906
FXUS63 KDTX 171910
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
310 PM EDT Tue Jun 17 2025

.KEY MESSAGES...

- Hot and humid through mid-week.

- Small chances for showers and thunderstorms this evening into
  Wednesday morning.

- Slight to Enhanced Risk for severe weather Wednesday afternoon
  into the evening. All hazards are in play including damaging
  winds, large hail, heavy rain and a few tornadoes will be
  possible.

- Storm chances Friday into Saturday. Even hotter and humid
  conditions over the weekend as temperatures push 90 degrees
  and above.

&&

.DISCUSSION...

Morning warm frontal passage has resulted in a hot, muggy day as
southerly winds have advected in upper 60/lower 70 dewpoints as high
make a run for the upper 80s. Trailing cold front from the parent
low center exiting eastern Superior sags into southern MI over the
remainder of the afternoon-evening pushing into resident a 1000-
1500J/kg of SBCAPE (per RAP analysis). While CAMs remain muted on
any convective initiation due to diurnal mixing drying the boundary
layer, they have started trending towards at least widely scattered
development along the front this evening. Given the instability in
place, running forecast will hold with entry level chance PoPs (25%)
for the area. With wind profiles largely unidirectional and aob
20kts, shear is minimal keeping the mode of any convection as pulse.
Given the favored mode combined with forecast soundings still
depicted a well mixed near surface (inverted V), an isolated
strong/damaging wind gust is possible under the more robust
updrafts.

Today`s cold front stalls out overnight more-or-less bisecting the
CWA (looking to be near M-59) and becomes the focal point for the
advertised active weather Wednesday. Potent shortwave trough
currently generating severe convection over the central Plains lifts
towards the central Great Lakes Wednesday morning pushing our
stalled boundary back north in response. Some scattered showers
along the warm conveyor accompany the front as it lifts north
through the morning hours. The majority of the 12Z model suite
generally in agreement this warm front is forced up to somewhere
between I-69 and the northernmost Thumb/Saginaw Valley by Wednesday
afternoon. While some uncertainty exists in exactly how much
convection develops during the afternoon along the frontal boundary-
owing to the strength of advection building instability over SE MI,
CAMs do advertise at least widely scattered convection (if not more
depending on the model) either initiating along the front or
tracking in from western MI by early afternoon (~16-18Z). This
activity then works across the northern CWA over the course of the
afternoon. Shear in the frontal zone looking to be around 35-40kts
promoting organized updrafts for anything that does fire. As is
typical with warm fronts, concern is that any stronger cell that
crosses or tracks along the boundary will be in a favorable
environment to generate a tornado. While hodos in the frontal zone
aren`t particularly elongated, backed flow supports modest low level
curvature and 0-1km SRH values between 100-150. Exact placement of
the front will determine the more precise threat area but for now
anywhere from the I-69 corridor-north is in play.

The main `show` for severe potential comes Wednesday evening when
the shortwave arrives over the western/central Great Lakes.
Confidence is increasing in an earlier arrival window compared to
the past few day`s model runs with a line of storms crossing SE MI
between ~20-02Z fed by a 40-50+kt LLJ. This line originates from
northern IL/IN where convective initiation occurs sometime around
midday/early afternoon before undergoing upscale growth as it tracks
towards SE MI. A few caveats that will have a large impact on both
the precise timing and nature of the line are when/where exactly
storms fire over IL. The environment over the southern Great Lakes
is uncapped meaning once storms develop, there isn`t much inhibiting
upscale growth as the LLJ provides ample shear/organization (as well
as elongating hodographs, especially in the lowest levels). Earlier
initiation, closer to noon, would support a higher likelihood of a
mature cold pool formation and a QLCS nature by the time the line
arrives over SE MI. This outcome would result in only limited severe
hail potential with strong wind gusts being the primary hazard and
QLCS spin-up tornadoes within the line as the secondary threat.
Conversely later initiation, or initiation more over northern IN
instead, would lead to a less mature complex and allows semi-
discrete storms within a still developing line/QLCS. This outcome
has all threats on the table as semi-discrete cells would be capable
of large hail (1"+) in addition to the damaging winds/tornado
hazards. Additionally, there has been some signal amongst a subset
of models, mainly ones that favor IL initiation closer to noon, for
convection to outpace the shortwave. This would result in a slight
weakening and slowing of the line as it reaches the westernmost
portion of the area before being reinvigorated while crossing SE MI
by the arrival of the wave/LLJ and its accompanying enhanced
instability. Regardless of the aforementioned scenarios, area of
greatest concern for strongest winds, and potential QLCS tornadoes
extension, is along/south of M-59. These southern areas currently
are favored to see the core of the LLJ crossing overhead (which
could peak at 60kts). In addition to the severe threat with
Wednesday`s storms, heavy rain is likely- see the Hydrology section
for more information.

