textproduct: Detroit/Pontiac

KEY MESSAGES

- Thunderstorms increase coverage and intensity while spreading from the Tri Cities and northern Thumb toward metro Detroit today.

- Isolated damaging wind gusts and locally heavy rainfall are the primary hazards with the strongest storms this afternoon and evening. The best chance for marginally severe storms is across the Detroit Metro Area and points south.

- Dry weather and near-normal temperatures settle in for the weekend.

- A new heat wave is on schedule for next week (3 consecutive days of highs 90+ degrees).

DTW THRESHOLD PROBABILITIES

* Medium for thunder this afternoon and/or evening.

* Medium for ceilings at or below 5,000 feet this afternoon and evening.

PREV DISCUSSION

Issued at 350 AM EDT Thu Jul 9 2026

DISCUSSION...

Showers and a rumble of thunder, ongoing over central Lower Mi at forecast issuance, is sustained by a well-defined MCV shown in composite radar data. It is embedded within the low to mid level moisture axis positioned SW to NE ahead of the surface front. There is also some lingering elevated instability judging by the 00Z DTX and model soundings, an environment capable of sustaining the showers and producing a rumble of thunder through early morning.

The forecast is also focused on initiation timing of the new surface based convective cycle as the front settles slowly southward across southern Lower Mi this afternoon and evening. A preferred scenario has an early day round of storms ahead of the front followed by or merging with a late day and evening phase of activity accompanying the frontal passage. The early day phase is tied to differential heating created by the showers leading up to sunrise and a hefty band of cloud debris that lingers during the morning. An outflow boundary in surface analyses has potential to provide a focusing mechanism in the differential heating zone generally north of I-69 as surface instability quickly increases. Model soundings are uncapped and favorable for development around or shortly after 12 PM as HREF mean surface based CAPE increases into the 1000-1500 J/kg range. Thunderstorm clusters move from there southward toward metro Detroit mid to late afternoon while approaching severe intensity on an isolated basis and in line with the SPC Marginal Risk. Multicell organization is reachable in 25-30 kts of westerly 0-6 km bulk shear, although shown in model data to decrease from north to south across the region. Locally heavy rainfall also remains a hazard to highlight as PW rises into the 1.5 to 2 inch range within the moisture axis ahead of the front. The front itself then becomes the focus for a second round of storms that develop back toward the Tri Cities and northern Thumb late in the day and this evening. Intensity will be strongly dependent on recovery of instability before daytime heating wanes after 00Z, however scattered to numerous coverage is expected to fill in along the front as it moves into and south of the I-69 corridor this evening.

The surface front/wind shift is then on schedule to move south of the Ohio border early Friday morning. The new 00Z model runs remain in good agreement on this timing, along with a few showers within the trailing mid level frontal zone still over SE Mi through the morning. Chance/scattered coverage looks reasonable in the 00Z NBM forecast update for the area generally south of I-69 Friday morning. The long wave ridge building over central Canada and the northern Plains produces surface high pressure in northern Ontario and Quebec that is strong enough to push the front farther into the Ohio valley Friday afternoon and night. The inbound air mass is slightly cooler and less humid as shown by consensus model projections of surface Td dropping into the 50s Friday night and Saturday.

Continued amplification of the mid/upper level long wave ridge is centered over the Plains with a tilt toward Hudson Bay by Sunday. This configuration favors leaning the forecast toward a few days of dry weather while monitoring convective trends to the north. This leads into the weather highlight for early next week tied to a new round of heat on track to increase as the mid/upper level ridge builds into a west to east configuration from the Plains into the Great Lakes. This is in a better position to block Gulf/Atlantic humidity as a limiting factor for heat index, however the strength of the ridge adds confidence to a return of lower to mid 90s in guidance temperatures for the early to middle part of next week.

MARINE...

This afternoon we expect to have a weak low pressure system trek across North Lower Michigan, bringing the chance for showers and even an isolated severe weather threat from Saginaw Bay down to the Lake Erie shore. The main threat for any thunderstorms that could develop would be wind gusts of 34+ knots. Nonetheless Lake Huron and Saginaw bay can expect light winds veering from the southwest to the north throughout the day, with gusts of 15 to 20 knots possible depending on the positioning of the low pressure. Lake St. Clair and Lake Erie shore can expect light winds as well veering from the southwest to the west throughout the day.

Tomorrow looks to potentially bring some modest wind flow to the Lake Huron and Bay area as a modest pressure gradient could develop between a departing low pressure and developing high pressure. This could lead to some enhanced wind flow in the bay depending on the positioning of these systems. Flow is expected to be out of the Northeast at 10 to 15 knots, with gusts of 20+ knots possible in the afternoon/evening hours. Lake St. Clair and Lake Erie Shore look to be more tame with light winds out of the north expected.

A high pressure system is expected to develop over the region throughout the weekend, bringing warmer and calmer weather.

HYDROLOGY...

A slow moving cold front is on schedule to settle through southern Lower Michigan today and tonight serving as the focus for numerous showers and thunderstorms. The greatest coverage and intensity is expected this afternoon and evening with a chance of locally heavy rain across the area. Basin average rainfall of a quarter to a half inch is most likely with a chance of near 1 inch in scenarios with greater thunderstorm coverage. The slow movement of the front could also produce more than one round of thunderstorms leading to localized totals greater than 1 inch within a few hours time. This presents minor urban flooding potential along with ponding of water on roads and in other prone areas. Scattered showers and a chance of thunderstorms lingers into Friday, mainly south of M-59, before coming to an end Friday afternoon.

DTX WATCHES/WARNINGS/ADVISORIES

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