textproduct: Detroit/Pontiac

KEY MESSAGES

- One or possibly two rounds of showers and thundestorms are expected to track through southeast Michigan this evening and tonight. Isolated storms will be capable of producing damaging wind gusts, large hail, and flooding rainfall. Locations near the southern Michigan border carry the highest risk.

- Seasonable temperatures continue into mid week, with chances for thunderstorms primarily focused near the southern Michigan border Monday night and Tuesday.

- Dry weather is expected to end work week.

DISCUSSION

A stable airmass in place over southeast Michigan for now, as dew pts started the day in the 50s. A MCS over the western Great Lakes tracking across southern Lake Michigan will attempt to transport moisture/instability across the border by early this evening. Surface dew pts are currently lowers 70s degrees over northern Indiana. Sufficiently strong (40 knots) southwest low level jet early this evening to transport instability/solid negative showalter indices into the south half of the CWA. The stronger wind fields and localized stronger 0-6 KM bulk shear will support a chance of severe storms, especially toward the southern Michigan border this evening where the sharp instability gradient will reside. Machine learning suggests all severe hazards are in play, including an isolated tornado as 0-1 KM bulk shear increases above 20 knots. Despite mid level lapse rates looking average, MLcapes aoa 1500 J/kg suggests large hail threat, which is in addition to the main hazard, damaging winds. However, if abrupt southeast development occurs with the upstream MCS and it dives into northern Indiana (a distinct possibility), our severe threat will be diminished as the moisture transport fails to materialize. Regardless, the deep moisture plume (PW up to 2 inches) looks to be fold over and descend south into the Ohio Valley overnight as 850 MB winds veer more westerly. Thus, chances for training and significant flooding rainfall seems to be low locally, with much higher chances over the northern Ohio Valley.

There is fairly good model agreement regarding subsidence and dry conditions for most of Monday, before some late-day attempt to destabilize as a subtle shortwave rides along in the west-northwest upper level flow established over the Great Lakes region. Once again, the corridor along and south of I-94 will have to be watched for possible severe storms during Monday evening/night.

The close proximity of the moisture axis and substantial instability over the Ohio Valley on Tuesday will also need to be watched closely as the strength of upstream shortwave tracking through Midwest is assessed. NBM pops suggest sufficient moisture transport returning into the southern part of the state will supports likely showers and thunderstorms near the border, along with a low severe threat.

The jet stream/strong westerlies will remain across the northern Great Lakes through bulk of the work week and will become enhanced on Thursday as upper-level ridge builds over the southeastern United States to close out the work week. Predominately confluent upper level flow supports dry conditions and near-normal temperatures.

MARINE

A slow moving, stalled frontal boundary will impact the region through middle parts of the week, leaving varying wind directions at times and winds generally less than 20 knots. Multiple rounds of thunderstorms are possible through mid-week, especially across Lake Erie where chances are greater for severe weather and strong thunderstorm winds. By mid to late week, a weakly organized area of low pressure becomes develops across the Northeast, followed by high pressure of 30.1 inches gradually dropping southeast across the central and eastern Great Lakes. This will favor an uptick in northwest winds Wednesday through Friday.

HYDROLOGY

One or possibly two round of showers and thundestorms are expected to track through southeast Michigan this evening and tonight. Given the progressive nature of this activity, and with the most intense convection likely remaining south of the border, the chances for significant flash flooding remains low (barring unforeseen training of storms). Nonetheless, a few strong thunderstorms will bring rainfall rates in excess of an inch per hour, which could still cause minor flooding in urban and poor-drainage areas. The daytime hours of Monday look to be mainly dry before another low chance of heavy rain producing storms develops near the southern Michigan border.

PREV DISCUSSION

Issued at 206 PM EDT Sun Aug 9 2026

AVIATION...

Storm system approaching from the west will move into an environment with less instability. Uncertainty exists in regards to the maintenance of this system into the southeast Michigan corridor and if enough instability can be drawn up into the area as system moves east. Current timing if it holds together could put it an hour or two earlier, but models that have the best handle on this system puts the better thunderstorm activity in around 22-23Z and after while placing stronger storms south of terminals. Have adjusted timing slightly based on this and will amened as needed with southern terminals holding best chance to see any stronger thunderstorm activity. VFR conditions with overcast high clouds preceding activity this afternoon under a S-SW wind up to 10 knots with a chance for continued support of showers and thunderstorms into the early part of tonight. MVFR to borderline MVFR ceilings will follow late tonight/tomorrow morning as winds become more westerly.

D21/DTW Convection... No thunderstorms through bulk of this afternoon. Upstream storms over Lake Michigan have developed, but uncertainty in maintenance in strongest storms into the metro area remains relatively high. Best chance remains towards 23z and into early tonight for any thunderstorm activity.

DTW THRESHOLD PROBABILITIES...

* Low for thunderstorms late this afternoon into tonight.

DTX WATCHES/WARNINGS/ADVISORIES

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