777
FXUS63 KDTX 171103
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
703 AM EDT Thu Jul 17 2025

.KEY MESSAGES...

- Cooler and less humid air filters in today 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.

&&

.AVIATION...

A cold front sweeps the rest of the way across SE Mi early this
morning followed by MVFR and brief IFR ceiling with W-NW wind
gusting around 25 knots. Ceiling gradually improves into low end VFR
this afternoon while wind direction veers toward the north late in
the day. Further veering toward NE occurs this evening as high
pressure builds in from the Midwest, although an associated clearing
trend will be slow to progress due to Lake Huron influence. The
decreasing cloud trend gains traction as surface and boundary layer
wind veer even more to the east toward sunrise.

For DTW/D21 Convection... Thunderstorms are not in the forecast
today and tonight.

THRESHOLD PROBABILITIES...

* High for ceiling 5000 ft or less today and this evening. Moderate
  late tonight.

&&

.PREV DISCUSSION...
Issued at 348 AM EDT Thu Jul 17 2025

DISCUSSION...

Morning surface observations reveal the progression of the
approaching cold front which is now closing in on Lansing (as of
07Z). Muted upstream precipitation response, in the wake of the
boundary, lends further confidence in lowering PoPs locally today as
it translates across Southeast Michigan through the next 6 hours.
00Z global models have fallen in-line with prior CAMs in limiting
QPF for the Southeast Michigan with the FROPA. Forecast soundings
indicate column winds veering from SW to W which has led to steady
drying, plus warming within the 800-700 mb layer leads to a capping
inversion. This scenario pertains to most of the forecast area, but
closer to the Tri-Cities and Thumb regions, instability lingers a
bit longer. Paired with closer proximity to the surface low (and
MCV), left some Chance PoPs until mid-morning, but residual activity
should largely be thunderless. Post-frontal airmass supports some
healthy coverage of stratocumulus through the diurnal cycle.
Becoming breezier with time as flow veers toward the northwest
amidst sub-700 mb anticyclonic flow tracing back to northwest
Ontario. This produces a surface thermal gradient of about 10F
between highs over Metro Detroit (lower 80s) and the Tri-Cities
(lower 70s). Seasonably cool overnight with lows dipping into the
50s, beyond Metro Detroit.

Surface high pressure passes over Lower Michigan Friday, on its way
toward the eastern Great Lakes. Base of the thermal trough axis
extends its gradient over the region, marked by a brief intrusion of
850 mb temperatures in the single digits (Celsius) during the
morning hours. Lower column warming ensues as the day progresses,
attributed to the shift toward a weak return flow pattern which
transitions to light southerly gradient winds. Still subjectively
pleasant for mid-July standards Friday with highs in the 70s and
dewpoints in the 50s, perhaps lower 60s closer to the MI/OH border.

Dynamic zonal flow aloft, marked by 110+ knot jet streak at 250 mb,
centers over the northern Great Lakes Saturday. Potential exists for
periods of showers and storms Saturday with multiple features of
note poised to impact the region. An MCS rolls across The Plains,
clipping southern Lower as it anchors to a basal shortwave trough
Friday night into Saturday. Meanwhile, a shall cyclonic circulation
drifts east into northern Lower offering weaker precipitation
intensity. MLCAPE values are expected to rise locally as the ThetaE
plume gets shoved downstream, across Lake Michigan. Moisture
advection will also be reinforced by a low-level shift to southwest
flow. This lends a more favorable convective environment should
glancing forcing materialize. Timing details still need to be worked
out, especially as it relates to the southward redirection of height
falls along the MCS. Becoming drier and cooler again Sunday as the
longwave trough departs, but ridge amplification over north-central
CONUS builds in early next week. Anticyclone over The Southeast
builds into the Lower Mississippi Valley mid-week as +590 dam
geopotential heights extend into southern Lower. Ridge running
shortwave features offer additional thunderstorm chances while
temperatures trend back to 90F.

MARINE...

Compact low pressure tracks east across Saginaw Bay and central Lake
Huron early this morning bringing scattered thunderstorms. Gusty
west wind will overspread western Lake Erie into Lake St. Clair this
morning and a Small Craft Advisory is in effect. The cold front then
pushes across the area through the rest of the morning with gusty
northwest wind ensuing in its wake. This will reach the 20 to 25 kt
range during the late morning and afternoon with waves in excess of
4 feet developing over parts of Lake Huron. These waves are likely
to impact parts of the nearshore around the tip of the Thumb and a
Small Craft Advisory is in effect there as well. Winds then
gradually veer around to the north-northeast this evening while
decreasing to 15 knots or less. Broad high pressure builds into the
area on Friday, promoting light and variable winds. Southerly wind
arrives on Saturday to bring the next humid and unstable air mass
back into the region.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

MI...Beach Hazards Statement through this evening for MIZ049.

Lake Huron...Small Craft Advisory from noon today to midnight EDT tonight for
     LHZ421-441.

     Small Craft Advisory from 4 PM this afternoon to midnight EDT
     tonight for LHZ442-443.

Lake St Clair...Small Craft Advisory until noon EDT today for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory until noon EDT today for LEZ444.

&&

$$

AVIATION.....BT
DISCUSSION...KGK
MARINE.......TF


You can obtain your latest National Weather Service forecasts online
at www.weather.gov/detroit.