Area Forecast Discussion

KEY MESSAGES

- Heat indices peak in the 90s this afternoon and evening.

- Severe thunderstorms possible tonight, mainly between 9 PM and 1 AM; damaging winds, large hail, and/or spin-up tornadoes possible.

- Not as warm and much less humid Friday through the weekend with additional showers and some thunderstorms possible Saturday night into Sunday morning.

DISCUSSION

An anomalously muggy airmass persists today with heat indices attempting to lift back into the 90s for parts of Metro Detroit south. Expired the heat advisory early as temperatures and dewpoints have risen slower than forecast. Heat indices are now only expected to peak in 90s through the rest of today. CAPE values are on the rise amidst low afternoon cloud fraction. This uptick in instability prepares the atmosphere for nocturnal convection. An evening squall line is emerging upstream, attendant to a dynamic cold front, which tracks eastward into the area after dark. 11.18Z KDTX RAOB shows a lot of dry air still around with CIN persisting around 580 mb and 825 mb preventing free convection.

CAMs offer slight differences in timing of the main convective line, once it moves into Southeast Michigan. 9 PM appears to be the earliest arrival time for western Midland or Lenawee Counties, before the line continues eastward across the rest of the region. SPC's SWODY1 continues to advertise Slight to Enhanced Risk for the forecast area, while model trends indicate increasing potential for a weaker progression as it moves through. The nocturnal timing doesn't help with a surface-based CAPE reduction, while the reservoir of higher instability still lies well-off to the west, over southwest Lower and northern Indiana. That is where the greatest instability gradient lies with potential for discrete cells before they eventually merge with the main line. A bow-echo should emerge with enhanced RIJ dynamics and very strong shear as the line reaches the local area presenting highest confidence in a severe wind threat. The greatest adjustment this forecast cycle is focused along the northern extent of the anticipated linear convection. Confidence is falling in sufficient instability for widespread severe hazards north of I-69, therefore the area of greatest concern lies between the Ohio border and M-59, especially for areas west of US-23. 30 knots of EBS and 100 m2/s2 of 0-1 km SRH favors rotating updrafts, and some hodographs indicate higher potential for QLCS tornadogenesis. Lower confidence in severe-level winds with increasing eastward extent across the CWA.

Governing/digging mid-level shortwave clears overhead by 09Z Friday, ushering the cold front out. Gradient/column flow veers zonally as 500 mb heights rebound with increasing stabilization. Surface high pressure builds southeastward, out of The Plains, and into the lower Ohio Valley. Forecast soundings indicate aggressive column drying during the morning hours with PWATs dropping from 1.75 inches to 0.50 inches between 00Z and 12Z Friday. No precipitation concerns the rest of the day with limited diurnal cumulus response. Lower column dynamics still support renewed breeziness with a dry 5 kft boundary layer, mixing down 20-25 knot flow.

The weekend forecast features a mix of warm and dry weather Saturday followed by another cold front with precipitation Saturday night into Sunday morning. 850 mb temperatures climb into the teens (Celsius) Saturday, with highs in the mid-upper 80s and ample sunshine. Another wave then moves in late Saturday into Sunday with potential for some showers and thunderstorms. Much cooler air fills in behind the front marking a more tranquil period of weather from Sunday into early next week. Thermal troughing keeps highs below normal, in the low-mid 70s through at least Wednesday. The next chance for rainfall comes sometime Tuesday.

MARINE

The next line of storms is expected to pass through the southern Great Lakes later this evening into tonight around 11pm to 3am just ahead of a cold front. The front will be tied to a low pressure system lifting from southern WI into eastern Ontario. Winds will increase from the southwest, turning more westerly, behind the front offering a period of gusts to near 30 knots for Saginaw Bay and the tip of the Thumb tonight into Friday morning so a Small Craft Advisory is in effect. In the vicinity of the storms tonight, wind gusts in excess of 50 kt and large hail would be the main threats with these storms. This front will pass through early Friday morning, but a second cold front will set up just west of the Great Lakes to start the weekend which will keep elevated southwesterly winds across the lakes through much of Saturday before the front then sweeps east by Sunday morning. Winds will stay elevated around 20 knots, but out of the northwest Sunday.

PREV DISCUSSION

Issued at 126 PM EDT Thu Jun 11 2026

AVIATION...

Strong anticyclonic vorticity advection signal with relatively deep static stability between 4.0 and 16.0 kft agl will suppress upward vertical motion throughout much of the afternoon and into the early evening. In fact many areas south of I 69 are void of cloud at the moment. Shallow boundary layer cloud exists across the Tri Cities and Thumb. Height falls ahead of vorticity maximum will lead to rapid moisture transport/recover right ahead of approaching cold front. Best time for thunderstorm activity now appears to be between 03-05z. Little opportunity exists for showers and/or thunderstorms before then. The main cold front and dewpoint gradient is expected across Southeast Michigan between 08-11z Friday morning. Strong stability between 2.0 and 10 kft agl and a very dry airmass will limit cloud development Friday.

D21/DTW Convection... A line of thundestorms is expected to push across DTW between 4-6z. It remains possible that strongest thunderstorm activity could push south and west of the terminals.

DTW THRESHOLD PROBABILITIES...

* Moderate for ceiling aob 5000 feet this afternoon, high tonight.

* Moderate for thunderstorms between

DTX WATCHES / WARNINGS / ADVISORIES

MI...None. Lake Huron...Small Craft Advisory from 10 PM this evening to 10 AM EDT Friday for LHZ421-422-441.

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