971
FXUS63 KDTX 272003
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
403 PM EDT Fri Sep 27 2024

.KEY MESSAGES...

- Cloudy and breezy through remainder of today.

- Rain showers associated with the northern fringe of Tropical
  Depression Helene moves into Lower Michigan this evening and
  continue through tomorrow.

- Lower chances for rain persist into Sunday.

&&

.DISCUSSION...

Tropical Depression Helene will continue to weaken and be absorbed
by the cut off the mid-upper level low hanging out over western TN
later today into tonight. The expanse of thicker high clouds
associated with this area of low pressure is extending north through
much of southeast Michigan. This is helping keep temperatures to
around the mid 70s this afternoon. High pressure also resides across
the northern Great Lakes and will contribute to mostly dry
conditions through the rest of the afternoon. The pressure gradient
has tightened between the surface high to the north and the
encroaching height falls from the south resulting in gusty
northeasterly winds. Highest wind potential will be towards southern
Michigan border where gusts to around 35-40 mph being most likely
through the rest of the afternoon with gusts to around 25-35 mph for
the remainder of the CWA.

Deeper moisture begins to creep north of the southern Michigan
border this evening along with better forcing. Regional radar
currently has heaviest precipitation sweeping north of the Ohio
River Valley at press time. Better precipitation chances are after 8
pm this evening across the southern Michigan border as the northern
edge of this precipitation shield arrives while gradually spreading
northward over the next few hours. Moisture will be high with
corridor of PWAT values up to around 1.75 inches, but forcing
overnight will be relatively weak. That will lead to likely showers
up through southern Lower Michigan tonight with QPF amounts up to
0.25 inches possible through 12Z tomorrow. Winds will be gradually
weakening throughout the night as well.

Mid-upper low pressure will remain stalled over TN/KY throughout the
weekend. This will maintain mostly cloudy skies over the region with
persistent weak forcing over south east Michigan Saturday into
Sunday which leads to periods of scattered showers. Highest QPF
totals over the course of the weekend are expected to be within the
quarter inch to half inch range and focused south of I-69. Some
isolated higher amounts to 1 inch or greater will be possible for
areas that see experience repeated rounds of any moderate to briefly
heavy showers that can get going for a brief period during afternoon
peak heating.

Rain chances largely come to an end for Monday as forcing settles
south of the Michigan border and shortwave ridging builds into the
central Great Lakes. Ridging will be brief as a northern stream
trough and cold front swing through the west/central Great Lakes on
Tuesday. This will be the next opportunity for showers and
thunderstorms. Post frontal airmass for Wednesday will bring
temperatures several degrees below average with highs in the 60s.

&&

.MARINE...

A strengthening pressure gradient in response to the approaching
tropical system Helene will continue to support northeast flow
through the remainder of the day and well into tomorrow. The
strongest sustained wind speeds and gust potential will reside
across Lake Erie, which has now been upgraded to a Gale Warning, as
wind gusts to or in excess of 34 knots now remain probable through
the early morning hours. Additionally, rain showers that move in
late tonight and overnight have the potential to pull down stronger
winds aloft to the surface, up to 40 knots.

Otherwise, Small Craft Advisories have been added across the Saginaw
Bay given the favorable northeast fetch which will likely support
gusts up to 25 knots later this evening. Wave heights nearing four
feet eventually follow up tomorrow, which will carry the Small Craft
Advisory well into the day. As the tropical system wanes in
intensity, so will wind and gust potential through Saturday.

&&

.PREV DISCUSSION...
Issued at 122 PM EDT Fri Sep 27 2024

AVIATION...

Remnant moisture from tropical system Helene will continue to bring
an extensive upper-level stratus deck across all of SE MI, with an
eventual sudden lowering of cigs down towards mvfr late tonight and
overnight, coincident with rain showers, as a spoke of moisture
pivots into Michigan. Prior to this, the rapid strengthening of the
pressure gradient in response to the tropical system has and will
continue to sustain winds around 15 knots, with gusts ranging around
25 knots. Periods of IFR will be likely overnight, favored across the
Metro terminals, possibly extending north through PTK-FNT. There is
uncertainty regarding just how far north the low-level moisture will
extend into, with latest guidance holding MVFR cigs just to the
south of MBS through this TAF period.

For DTW/D21 Convection...Thunderstorms are not expected this period.

DTW THRESHOLD PROBABILITIES...

*  Low for ceiling at or below 5000 feet this evening, high
   overnight into Saturday.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Lakeshore Flood Advisory until 10 AM EDT Saturday for MIZ083.

Lake Huron...Small Craft Advisory until 10 PM EDT Saturday for LHZ421-422.

Lake St Clair...Small Craft Advisory until 10 AM EDT Saturday for LCZ460.

Michigan waters of Lake Erie...Gale Warning until 4 AM EDT Saturday for LEZ444.

&&

$$

DISCUSSION...AA
MARINE.......AM
AVIATION.....AM


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