422
FXUS63 KDTX 211057
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
657 AM EDT Thu Aug 21 2025

.KEY MESSAGES...

- Seasonable temperatures and dry weather expected to close out the
  work week.

- Chance of showers and thunderstorms Saturday and Saturday night as
  a cold front tracks across the area.

- Below normal temperatures expected post-front Sunday through
  Wednesday with highs in the upper 60s to 70s.

&&

.AVIATION...

A wide range of ceiling conditions are observed early this morning
as cool NE flow continues off Lakes Huron and Erie. A few hours of
mainly MVFR ceiling occurs as the plentiful boundary layer moisture
reacts to the beginning of daytime heating. Bases build up into low
end VFR and then scatter out this afternoon heading into a mostly
clear evening. Still plentiful open sky later tonight becomes
favorable for areas of fog as surface high pressure settles from the
upper Midwest and northern Great Lakes over SE Mi toward sunrise
Friday.

For DTW/D21 Convection... No thunderstorms today and tonight.

THRESHOLD PROBABILITIES...

* High for ceiling aob 5000 feet this morning.

&&

.PREV DISCUSSION...
Issued at 352 AM EDT Thu Aug 21 2025

DISCUSSION...

Northeast flow holds steady this morning, with the main forecast
concern of the day being trends in cloud cover. Loss of synoptic
moisture should trend toward a more scattered to broken deck of
stratocumulus off of Lake Huron by this afternoon, but not banking
on full clearing until late this evening when wind speeds subside
and shift away from the lake. Did drop temperatures by 2-3 degrees
provided the marked increase in sky cover grids and trends noted
from yesterday. High pressure governs conditions through the end of
the work week with overall benign weather expected and temperatures
returning to near normal Friday and Saturday.

Disorganized area of low pressure has already started to develop
over Saskatchewan, with a defined upper low advancing eastward
across Alberta. Should see rapid maturation of the surface low
today, which will then release eastward on Friday toward Hudson Bay
this weekend. Height falls begin across lower Michigan Friday night,
followed by the arrival of a cold front on Saturday. Timing of the
front is still quite variable in the model data, ranging anywhere
from mid-day (21.00z GFS) to late evening (21.00z NAM). Focus around
the diurnal peak provides a window of opportunity for convection
along the front, although models have really only been able to
generate a narrow/weak axis of instability (< 1000 J/kg) where
moisture convergence exists ahead of the front. Deep convection will
further be complicated by the influx of a dry slot aloft,
establishing at least weak capping throughout the day. Any updrafts
that can overcome the thermodynamic limitations could take advantage
of deep layer shear (45-50 knot westerlies) in the basal portion of
the upper trough, supporting conditional potential for isolated
organized convection.

Once the front comes through, PW values drop quickly below 1" and
850mb temperatures drop into the single digits by Sunday morning.
This signifies the transition to an extended stretch of below normal
temperatures that settle in through at least middle of next week.
Both mid-level heights and low-mid level temperature fields fall
into the 1st percentile per NAEFS climatology as daytime highs are
capped in the upper 60s to 70s for the early half of the week. These
cool, upper low patterns are often associated with a strong moisture
response off of the Great Lakes to support stratocumulus and
possibly diurnal shower development.

MARINE...

High pressure drifts over the region through Friday maintaining
generally lighter winds (aob 15kts) and dry conditions. Broad low
pressure system tracking over northern Ontario drags a cold front
across the region late Friday night-Saturday bringing the next
chances for showers and thunderstorms. An upper trough then settles
over the Great Lakes for the rest of the weekend into early next
week allowing a much cooler, fall-like airmass to sink south.
Strengthening cold advection with this airmass brings breezy
conditions as west/northwest winds reach 15-25kts. Some periods
where gusts approach or exceed 30kts are likely as well. Cooler
weather brings lake effect shower and waterspout chances through
that timeframe.

&&

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

$$

AVIATION.....BT
DISCUSSION...MV
MARINE.......KDK


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