281
FXUS63 KDTX 202357
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
757 PM EDT Thu Aug 20 2026

.KEY MESSAGES...

- Showers and scattered thunderstorms will affect the area Saturday.

- Cooler and breezy conditions arrive Sunday with lingering shower
chances.

&&

.AVIATION...

VFR conditions are expected to prevail through tonight as high
pressure moves through Michigan. A easterly wind component this
evening into tonight will eventually become southerly tomorrow
afternoon while holding between 5-10 knots. Mainly scattered high
clouds tonight with increasing coverage towards tomorrow evening.
Ceilings should remain VFR as increasing scattered mid clouds arrive
mid-day.

D21/DTW Convection... No convection is forecast for the period.

.DTW THRESHOLD PROBABILITIES...

* None.

&&

.PREV DISCUSSION...
Issued at 305 PM EDT Thu Aug 20 2026

DISCUSSION...

Subtle mid level ridging developing over Se Mi tonight is forecast
to drift across the eastern Great Lakes Friday. Associated surface
high pressure and low level anticyclonic flow will hold across the
eastern Great Lakes through the day Friday. The influence of this
system will maintain dry weather through the next 24 to 36 hours.
Much like today, there will likely be areas of diurnally driven cu
and high based clouds on Friday. Light SSE flow in the boundary
layer and diurnal mixing will support afternoon highs into the low
80s, which has fairly good support within the probabilistic
guidance. While south flow will begin advecting a little more
instability into the region Friday afternoon, model soundings
indicate a strengthening mid level cap through the day which will
prove a formidable limiting factor on convective initiation.

Long wave trough amplification across the Great Lakes Saturday will
result in mid level height falls across Se Mi along with the passage
of a surface low and cold front. A plume of deep layer moisture
advection ahead of this trough late Friday/Friday night will drive
precipitable water values to 1.4 to 1.6 inches. The forced ascent
combined with the resident moisture and diurnal instability will
support a chance of showers/thunderstorms. The model prob space is
suggestive of high chances for rain Saturday, over 80 percent.
Within the probabilistic guidance, median QPF is around a quarter
inch, with a half inch to three quarters inch within the 90th
percentile. The chances for severe weather continue to look limited
(marginal risk/isolated) with SB CAPE values forecast to range from
800 to 1400 J/kg and marginal 0-6km Bulk Shear values of 20-30
knots.

Post frontal northwest flow will drive cooler air across the Great
Lakes in the wake of the front; 850mb temps will drop into the
single digits on Sunday. Steep low level lapse rates the cool air
aloft will contribute to a healthy diurnal cu field on Sunday. This
may support a few showers; the better chances will be across the
thumb given the added moisture flux off Lake Huron. The cool air and
daytime cloud cover will hold high temps in the 70s. Remnant
northwest flow circulating around an eastern Canadian upper low will
sustain seasonally cool temperatures into early next week. A
northern stream short wave will provide the next chance for
showers/thunderstorms during the middle of next week. At this stage
in the forecast there is still ample spread among ensemble members
with respect to timing and potential rainfall amounts.

MARINE...

Surface high pressure lingers over Ontario rest of today and Friday,
maintaining an easterly component to the overall light wind field.
Winds then veer to the south Friday afternoon as a warm front lifts
into the Great Lakes. Dry conditions are expected through the end of
the work week, followed by increasing shower and thunderstorm
chances through the day Saturday as a low and its attendant cold
front sweep across Lower Michigan. This low strengthens as it moves
toward New England, strengthening post-frontal northwest flow and
elevating wind gusts toward 25-30 knots both Sunday and Monday. Peak
gustiness is anticipated Sunday afternoon-evening when cold
advection is strongest. Quieter pattern returns briefly Tuesday
before the next system arrives middle of next week.

&&

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

$$

AVIATION.....AA
DISCUSSION...SC
MARINE.......MV


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at www.weather.gov/detroit.