539
FXUS63 KDTX 171910
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
310 PM EDT Thu Jul 17 2025

.KEY MESSAGES...

- Cooler and less humid air filters in through Friday.

- Periods of showers and storms are possible Saturday with
temperatures climbing a few degrees toward seasonal normals.

- Becoming drier and cooler again Sunday, after a cold front drops
south.

&&

.DISCUSSION...

Moist near surface conditions are persisting across Southeast
Michigan this afternoon evidenced by widespread stratus ceilings at
2.0 kft agl. Satellite imagery supports a rather thick cloud deck
outside of the downsloping area in the Saginaw Valley. Suspect it is
in this area that clearing will begin as daytime heating wanes. The
southern forecast area will likely be a different story as some
model data supports keeping moisture in place. In fact, models
suggest some additional low level moisture advection from the east
overnight. For the grids did continue optimistic sky trends in the
north, but did hand edit a more pessimistic overcast forecast in the
south late tonight and a good part of Friday. Lows tonight will
range from the lower 50s north to lower 60s in the Detroit heat
island. Heat indices Friday are expected to be in the middle to
upper 70s.

On Saturday, the next wave of low pressure will be driven by right
entrance region dynamics of a fairly zonal upper level jet streak.
Plan view progs of moisture show a surface warm frontal surge
occuring between 12-15Z with 900-700mb thetae return during the mid
to late afternoon hours. Respectively steep lapse rates are expected
above 12.0 kft which could yield MUCAPEs/SCAPEs up to 3000 J/kg.
Given the larger scale forcing both with the jet forcing aloft and
warm advection, difficult to pin down any short time windows for
precipitation. Rather, looks like there will be chances throughout
the day and will need to account for the timing and evolution of
upstream MCS activity. Will take destabilization during the
afternoon to sustain any deep convection and it is late in the day
that 0-6km bulk shear is forecasted to increase between 40 to 50
knots. At this point, Swody3 has Southeast Michigan in a General
Thunderstorm designation.

1000-500mb geopotential height rises over the Great Lakes will allow
for surface high pressure across the region Sunday through Tuesday.
Forecast soundings suggest mid-upper level dry air during the time
period with subsidence varying between 6.0 and 16.0 kft agl. A very
comfortable period early next week.

&&

.MARINE...

High pressure arrives from the west tonight causing gusty northwest
winds to weaken and veer north to northeast. Small Craft Advisories
remain in effect along the Lake Huron nearshore where 4+ foot waves
will persist through this evening. The high spreads directly
overhead on Friday causing winds to go light and variable. By
Saturday, wind organizes out of the south as the high departs east
and a warm front lifts into the Great Lakes. This will bring the
next round of humid, unstable weather with scattered showers and
storms this weekend. Wind speeds and wave heights will hold below
advisory criteria but may be locally higher in and around
thunderstorms. The cold front clears the area Sunday with moderate
north wind to wrap up the weekend.

&&

.PREV DISCUSSION...
Issued at 130 PM EDT Thu Jul 17 2025

AVIATION...

General trend is for low cloud (sub-5.0 kft) to linger through early
Friday morning as cooler post-frontal flow has activated Lake
Michigan and Lake Huron. There is a low chance for clouds to scatter
this evening, but would be brief as winds veer to the NE and
redirect downstream moisture overhead. High pressure slides across
lower Michigan tonight, which lowers inversion heights and increases
chances for MVFR conditions through 12z Friday. Winds eventually
shift offshore Friday morning as diurnal heating ramps up to result
in a clearing trend that persists through the rest of the TAF
period.

For DTW/D21 Convection... Thunderstorms are not in the forecast
through Friday.

THRESHOLD PROBABILITIES...

* High for ceiling 5000 ft or less today, moderate this evening,
  high between 04z and 12z Friday.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Beach Hazards Statement until midnight EDT tonight for MIZ049.

Lake Huron...Small Craft Advisory until midnight EDT tonight for LHZ421-441>443.

     Small Craft Advisory until 4 PM EDT this afternoon for LHZ422.

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

$$

DISCUSSION...CB
MARINE.......TF
AVIATION.....MV


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at www.weather.gov/detroit.