599
FXUS63 KDTX 181755
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
155 PM EDT Mon Aug 18 2025

.KEY MESSAGES...

- Dry weather today and most of tonight.

- Scattered showers and storms become possible late tonight through
Tuesday evening. Locally heavy rainfall is the primary concern with
this activity.

- Seasonable temperatures and dry weather move in and hold Wednesday
through Friday.

&&

.AVIATION...

A deep low pressure system will organize over northern Wisconsin
today and dig southeastward into Southeast Michigan on Tuesday. A
sharp moisture gradient will precede the low pressure system and
lead to moisture advection tonight. There is a potential period for
showers and thunderstorms at KMBS and KFNT after 08Z tonight, before
chances increase at all taf sites between 13-16Z. Introduced a TEMPO
group for TSRA at the Detroit taf sites. Diurnal MVFR cig heights
this afternoon will lift to VFR. Prevailing VFR is anticipated
tonight. Brief IFR to LIFR conditions will be possible with heavy
rainfall.

For DTW/D21 Convection...Thunderstorm activity is possible after 13Z
Tuesday.

THRESHOLD PROBABILITIES...

* Low for thunderstorms after 13z Tuesday.

&&

.PREV DISCUSSION...
Issued at 403 AM EDT Mon Aug 18 2025

DISCUSSION...

Comfortably cool conditions are in place across all of SE Mi to
start the day as most locations report temperature well down into
the 50s outside of metro Detroit. Some faint indications of lake
clouds off Huron and Saginaw Bay, and not so faint off Erie, since
midnight also emphasize the air mass contrast across the water that
is at peak seasonal warmth. Temperature on land rebounds accordingly
with full sun outside of patchy stratocu early and cirrus throughout
the day leading to guidance highs around 80.

Upstream observations remind us that the next round of showers and
storms is nearby to the west and due into Lower Mi late tonight
through Tuesday. The front stalled in the Ohio valley extends into
the upper Midwest where clusters of convection illustrate the sharp
temperature and moisture contrast still present. The front is
readily available to low pressure developing in the northern Plains
and its low level jet spreading moisture along and ahead of the
frontal zone. The sharpness of the 850-700 mb theta-e ridge also
suggests elevated convection is likely to survive and continue
eastward through the typically hostile daylight hours for elevated
convection. Any loss of coverage and intensity is regained with a
new round of nocturnal moisture transport tonight beginning nearby
in northern and western Lower Mi and progressing across SE Mi late
tonight and early Tuesday. Heavy rainfall potential is best during
this phase of the system in the Great Lakes but still marginal due
to a relatively weak low level jet, the possibility of moisture
disruption from mid MS valley convection, and steady progression of
the larger scale pattern. There is also a surface based convective
component likely by Tuesday afternoon into the evening as the low
level moisture axis moves across Lower Mi followed by the cold
front/occlusion, however storm intensity is expected to be limited
by minimal recovery of instability after the earlier day activity.

Continued occlusion of the surface frontal system, and a boost from
the 500 mb wave, result in secondary low pressure near the Ohio
border and a lingering chance of showers in SE Mi Tuesday evening.
The low pressure system makes a more aggressive move to exit
eastward as the effective frontal passage by Wednesday morning
followed by increasing north wind across Lower Mi that brings in
another round of cooler and less humid air. The 18/00Z model run is
in good agreement on solutions that show the long wave ridge
building back north into central Canada and then leaning eastward
over the Great Lakes during the late week. This is followed by a
larger/stronger Canadian low pressure system set to bring the next
cold front through Lower Mi to start next weekend.

MARINE...

East-northeast winds will be mostly weaker today compared to
yesterday as high pressure retreats and a warm front lifts in from
the Western Great Lakes, allowing waves to diminish further.
However, the exception will be across the northern third of Lake
Huron/near the Straits where channeling of the winds looks to
support gusts of 25 knots to possibly briefly near 30 knots this
afternoon.

Surface low pressure tracking through northern Lower Michigan on
Tuesday looks to be triggering showers and thunderstorms, especially
over northern Lake Huron where southeast winds look to be at least
25 knots, with the potential to reach around 30 knots.

Northeast winds redevelop over all of Lake Huron Tuesday night as
the low tracks to the east, and another round of small craft
advisories are likely as winds look to gust around 25 knots once
again on Wednesday over southern Lake Huron. Surface ridge tracking
through the Central Great Lakes will allow for light winds on
Thursday and Friday however.

&&

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

$$

AVIATION.....CB
DISCUSSION...BT
MARINE.......SF


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