textproduct: Detroit/Pontiac

KEY MESSAGES

- Widespread rain and thunderstorms are expected this evening. Heavy rainfall is likely which may lead to localized flooding, especially in urban areas. A Flood Watch is in effect for areas south of M-46.

-There is also some potential for severe weather in the same area tonight. If severe weather occurs it would be isolated damaging wind gusts with isolated tornadoes possible.

- Breezy on Thursday with westerly wind gusts of up to 35 mph.

- Slightly below normal temperatures are expected through the week and this weekend.

DISCUSSION

Our strong June upper wave clearly located over the upper MS River valley will move across Lower MI tonight. The associated nose 130kt jet with the strong June surface low around 990 mbs also moves across Lower MI tonight. This brings large scale forcing and lift along and just north of the track of this surface low. 12z model suite is a little farther north with this forcing generally between M-59 and M-46. The complicating feature is the residual IL MCS and its affects on the surrounding area through the afternoon and into the evening and the impacts on the anticipated wx.

The 12z models had a decent handle on this morning's evolution of this system which forced the outflow boundary well south into central or even southern IL. A wake low has developed over Northern IL with several peak gusts around 50kts. The evolution of this feature will be watched to see if a short-fused wind headline might be needed late this afternoon, especially for the metro Detroit area. Anticipate that it is stable enough over SE MI that a wind headline won't be needed.

The combination of that outflow boundary being that far south with the warming mid levels from the MCV and evaporative cooling from the stratiform precipitation doesn't allow much if any instability to build anywhere in or around SE MI. The region will be left for the forcing from the upper wave to destabilize the mid layers of the atmosphere and see if we can have enough of a neutral low level profile to allow for some tornado potential or isolated wind to reach the surface. Between 00z and 06z there is some model agreement that potential still exists as MUCAPES get up to 500-100 J/kg with the 0-1km Richardson number getting down to around 0.25 for some potential connection to the surface. The severe weather outlooks are warranted by also are very conditional on those elements coming together this evening.

There continues to be the threat of heavy rain, but even that threat is more conditional. The best forcing on the nose of the low level jet brings in the high theta-e air from 925-850 mbs. This is also the favorable location where 3-6 hours of training of convection could occur and that is likely to be along and just north of the track of the surface low. 12z guidance has shifted that threat farther to the north. Have expanded the Flood Watch to account for that and will keep it in place for metro Detroit given the large urban footprint that doesn't require as much rainfall to create flooding issues.

In the wake of our overnight system, gusty winds will be the concern late tonight into the first half of Thursday especially for metro Detroit on south. There is good wind in the column with around 40 kts at 925 to 850 mbs with model soundings indicating steeper low level lapse rates allowing mixing. Local probabilities suggest wind gusts in excess of 30 mph but not likely to reach 45 mph advisory level. Otherwise a cool day with a chance of a morning shower and a slow decrease in clouds during the afternoon.

Surface high pressure moves into Lower Michigan on Friday for a quiet, seasonably cool mid June day. The next system moves in on Saturday but it is relatively weak with limited moisture so our chance POPs will only be around 30 percent. Another brief break until the next strong wave impacts the area late Sunday and Sunday. 12z GFS and ECMWF suggest just the southern few tiers of counties in Lower MI to get the stratiform rain and showers with this system. Then it dries out early next week with a slow warming trend with rising heights.

MARINE

A strong low pressure system is expected to trek across Southern Michigan tonight, with that bringing along the low threat for some thunderstorms capable of strong damaging wind gusts and potentially a waterspout or two as well. Western Lake Erie and Lake St. Clair have the potential to see isolated wind gusts of 40+ knots this evening into the overnight hours, both with and outside of thunderstorm potential, with wind direction taking a gradual shift from southernly flow this evening to more westerly flow tomorrow morning. Once the cold front passes through after midnight tonight the region could still experience 25 to 30 knot gusts through the early morning to afternoon hours tomorrow. In southern Lake Huron and the Saginaw Bay there is the potential for brief gust to gale winds late tonight, with gusts of 20 to 25 knots expected through tomorrow morning. Overall the threat remains across the whole region for scattered to numerous showers from now until the early morning hours, with the possibility of some embedded thunderstorms that could lead to an isolated chance of severe weather, the main hazard being wind gusts of 45+ knots and potentially a waterspout or two as well.

Winds gradually diminish tomorrow evening as the low-level winds diminish, however, there will be a continued chance for some rain showers through the afternoon. Northwest flow continues through Friday which will place the stronger winds across northern Lake Huron with gusts to 20 to 25 knots possible. High pressure briefly settles in Friday night to Saturday morning, relaxing wind speeds.

HYDROLOGY

A strong low pressure system will arrive this evening, producing widespread rainfall with numerous heavy thunderstorms through late tonight. Rainfall totals up to 1 inch are likely for much of SE MI, and isolated areas may receive 1 to 3 inches. Most of this rainfall is expected to occur in 4 hours or less, currently centered between 8pm and 2am. Rainfall rates will likely exceed 1"/hr at times. The most likely area to get the heavier rainfall has shifted farther north to areas around Pontiac, Flint and possibly as far north as Saginaw and Caro. This rainfall may pose a flash flooding threat, mainly in urban areas, and rises on rivers and streams can be expected. The Flood Watch has been expanded for areas along M-46 and I-69. The watch continues for areas south of M-59 mainly due to most of those locations being more urban with less rainfall still leading to flooding concerns.

PREV DISCUSSION

Issued at 150 PM EDT Wed Jun 17 2026

AVIATION...

Extensive midcloud and cirrus shield associated with IL MCS is now pushing into the forecast area this afternoon. Persistent high based stratiform light rain has been steadily pushing towards the area. Did move up the TEMPO timing for VFR light sprinkles this afternoon beginning after 18z. Will need to monitor the potential for increased surface winds due to wake low forcing after 20z, however, relatively deep static stability may limit the depth of fluxing downward momentum. Abrupt 850-700mb moisture advection on nose of old low level jet will result in rapid saturation throughout the column after 22z this evening. A dynamic upper level low pressure system will lead to a very favorable setup for strong vertical ascent over Southeast Michigan between 23-05z. Difficult forecast ahead assessing exactly where the preferred location will be of the frontogenesis. Did introduce a TEMPO for +TSRA at MBS and FNT this issuance and further refinement of the heavy rainfall in the TAFS will be needed as trends emerge. The potential exists for drizzle to persist into Thursday morning. Strong gradient west winds of 15 to 30 knots are expected by mid to lake morning hours Thursday.

D21/DTW Convection...Much more uncertainty exists where the heaviest band of thunderstorms and heavy rain will develop. Latest model data supports areas north of DTW. Severe weather still remains possible although the greatest threat remains to the southwest of the airspace.

DTW THRESHOLD PROBABILITIES...

* Low for ceilings aob 5kft today. High tonight.

* Moderate for thunderstorms this evening.

DTX WATCHES/WARNINGS/ADVISORIES

MI...Flood Watch through late tonight for MIZ053>055-060>063-068>070-075- 076-082-083.

Lake Huron...Small Craft Advisory from 8 PM this evening to 8 PM EDT Thursday for LHZ421-422-441>443.

Lake St Clair...Small Craft Advisory from 8 PM this evening to 8 PM EDT Thursday for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory from 8 PM this evening to 8 PM EDT Thursday for LEZ444.