630
FXUS63 KDTX 182236
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
636 PM EDT Fri Jul 18 2025

.KEY MESSAGES...

- There is a likely (55-70%) chance for showers with embedded
thunderstorms tomorrow afternoon and evening. Some isolated to
scattered severe thunderstorm development will be possible.

- The main hazards with any severe thunderstorm development will be
damaging winds gusts of 60+ mph. Secondary hazards will be large
hail to an inch and/or isolated tornadoes.

- Dry conditions Sunday and Monday.

&&

.AVIATION...

Subtle moisture convergence around metro resulted in some diurnal cu
this afternoon, which will erode with the loss of daytime heating
this evening. Skies across the remainder of the terminals have been
clear as high pressure and dry ambient air dominates the eastern
Great Lakes. Lingering high pressure will sustain light winds
through the night with just a few high clouds streaming across the
region from the west.

For DTW/D21 Convection...The development of moderate instability
Saturday afternoon and evening combined with a couple frontal
boundaries and the potential for mid level short waves will provide
a good chance for late afternoon and evening convection on Saturday.

THRESHOLD PROBABILITIES...

* Medium for ceilings at or below 5000-ft Saturday afternoon and
  evening.

* Medium for thunderstorms late Saturday afternoon and evening.

&&

.PREV DISCUSSION...
Issued at 300 PM EDT Fri Jul 18 2025

DISCUSSION...

Expansion of high pressure in the wake of a cold front has produced
mostly sunny to partly cloudy skies with temperature highs holding
in the 70s. The remainder of the evening and overnight hours will
remain dry, noting the very low chances for elevated showers or a
thunderstorm favored through the Tri-Cities and northern Thumb.

Convective evolution across SE MI remains uncertain through tomorrow
afternoon and evening, however, the kinematics warrant chances to
see organized convection which includes the possibility for isolated
to scattered strong to severe thunderstorm development. Attention
will initially be focused across the northern and central Plains into
Minnesota to Iowa late tonight and overnight, where a strengthening
llj will allow for the advection of Gulf moisture to feed and sustain
an mcs along the nose of the jet and along/north of a warm front.
Forward propagating vectors point in the direction of the southern
Great Lakes, however, displacement of the CAPE gradient well south of
the Great Lakes can act to displace the mcs farther south relative
to model projections. This scenario would keep the bulk of this
initial activity confined to the Ohio Valley or locations south.

If sustainment  of this mcs is realized while favoring eastward
trajectories, portions of southern Michigan will have chances to get
clipped by organized convection starting in the afternoon hours. The
complex would elongate hodographs through the mid levels with 1-6km
bulk shear vectors reaching 30-35 knots. Storm relative hodographs
show uniform shear in this scenario with long and straight 1-3km
segments, good for storm organization and possibly some transient
supercell structure, but the weak 0-1km and 3-6km preclude strong
mentions of tornadogenesis with limited vertical vorticity
maintenance respectively. This would most likely lead to the
evolution of linear bowing segment owing the stronger and linear
wind profile in the mid-levels, bringing potential for strong wind
gusts.

Dissipation and/or southern trajectory of the MCS still warrants
chances for shower and thunderstorm development across all of SE MI,
as there would still be a window in the afternoon for theta-e rich
air to expand across the cwa with southerly flow ahead of the
system. There will be uncertainties surrounding moisture
quality/cloud cover and thus cape density in this scenario which
will have impacts on severe weather chances and coverage, but overall
an outflow boundary or organization ahead of a cold front across
northern Michigan with afternoon heating will likely spark some ci
through the afternoon and evening hours. In this instance, kinematics
remain strong, supporting organized convection chances. Storm mode
would be less certain in this scenario, ranging from cellular to
multi-cell, possibly transitioning to some more organized bowing
linear segments. Damaging wind gusts would remain possible with all
thunderstorms, with this thesis further strengthened noting strong
dcape values and steep lllr. Secondary hazards would be large hail
under structured updrafts and a possible tornado, noting better
curvature to SR-hodo in the mid-levels and slight elongation to low-
level segment around the Tri-cities and Thumb. SWODY2 places SE MI
under a slight risk for severe weather.

The cold front sweeps through late tomorrow night into early Sunday
morning where lingering showers or storms will be possible, but
otherwise high pressure builds in in the wake of the front, bringing
a period of dry weather through the early week. Once high pressure
departs east into the Atlantic, return flow will draw hotter
conditions back to SE MI with ridging up to 594dam setting up
through the Great Lakes. This will bring the chance to see
temperature highs return into the 90s Wed-Thu. Periodic shortwaves
rounding the ridge will bring chances for showers and thunderstorms
by the mid to late week period.

MARINE...

High pressure maintains dry and favorable marine conditions through
the evening with light and variable wind gradually organizing out of
the south late. South flow increases to around 10 kt on Saturday
with a warm front lifting across the area. This will usher in a
muggy and unstable air mass with increasing probability for showers
and thunderstorms during the latter half of the day as low pressure
works into the central Great Lakes. Wind speeds and wave heights
will hold below Small Craft Advisory criteria but scattered severe
storms will be capable of producing gusts in excess of 40 kt, hail,
and waterspouts. The cold front clears the area Sunday morning with
drier conditions and moderate north wind to wrap up the weekend.
High pressure passing to the north causes light wind to veer to
easterly on Monday. The next chance of thunderstorms looks to hold
off until Tuesday night into Wednesday along the next warm front.

HYDROLOGY...

Scattered to possibly numerous showers and embedded thunderstorms
will fill in across SE MI tomorrow afternoon and evening. Basin
averaged rainfall totals will range between a quarter-inch to a half-
inch, however, any strong thunderstorm will be capable of quickly
producing localized rainfall totals between 1 to 2 inches. Given
faster storm motions, overall flooding concerns remain low, however,
highly localized flooding remains possible across urban areas and
low-lying flood prone locations.

&&

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

$$

AVIATION.....SC
DISCUSSION...AM
MARINE.......TF
HYDROLOGY....AM


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