame. Shower and
thunderstorm activity across NE Wisconsin and NW Lower Michigan
should stay north of all terminals overnight, but will maintain a
weather watch over Lake Michigan to see if any rogue showers or
storms develop south of that cluster of storms. Current odds are
low.

&&

.MARINE...
Issued at 413 AM EDT Sun Apr 14 2024

Strong winds aloft are getting mixed down to the surface near the
lake shore as evidenced by latest obs at MKG...g32 kts and
BIV...g39 kts. As such we have issued a Small Craft Advisory
through noon for the the lake shore south of Whitehall.


&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...Small Craft Advisory until noon EDT today for LMZ844>847.

&&

$$

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