Trailing showers taper off by Thursday morning as low pressure
rapidly slides into Quebec. Late week and weekend pattern
characterized by continued hot, humid conditions with multiple storm
chances. Large upper ridging is expected to develop across the
central/eastern CONUS by Friday that then holds in place through at
least the beginning of next work week. Long range guidance continues
to highlight a high potential for highs reaching into the 90s,
overnight lows only in the upper 60s/70s, and surface dewpoints
likewise in the upper 60s/low 70s. Ridge running MCS`s in play for
the weekend though its too far out to determine their exact track.

&&

.MARINE...

A low pressure system lifting across eastern Ontario has draped a
warm sector over the central Great Lakes resulting in southwesterly
winds. Speeds have generally held below 15 knots with sub-25 knot
gusts, thus will maintain headline-free status through the rest of
the day and overnight. A few showers and thunderstorms are possible
late today and into the overnight hours. A stronger low lifts into
the region Wednesday providing several rounds of thunderstorms, some
of which may be severe. Increasing likelihood that these storms
could necessitate Special Marine Warnings for locally higher winds
and waves, in addition to isolated large hail potential. Active
pattern could continue through the end of the week as the system`s
cold front stalls across the Great Lakes Thursday followed by
another weak low heading into the weekend.

&&

.HYDROLOGY...

Gulf moisture feed pushes PW values near daily records (at or above
1.75") and offers heavy rain/flooding potential with storms
Wednesday and Wednesday evening. With this very warm/humid airmass,
forecast soundings show warm cloud depths of 12-15kft throughout the
day increasing precip efficiency with both any preceding
showers/storms along the warm front daytime Wednesday as well as
convection with the low itself late day. Model guidance continues to
show some support for training convection during the day along the
warm frontal boundary before the arrival of the low which could
boost overall QPF. Average rainfall totals over the course of
Wednesday will be 0.75-1.50 inches with locally higher totals (1.5-
3") likely. Stronger storms and/or repeated rounds of thunderstorms
will be capable of a quick 1-2 inches in a 1-3 hour window. This
brings with it flooding concerns, especially if higher intensity
rainfall impacts urban areas.

&&

.PREV DISCUSSION...
Issued at 148 PM EDT Tue Jun 17 2025

AVIATION...

Expanding coverage of lower VFR cumulus continues this afternoon as
moderate SW flow brings warm and increasingly humid air into the
Great Lakes. This occurs ahead of low pressure in northern Ontario
that also pulls a cold front into Lower Mi which is expected to
stall near the FNT to MBS area tonight. Isolated thunderstorm
potential lingers late this afternoon and early evening toward the
PTK to DTW area then shifts toward FNT and MBS along and north of
the cold front later tonight. Borderline MVFR stratus is likely
along and near the stalled front and also in the warm sector late
tonight and Wednesday morning.

For DTW/D21 Convection...There is a slight chance (~25%) for an
isolated thunderstorm favored in the evening hours.

THRESHOLD PROBABILITIES...

* Moderate for ceiling aob 5 kft this afternoon through Wednesday
  morning.

* Low for thunderstorms late today and this evening.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...None.
Lake St Clair...None.
Michigan waters of Lake Erie...None.
&&

$$

DISCUSSION...KDK
MARINE.......KGK
HYDROLOGY....AA/KDK
AVIATION.....BT


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at www.weather.gov/detroit.