193
FXUS63 KDTX 232307
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
707 PM EDT Wed Jul 23 2025

.KEY MESSAGES...

- A Heat Advisory remains in effect Thursday as high temperatures
reach the lower to mid 90s with heat index peaking around 102
degrees.

- The potential for thunderstorms continues to increase Thursday
afternoon and especially Thursday evening. The strongest storms will
be capable of 60 mph damaging wind, torrential rainfall, and
localized flooding.

- Continued warm and humid Friday with lingering or renewed
shower/non-severe thunderstorm activity, particularly toward the
southern Michigan border.

- Additional rounds of showers and thunderstorms are likely for
Saturday and Sunday as well.

&&

.AVIATION...

Return southerly flow is starting to increase across Southern Lower
Michigan early this evening. This flow will usher in a wealth of
near surface moisture. Some of the moisture may manifest in VFR
cloud cover (4-5 kft) by daybreak and through the first half of
Thursday morning. Otherwise, strong surface mixing will commence
toward midday and will tap into quicker flow aloft in advance of an
approaching frontal system - setting the stage for gusty conditions
through the entire afternoon. As the front approaches and
instability peaks, thunderstorm development is expected. Coverage
will be predicated on the quality of deeper instability and the
endurance of lower to mid level dynamic forcing with the approaching
upper wave and the settling frontal zone - both of which will be on
the decline. Consequently, coverage of thunderstorms may be somewhat
limited. Main window for development across the Southeast Michigan
airspace is currently in the 19-02z time slot.

For DTW/D21 Convection...convection is expected to develop after 19z
and wash east/southeast across the airspace in the 21-02z window.
Coverage and character of the thunderstorms is still highly in
question. Prospects for thunderstorms in the airspace are relatively
high - but impacts at a single terminal are less confident.

THRESHOLD PROBABILITIES...

* Low for ceilings aob 5kft Thursday morning

* Medium for thunderstorms in the D21 airspace after 20z Thursday

&&

.PREV DISCUSSION...
Issued at 357 PM EDT Wed Jul 23 2025

DISCUSSION...

Mid Atlantic high pressure is reaching back to maintain influence on
weather conditions in the Great Lakes today. A classic late July
afternoon and evening is the result after highs in the mid to upper
80s with low humidity. All of that changes early Thursday as
oppressive mid to upper 70s surface Td washes back over Lower Mi by
afternoon. Upstream observations this afternoon indicate multiple
reports of 80 Td in southern IL, likely agriculturally enhanced but
still impressive. This also supports the Heat Advisory for Thursday
afternoon and evening as high temperatures reach the lower to mid
90s and heat index peaks in the lower 100s.

While inbound heat and humidity are fully supported by observations
today, there are still questions regarding thunderstorm potential
for Thursday. The inbound surface/boundary layer moisture adds
confidence to model projections of a building instability axis
across Lower Mi Tuesday afternoon as HREF mean surface based CAPE
briefly reaches 3000 J/kg. Uncertainty lies in the opposing
influence of capping low to mid level temperatures vs forcing
brought by the current central Plains 500 mb circulation as it moves
into the Great Lakes Thursday afternoon. As it stands at forecast
issuance today, the 23/12Z DTX sounding this morning makes a strong
case for the cap with 11 C at 700 mb and which is forecast to hold
at least through Thursday morning. Satellite observations this
afternoon also make a case for the 500 mb circulation that still
looks well-organized but is forecast to weaken while shearing into
the long wave ridge Thursday afternoon. It may end up just strong
enough to erode the cap more convincingly with northward extent into
central Lower Mi for scattered to numerous storm coverage becoming
more isolated toward metro Detroit. The wind field is also more
favorable for organized convection with northward extent as HREF
offers 500 mb mean wind speed approaching 40 kts and a better bulk
shear profile supporting a damaging wind threat. This may favor the
Marginal Risk more toward the Saginaw valley and northern Thumb
while not ruling out lower coverage toward metro Detroit.

A prefrontal trough is showing up in HREF and regional/global model
solutions as a focusing mechanism for afternoon storms in addition
to the trailing cold front, both of which maintain a concern for
heavy rainfall as an additional hazard through Thursday night. There
are multiple scenarios for heavy rainfall and flooding, but not much
definition on specific threat areas, as the storm environment builds
PW toward 2 inches across the entire region. The potential for
multiple outflows, the surface trough and cold front, all raise
potential for training convective clusters as the pattern slowly
progresses across Lower Mi through Thursday night. The 23/12Z model
consensus then keeps the cold front progressive enough to move south
of the Ohio border during the morning and especially before peak
heating Friday afternoon.

While the surface front settles south of the Ohio border, elevated
portions remain over southern Lower Mi Friday night into the
weekend. There is good consensus in the longer range models on an
active elevated/nocturnal convective signal Friday night and
Saturday night before the front is pulled back north into Lower Mi
during Sunday.

MARINE...

The western edge of mid-Atlantic high pressure continues to govern
Great Lakes conditions today and tonight. Meanwhile, a broad frontal
zone will gradually shift eastward and increase gradient winds
toward 15-20 knots by Thursday afternoon with gusts to 25 knots. SW
flow funneling along Saginaw Bay will have the strongest gust
potential, prompting Small Craft Advisories for the afternoon-
evening. Dry weather is expected through Thursday for most of the
area, with the exception of northern Lake Huron (especially north of
Thunder Bay) which may get clipped by the ongoing thunderstorm
complex over northern Wisconsin late tonight-Thursday morning.
Shower and thunderstorm potential expands across all marine zones by
Thursday afternoon as a hybrid upper level disturbance/cold front
impact the area. Isolated strong to severe thunderstorms,
characterized mainly by wind gusts over 34 knots, will be possible
with the strongest storms. The front settles south toward the
Michigan-Ohio border late Thursday night and stalls, maintaining
shower and storm chances Friday as well. Periods of showers and
thunderstorms remain possible through the weekend as well with a
warm and unstable airmass settling overhead.

HYDROLOGY...

A hot, humid, and moisture rich air mass sets the stage for heavy
rain producing thunderstorms late Thursday afternoon through
Thursday night. There is lingering uncertainty on coverage and
timing that makes it difficult to identify locations having greater
threat. However, any strong to possibly severe thunderstorm will be
capable of a quick 1.5 to 2+ inches of rainfall, which could produce
localized flooding. If storms train over a particular area, more
significant flooding is possible.

Additional showers and thunderstorms are possible Friday, but
rainfall amounts should remain under 1 inch, with the vast majority
of additional activity toward the Ohio border. Higher coverage and
amounts remain possible Saturday and Sunday as yet another upper
level disturbance moves through the region.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Heat Advisory from 11 AM to 8 PM EDT Thursday for MIZ047>049-
     053>055-060>063-068>070-075-076-082-083.

Lake Huron...Small Craft Advisory from noon to 10 PM EDT Thursday for LHZ421-422.

Lake St Clair...None.
Michigan waters of Lake Erie...None.
&&

$$

AVIATION.....Mann
DISCUSSION...BT
MARINE.......MV
HYDROLOGY....BT


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