textproduct: Detroit/Pontiac

KEY MESSAGES

- Isolated thunderstorms are possible through this afternoon and evening with a low probability for severe weather and localized heavy rainfall.

- The potential exists for showers and thunderstorms to develop both Wednesday and Thursday.

- Drier conditions develop Friday through most of Saturday.

- Renewed chance of storms and potential for heavy rainfall by Saturday night into Sunday.

DISCUSSION

Fast west-northwest upper flow remains directed across the Great Lakes tonight through Thursday as the synoptic pattern holds relatively stagnant over much of the continent. This maintains a modestly unstable environment with periodic chances for shower and thunderstorm activity each day, but details on timing and placement will continue to be governed by smaller scale perturbations within the upper flow. Thus, this part of the forecast continues to carry relatively low confidence for the local area. The greater threat of severe weather and heavy rainfall will continue to be favored over the Ohio Valley through midweek.

For the near term, a mature MCV is driving decaying convection across northern OH along a CAPE gradient reinforced by remnant outflow from a morning MCS. The orientation of this gradient and Corfidi vectors favor further ESE propagation to continue along this corridor to our south. The northern edge of remnant convection is curling across areas south of I-94 with an isolated threat of a gusty winds to 40 mph and localized heavier rainfall, but this threat is rapidly sinking south of the border. Otherwise, stratiform rain passes across areas south of I-96 over the next few hours with upstream observations indicating potential for a few embedded lightning strikes.

After the MCS departs, outflow on the northern flank meets a diffuse stationary front positioned across southern lower MI and may provide the trigger for additional isolated to widely scattered smaller scale and disorganized convection south of I-69 the rest of the afternoon. The thick cirrus shield associated with the MCS has dampened afternoon destabilization, but latest mesoanalysis advertises 500 to 1000 J/kg of MLCAPE given sfc dew points in the lower 70s and mid-level lapse rates of 6.5 to 7 C/km. The main window for convection will be through about 8pm with any lingering activity tapering off by 10pm. Included a patchy fog mention tonight as the front lingers in the area with higher humidity and clearing skies.

Subtle height falls on Wednesday cause a weak surface trough/convergence axis to sink south from northern Lower into the Saginaw Valley and Thumb vicinity during the afternoon. This may be enough to trigger convection, and with the active jet overhead there will be a threat for isolated strong to severe wind or hail as well as a localized downpour. Hi-res ML guidance favors a window between 3pm and 9pm for any stronger convection. The favored area for convection on Thursday looks to again set up south of the area toward the Ohio Valley.

By late Thursday into Friday, the large scale pattern will begin to evolve with the western CONUS ridge amplifying over the Rockies. Surface high pressure builds across northern Ontario on Friday then migrates south into the Great Lakes to provide more tranquil and slightly cooler weather through most of Saturday. This is followed by a more potent system set to track across the Great Lakes on Sunday. Its warm front arrives late Saturday, bringing a chance of showers and storms by late evening. Ensemble QPF output indicates a threat for heavy rainfall somewhere in the vicinity - 13Z NBM advertises 30% for over 1 inch for parts of Lower MI by 00z Mon.

MARINE

Weak wind fields will remain in place through Thursday as a frontal boundary hangs around the Great Lakes region before dropping south Thursday night. Periodic chances of showers and thunderstorms will persist through that timeframe. Any strong thunderstorms will have the potential to produce hail and winds in excess of 35 knots. With the lighter winds, there are some weak signals for patchy dense fog over Lake Huron at times, through confidence remains low.

A large area of high pressure builds into northern Ontario Thursday night, allowing north-northeast winds to increase on Friday. Winds are expected to reach at least 20 knots over southern Lake Huron, which may allow waves to approach 4 feet over the southern basin. The ridge extending from the high slides through Friday evening, supporting lighter winds into Saturday morning. Southerly winds will then peak out around 20 knots ahead of a cold front Saturday night, with winds shifting to west on Sunday behind the front.

HYDROLOGY

Slow-moving thunderstorms embedded within a broader area of light rain will continue across areas south of I-94 through 5pm, bringing a threat for localized heavy rainfall in excess of 1 inch. Additional isolated thunderstorms are possible to develop this afternoon and evening, mainly south of I-69. These storms would also be slow-moving and pose a threat of localized heavy rainfall and isolated totals up to around 1 inch. Minor flooding in urban and poor drainage areas is possible through this evening.

PREV DISCUSSION

Issued at 138 PM EDT Tue Aug 11 2026

AVIATION...

A line of thunderstorms is ongoing across northern Indiana, with the bulk of the severe activity expected to remain south of the terminals this afternoon and evening. The northern portions of the line, however, may redevelop with frequent cloud to ground lightning strikes and an isolated strong to severe damaging wind threat. This activity is most likely to impact DTW/DET/YIP, but may reach as far north as FNT. Time of arrival is between roughly 19z and 00z. Outside of thunder chances, upstream cloud heights have fallen to between 1.0 and 3.0 kft agl, which will work east with the thunderstorm complex. Light east-southeast flow has held on longer than projected, and will likely hold until the MCV comes through before switching to the southwest. Clearing skies atop wet ground and calm winds tonight may lead to radiative fog development Wednesday morning.

D21/DTW Convection... the northern edge of a thunderstorm complex clips southern portions of the D21 airspace. The main concern is frequent cloud to ground lightning, but there is an isolated damaging wind threat as well. Timing is most likely between 20z and 23z.

DTW THRESHOLD PROBABILITIES...

* Moderate for thunderstorms this afternoon/evening.

* Moderate for ceilings 5000 feet or less through 00z.

DTX WATCHES/WARNINGS/ADVISORIES

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