749
FXUS63 KGRR 162311
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
711 PM EDT Tue Jul 16 2024

.KEY MESSAGES...

- Isolated mainly afternoon showers/storms through Wednesday

- Below normal temps Thursday into Friday

- Tranquil summer weather through the weekend

&&

.DISCUSSION...
Issued at 205 PM EDT Tue Jul 16 2024

- Isolated mainly afternoon showers/storms through Wednesday

The combination of low level convergence and instability this
afternoon and evening could touch off an isolated
shower/thunderstorm mainly for inland locations. The SPC`s meso
page shows surface based instability up to 1000 J/kg as of noon
which is forecast to climb closer to 1500 J/kg. Effective bulk
shear values remain low so if we do have any storms this
afternoon/evening they should remain pulse in nature.

As for Wednesday, the mid level cold pool sinks south into Lower MI
with a vort max moving in for the afternoon. Afternoon
instability builds once again but remains limited with surface
based values of 500-1000 J/kg. Thus a few storms could develop in
the afternoon or evening, but overall the coverage is expected to
remain limited. This is supported by the ensemble qpf values
showing little or no qpf.

- Below normal temps Thursday into Friday

A large area of high pressure moves into the Great Lakes Region
during this timeframe. Northerly flow in advance of the
approaching high will draw down some cooler air from Canada.
Models are showing the 925 mb thermal trough over the CWA then so
Thursday is likely to feature the lowest temperatures. Ensemble
max temperatures generally keep the region in the 70`s both days.
Ensemble min temperatures show overnight lows into the low to mid
50`s away from Lake Michigan.

- Tranquil summer weather through the weekend

The global ensemble fcst systems remain in fair agreement of
mostly uneventful weather for the weekend. Broad scale upper level
troughing will linger over the Great Lakes but with weak flow,
keeping the worst of the summer heat out west and humidity
suppressed to our south. There may be a gradual warming trend day
by day, though temperatures won`t stray too far from normal. A
weak mid level low nudging into the Midwest may bring a 10 to 20
pct chance of showers on Sunday. Most ensemble members keep CAPE
and QPF low until about next Tue-Wed.

&&

.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 711 PM EDT Tue Jul 16 2024

All sites are VFR as a mix of high clouds and pockets of cumulus
in the 6-8kft range cross the state. Cumulus subside overnight
before SCT to BKN pockets of cumulus at similar heights to today
redevelop on Wednesday. An isolated shower is possible near
LAN/JXN Wednesday afternoon but confidence in terminal impacts is
to low for TAF inclusion. Expect NW winds around 10 knots through
the TAF window with MKG gusting to near 20 knots Wednesday
afternoon.

&&

.MARINE...
Issued at 205 PM EDT Tue Jul 16 2024

With a large Canadian high pressure system building into Lower MI
Wednesday into Thursday, the cool and dry air advection in advance
of it commonly leads to hazards conditions for swimmers and small
craft.  We will go ahead with issuing a headline for this event to
give advance notice of the risks, focused on Wednesday afternoon
and evening. It`s possible that an offshore flow could develop
south of Whitehall and if that happens the larger waves may miss
Muskegon and Holland, but most models support hazardous conditions
for those sites as well.

&&

.HYDROLOGY...
Issued at 205 PM EDT Tue Jul 16 2024

The Grand River at Jackson has peaked and will fall below flood
stage this afternoon. Additional rainfall over the next couple of
days will stay under a tenth of an inch, limiting any additional
runoff. Rises are expected on some rivers from the rainfall over
the past few days, but at this time, no additional river forecast
points are expected to go above flood stage. Lingering long-term
flooding from high water levels on some lakes in southern
Michigan will slowly be able to drain with mostly dry weather over
the next week.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Beach Hazards Statement from Wednesday afternoon through late
     Wednesday night for MIZ037-043-050-056-064-071.
MARINE...Small Craft Advisory from noon Wednesday to 6 AM EDT Thursday
     for LMZ844>849.

&&

$$

DISCUSSION...MJS/CAS
AVIATION...Thomas
MARINE...MJS
HYDROLOGY...MJS