Expert Forecast Opinion

555
FXUS63 KDTX 272315
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
715 PM EDT Sun Jul 27 2025

.KEY MESSAGES...

- Hot and humid conditions prevail Monday and Tuesday. High
temperatures reach the lower 90s with peak heat index near 100 each
day.

- A stray thunderstorm is possible Monday afternoon before gradually
increasing potential for greater coverage Tuesday and Wednesday.

- Dry weather hightlighted by cooler temperatures and much lower
humidity arrives for the late week period into next weekend.

&&

.AVIATION...

Quiet aviation conditions will continue across the airspace through
a good portion of the upcoming forecast period. The limited coverage
diurnal cumulus will dissipate quickly with the cessation of surface
heating. Mixing through the day has dried the surface layer a touch.
However, there is certainly enough moisture availability to support
MVFR fog formation overnight - but it will quickly fade within 2 to
3 hours of sunrise. Otherwise, limited cumulus development will
occur through the early afternoon, as high pressure and associated
subsidence suppress cloud development. By late afternoon, the
boundary layer will become more favorable for greater cumulus
development. Additionally, the hot airmass, under light wind
conditions, will drive rather deep and aggressive lake breeze
structures that may be sufficiently deep to support thunderstorm
development.

For DTW/D21 Convection... isolated thunderstorm development is
possible late Monday afternoon into the evening - especially along
lake breeze boundaries.

THRESHOLD PROBABILITIES...

* Low for thunderstorms Monday afternoon.

&&

.PREV DISCUSSION...
Issued at 358 PM EDT Sun Jul 27 2025

DISCUSSION...

Hot and humid conditions take center stage in the SE Mi forecast for
the next few days highlighted by peak heat index near the Advisory
threshold Monday afternoon. The muggy air is accompanied by dry
weather, although thunderstorms occur nearby enough to monitor in
case any strays can reach the area or develop overhead. Storm
potential gradually increases Tuesday as a Midwest cold front
approaches and then moves through Lower Mi early Wednesday.

This afternoon, high pressure over Lower Mi is weak but sufficient
for dry weather and clouds limited to shallow cumulus that mixed
from morning stratus. Surface Td has also dropped slightly in
response to the boundary layer mixing process to hold heat index in
the upper 90s most locations. A short wave ridge at 500 mb adds to
the larger scale subsidence that is maintaining a corridor of mid
level dry air to further suppress convective potential in the
otherwise warm and humid air across the region. Consensus of 27/12Z
model data shows this mid level dry air holding ground against
advancement of upstream convection late tonight and Monday morning.
Surface based storms in the Midwest this afternoon tend to follow
the mean flow into the northern Great Lakes and toward the northern
Ontario frontal zone. Nocturnal development with similar origin is
expected to follow the best low level inflow SE along the
instability gradient. Both of these scenarios leave just patchy mid
and high debris clouds over Lower Mi until Monday afternoon. An
isolated storm then becomes possible mid to late day as 500 mb flow
becomes less subsident while veering slightly into Monday evening.
The clouds and convective potential, combined with a lingering Td
mixing tendency, support of peak heat index just briefly touching
Heat Advisory criteria Monday afternoon.

Prospects improve for persistence of both surface based and
nocturnal convection from the Midwest into the Great Lakes later
Monday night into Tuesday. Northern Ontario low pressure is
projected to pull the cold front to near a line from eastern upper
Mi into the central Plains Monday night. While the front is still to
the west, the instability gradient also moves closer to provide a
runway for a potential MCS track into Lower Mi. There is the usual
wide range of timing/location/intensity differences, however the
general theme is fairly solid in model solutions for this type of
convective scenario. The front then reloads with a very similar MCS
scenario possible Tuesday night while moving through Lower Mi into
Wednesday morning. Longer range model solutions then remain on track
for a substantial air mass transition to cooler and less humid
conditions for the late week period.

MARINE...

High pressure overhead ensures dry weather and light winds across
the marine areas. Variable wind direction is observed in the light
flow regime due to lake breeze development, but will become
southwest by Monday morning as the high drifts east. An active storm
track holds in place with a few more shortwaves rippling along the
ridge Monday and Tuesday to keep shower and thunderstorm chances in
the forecast. Outflow from upstream MCS activity affords low
confidence in wind direction through mid-week, although the pattern
will favor a northerly direction and continued light wind speeds. By
mid-week, a more pronounced cold front drops in from Ontario which
shifts winds more permanently to the north. High pressure then
slides in from Canada to ensure a drier forecast late week into the
weekend.

&&

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

$$

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


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