textproduct: Detroit/Pontiac

KEY MESSAGES

- Hot and humid conditions through tomorrow.

- A Marginal Risk for severe weather is in place through tonight, with a Slight Risk for tomorrow and tomorrow night.

- More shower and thunderstorm chances Thursday and Friday.

DISCUSSION

A challenging forecast continues to plague the Great Lakes Region. A hot and humid air mass with a high degree of instability is in place this afternoon. Temperatures have reached into the upper 80s to 90 degrees as of 2 PM, with heat indices well into the 90s. A couple more hours left to increase those values as well. The broken line of convection which was just south of the border this morning within the northern edge of the 850-700 MB Theta-E ridge has crept northward into southwest lower Michigan and will continue to drift north, presenting a opportunity for showers and thunderstorms this evening and tonight. The highest instability and wind shear are actually located over center/northern Lower Michigan this afternoon per SPC mesoscale analysis, making areas north of M-46 probably the greatest concern for isolated severe storm, but the entire CWA has a Marginal Risk through tonight. Once again, hi-res solutions continue to underestimate the coverage of showers and thunderstorms.

A couple opportunities exist for ridge runners as upper level impulses eject out of the central/northern Plains both Wednesday and Thursday. Growing consensus points to a shortwave tracking through northern lower Michigan tomorrow (15-19z), with a surface front/reflection along or north of I-69 providing the focus. Even with this potential earlier timing, there will most likely be sufficient instability around to support severe storms alongside high 0-6 KM bulk shear values aoa 50 knots. A Slight Risk of severe weather remains in place for both large hail and damaging winds. Machine learning even highlights the northern Thumb region for a tornado threat, which is supported by 0-1 KM bulk shear values around 25 knots. If this faster timing materializes, max temperatures could come up short of the outgoing forecast in the 90- 94 degree range; thus, confidence is not high enough to issue a Heat Advisory, as peak values in the upper 90s to around 100 degrees could be short-lived once again.

Yet another upper level impulse will race through Wednesday night or Thursday morning. Coupled with nocturnal low level jet enhancement, strong thunderstorms producing heavy rain become a concern. Although, at this time, there is no indication of training. None-the- less, PW Values aoa 1.75 inches and 700 MB dew pts still locally nearing 5 C will certainly be supportive of locally heavy rain, with another opportunity or two between Thursday night and Friday night. Confidence remains low, however. Longwave pattern guidance for the weekend indicates upper level confluent flow and subsequent high pressure building in, trending the forecast in a drier direction.

MARINE

A low pressure system now entering Ontario will steer the weather across the Great Lakes through mid week. The warm front is now east of Lake Huron with the cold front approaching Lake MI leaving us in the hot and humid warm sector. Though the airmass is mostly stable at this time, it hasn't taken much mid level energy to spark clusters of storms the last few days. The cold front will slowly enter lower MI and drift SE today and tomorrow leading to additional rounds of storms through Wednesday night and even into Thursday if the front stalls over the area. The weak gradient will keep speeds down through the week though with max wind gusts rarely touching 20 knots. The slightly cooler air over the waters brings chances of waterspouts with any of the storms over the lakes this week. The very humid airmass over the lakes will also lead to fog development over the waters, mainly the north half of Lake Huron which will need to be watched for another possible Dense Fog Advisory tonight.

HYDROLOGY

A humid air mass will bring a chance of heavy rainfall within any strong thunderstorm that develops. However, areal coverage and exact timing remain elusive across Lower Michigan. Periodic chances of storms will exist right through Friday. Any strong thunderstorm will have the potential to produce a quick 1-2 inches of rain, which can lead to localized minor flooding of roads and poor-drainage areas. There are currently no indications of training storms, though more extensive flooding would become a concern if a mature MCS develops.

PREV DISCUSSION

Issued at 142 PM EDT Tue Sep 1 2026

AVIATION...

Deep capping layer around 4.0 kft agl and strong convective inhibition is expected to limit thunderstorm activity across the majority of Southeast Michigan this afternoon and evening. Elevated altocumulus/accas pushing off of Lake Michigan is associated with a surge of 850-700mb thetae advection that will push towards the Detroit terminals between 18-21z. Uncertainty exists whether or not any of this elevated shower activity will breach the cap and become surface based. If it were, then TSRA would be possible late this afternoon at DTW. Will monitor trends. Model signal then suggests thunderstorms will be possible late this evening across the Central Lake Michigan basin. There is data that suggests TSRA will be possible at MBS and FNT tonight between 05-08z. Included as a Prob30 group. Otherwise, very low confidence in convection occurrence and timing exists in this pattern.

D21/DTW Convection...Will watch shower activity push towards and to the south of DTW. Decided to go with VCSH as current trajectory suggests south and west of the terminal.

DTW THRESHOLD PROBABILITIES...

* Low this afternoon and evening.

DTX WATCHES/WARNINGS/ADVISORIES

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