textproduct: Detroit/Pontiac

KEY MESSAGES

- Areas of fog possible this morning.

- Dry and pleasant conditions again today.

- Rain chances increase Wednesday and continue through Friday with cooler temperatures expected Friday into the weekend.

DTW THRESHOLD PROBABILITIES

* None

PREV DISCUSSION

Issued at 349 AM EDT Tue Sep 29 2026

DISCUSSION...

1018 mb surface high pressure drifts overhead this morning, causing calm winds to organize out of the southwest by early afternoon. For now, weak gradient flow and clear skies has led to early stages of radiative fog development. The best signal for this holds over the Saginaw Valley/Thumb in closer proximity to lake moisture, but not out of the question to see some patchy fog develop further south. Otherwise, expecting another sunny and dry fall day with highs in the mid-70s.

In regards to our late week system, there have been a few notable trends in the 18z/00z guidance. The first is Wednesday, in which models are trending toward a stronger southern stream low lifting along the eastern CONUS ridge and into northern Lower MI. The stronger wave is able to flatten the western flank of the ridge to bring forcing/moisture and thus rain chances into the Saginaw Valley/Thumb regions Wednesday morning. There are still concerns about how well the low levels can top-down saturate given the lag in Gulf moisture transport, but recent soundings show a shallower layer of dry air. NBM PoPs have increased accordingly with 40-60% rain chances showing up north of M-59 for Wednesday. Elsewhere, increasing cloud cover is expected but greater depth to the dry air should keep precipitation limited Wednesday.

Second trend has been a more uncertain forecast for Wednesday night into Thursday as Hurricane Polo makes its extratropical transition and sends a warm front into the Great Lakes. The trend has been for the bulk of moisture transport to be anchored more closely to the deformation axis, keeping it west of SE Michigan. Disjointed column moisture thus limits confidence in rain chances until the next wave of moisture arrives Thursday night. Regardless of moisture transport, the strong SW LLJ will ensure warmer temperatures Thursday with highs in the upper 70s and breezy conditions (20-25 mph gusts).

While model divergence increases daytime Thursday, it then converges again as the cold front slides through early Friday morning and connects with the shearing tropical moisture. This will be our best chance at heavy rainfall as models hint at frontogenetic enhancement to the precipitation axis, even as MUCAPE holds under 500 J/kg. One of the other notable trends in the guidance was the phasing of the Pacific closed low with the northern stream trough, which ultimately delays the clearance of the surface trough to Friday afternoon. This keeps rain chances going through at least the first half of Friday, which combined with earlier start to precipitation Wednesday boosts QPF totals toward an inch or greater by Friday night. This will especially be the case north of M-59, where there has been an increase in the number of 1+ inch ensemble member forecasts.

Aggressive drying trend arrives Friday night into Saturday post- front. Assuming saturated ground and full clearing, radiative fog potential returns Saturday morning. Encroaching thermal trough will bring high temperatures for next weekend into the mid-60s with lows in the 40s.

MARINE...

Light and variable winds mainly under 15 knots today as high pressure slowly slides east of the central Great Lakes. South to southwest winds will then increase ahead of the next cold front, which slowly moves through on Thursday. With the warm advection leading to more stable profiles and showers moving through during this timeframe, wind gusts are expected to top out only around 25 knots. A better chance to briefly exceed 25 knots exists behind the front Thursday evening/night with cold advection, as 850 MB temps lower into the mid single digits by Friday morning.

Another large area of high pressure building in on Friday and Saturday will promote light winds for the first half of the weekend. A stronger low tracking through the northern Great Lakes for the second half of the weekend brings another opportunity for winds to reach or exceed 25 knots over lake Huron.

DTX WATCHES/WARNINGS/ADVISORIES

MI...None. Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...None.