694
FXUS63 KGRR 170545
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
145 AM EDT Wed Jul 17 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 /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 145 AM EDT Wed Jul 17 2024

Some patchy/shallow ground fog cannot be completely ruled out
early this morning where any lengthy/persistent breaks in the
cloud cover occur. Otherwise VFR weather is expected the next 24
hours with sct-bkn clouds between 6000 and 8000 ft. Northwest sfc
winds increasing to 10 to 20 kts and gusty this afternoon then
subsiding below 10 kts after sunset this evening.

&&

.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 this afternoon through late tonight
     for MIZ037-043-050-056-064-071.
MARINE...Small Craft Advisory from noon today to 6 AM EDT Thursday for
     LMZ844>849.

&&

$$

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