940
FXUS63 KDTX 251804
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
204 PM EDT Tue Jun 25 2024

.KEY MESSAGES...

- Breezy southwest to west wind persists through this afternoon with
  gusts of around 30 mph.

- There is a chance for showers and possibly a thunderstorm
  Wednesday with severe weather not expected.

- Cooler and less humid air moves back into the area by Wednesday
  night and lasts through Thursday.

- The next chance of showers and thunderstorms arrives Friday night
  into Saturday.

&&

.AVIATION...

Strong subsidence in the wake of the morning convection has cleared
most of the cloud cover in the lowest 10 kft leading to primarily
VFR, as well as gusty southwest winds, that will both persist
through the afternoon. A SCT to BKN cloud deck based mainly between
3 and 5 kft may develop this afternoon as mid-level moisture
attempts to work back in. Additional convection appears unlikely
this evening into tonight even as a weak cold front sinks south into
the area. There will be a chance for vsby reduction in fog/mist late
tonight into early Wednesday morning, especially south of M-59, as
winds become weak and moisture pools along the front - however
confidence is too low to include at this time given expectation for
a good amount of mid and high clouds. Chances for showers and
possibly a thunderstorm then increase mid morning tomorrow as the
stalled front helps trigger scattered convection in the area.

For DTW/D21 Convection...Thunderstorms are not likely this evening
into tonight. Chances for showers and possibly a few rumbles of
thunder then increase after 14Z Wednesday.

DTW THRESHOLD PROBABILITIES...

* Medium for ceilings aob 5kft this evening, low overnight, then
  medium Wednesday morning.

* Low for thunderstorms through Wednesday.

&&

.PREV DISCUSSION...
Issued at 1028 AM EDT Tue Jun 25 2024

UPDATE...

A few adjustments to the forecast with this morning update. Adjusted
PoPs accordingly with the progression of the MCS and the trailing
stratiform rainfall. Rain has ended across the Tr-Cities and Thumb
with a wake low producing gusty winds up to around 40 mph over land
areas. These winds have been much stronger over Saginaw Bay. Will
continue to monitor these wake low winds that may spread southward
through the remainder of the morning behind the trail edge of
rainfall. Have bumped up wind gusts up slightly through the morning
hours to account for this. The severe thunderstorm threat has also
ended from the morning MCS and have cancelled the Severe Thunderstorm
Watch.

PREV DISCUSSION...
Issued at 358 AM EDT Tue Jun 25 2024

DISCUSSION...

Multiple convective clusters blossomed across the upper Midwest
since sunset and are the forecast focus for Lower MI through this
morning. The northern WI cluster became dominant in a location where
mesoscale low pressure focused strong acceleration of the low level
jet. Aggressive transport of moisture and instability now continues
along and ahead of the southward extending surface warm front that
marks the instability axis attracting persistence the existing storm
complex or new storm development through the early morning cycle of
nocturnal/elevated instability generation. This presents both a
severe storm and excessive rainfall hazard across central and
southern Lower MI this morning.

There is room for additional upscale growth of the main northern WI
convective cluster into full MCS organization which gives it a
chance to overcome instability limitations with eastward extent into
SE Lower Mi. Zonal 50 kt flow at 500 mb is a marker for enough shear
to maintain balance long enough for sufficient strengthening of the
low level cold pool and rear inflow. The mesoscale forcing then
becomes strong enough for the system to remain surface based as the
larger scale instability axis leans into western Lower MI toward
sunrise where the strongest and most organized part of the system is
favored to track. We also have to assume the eastern flank will be
capable of severe intensity until it is proven the sharp eastward
instability gradient can take a toll on the MCS strength as it
tracks toward the Tri Cities and Thumb shortly after sunrise, and
farther toward the I69 corridor by mid morning. A more typical
weakening trend then continues late morning due to both weakening of
the low level jet and veering/weakening inflow. This leaves more of
a heavy rainfall threat in place for the Detroit metro area
southward until the remains of the system exit into Ontario and Ohio
by early afternoon.

Conditions across SE MI will be stabilized considerably this
afternoon, first by rain-cooled boundary layer air and then by warm
temperatures aloft for the remainder of the day. A substantial west
to east outflow boundary ends up south of the Ohio border which is
later joined by the trailing surface trough that forces the
instability axis into a similar west to east configuration by this
evening. Additional surface based storms will be slow to develop
along the hybrid outflow/prefrontal trough due to the capping aloft
and little to no additional forcing on the heels of the early day
system. Instead, another round of low level jet forced thunderstorm
complexes are likely to initiate upstream where another round of
surface low pressure is projected to form. This wave runs eastward
along the surface trough keeping showers and storms mainly along and
south of the IN/OH border until merging with the next northern stream
mid level short wave. Showers and weaker storms spread back into SE
MI Wednesday morning until the primary cold front sweeps through in
the afternoon.

Cooler and less humid air follows the Wednesday front which brings
high temperatures back down into the 70s across the area by
Thursday. Broad high pressure settles over the region Thursday into
Friday but is kept moving by the large scale upper air pattern that
maintains a progressive character through next weekend.

MARINE...

Remnant convection from WI/western Great Lakes works into the
central Great Lakes this morning bringing the potential for a few
strong/severe wind gusts within thunderstorm activity. These showers
and storms clear the area by midday though a slow moving cold front
dropping through the area will offer another window for showers and
storms to redevelop latter part of today. These chances are mainly
focused over the southern Great Lakes. Breezy SW conditions in
advance of said front have led to the need for small craft
advisories for all nearshore waters through much of the day today.
An upper level trough settles into the Great Lakes Wednesday through
late week bringing seasonably cooler conditions as well as more
unsettled weather.

HYDROLOGY...

A complex of thunderstorms moves north to south across Lower
Michigan this morning. Locally flooding rainfall is possible from
this system as it produces widespread totals near 0.5 inch during
the morning and isolated totals of 1 to 2 inches before exiting the
area this afternoon.

After a break during the afternoon, a second round of storms becomes
possible tonight into Wednesday morning. The latest storm trends
still support the best thunderstorm potential along and south of I94
where additional totals of 0.25 to 0.50 inch are likely and isolated
totals up to 1 inch are possible until the pattern exits the area by
Wednesday afternoon.

The potential for flooding in each event is greater where repeated
rounds of storms occur over the same area making ponding of water on
roads and in prone low lying areas likely. The Tuesday and Wednesday
activity collectively could lead to a brief response in the level of
streams and rivers across the area through mid week.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...Small Craft Advisory until 10 PM EDT this evening for LHZ421-422-
     441>443.

Lake St Clair...Small Craft Advisory until 4 PM EDT this afternoon for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory until 4 PM EDT this afternoon for LEZ444.

&&

$$

AVIATION.....TF
UPDATE.......AA
DISCUSSION...BT
MARINE.......KDK
HYDROLOGY....BT


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