textproduct: Detroit/Pontiac

KEY MESSAGES

- An Extreme Heat Warning remains in effect. It will remain hot and humid on thru Friday, with high temperatures in the low to mid 90s. - A marginal risk of isolated severe thunderstorms exists this afternoon through tonight, and continues Friday and Saturday. - Increasing coverage of showers and thunderstorms on Friday, continuing at times over the weekend. will bring an isolated flood threat.

- A gradual cool down begins on Saturday, with highs finally dropping into the 80s by Sunday.

UPDATE

While there remains uncertainty in timing of convection on Friday, probabilistic guidance is leaning toward higher chances for thunderstorm initiation later in the day, with highs able to achieve low to possibly mid 90s. Considering the cumulative effects of heat, the excessive heat warning was extended to 8 PM Friday. The exception was across the Tri Cities and thumb where potential earlier convection timing and cloud cover result in a wide range of potential highs among the ensemble guidance (mid/upper 80s to low 90s). This may warrant in the issuance of a heat advisory for these northern counties at 8 PM once the heat warning expires rather than an extension of the current warning.

Decaying convection which tracked across central Lake Mi earlier has driven an outflow boundary into SW Lower Mi. This outflow is likely to erode prior to making much inroads into Se Mi, with the possible exception of the Tri Cities. While the outflow has resulted in a localized reduction in sfc dewpoints to the west, the expectation is for a more backing of the low level flow to the WSW this afternoon to either sustain or advect lower to mid 70 sfc dewpoints into Se Mi. So no changes to the current forecast temps and heat indices appear warranted this morning.

The 12Z DTX sounding showed a very strong capping inversion. This suggests nothing more than a potential for isolated late day convection given limited erosion of the cap expected today.

PREV DISCUSSION

Issued at 616 AM EDT Thu Jul 2 2026

AVIATION...

A very moist and unstable background environment will provide the underlying support to maintain at least a low probability for thunderstorm development thru the taf period. Upstream radar trends show a lingering area of convection lifting across central lower mi. There remains some potential for this activity to hold together and push toward mainly MBS yet late this morning. Otherwise, prospective development possible at any location this afternoon into tonight. A very low confidence setup in terms of offering greater detail on timing or scale/location. At this stage, will continue to refrain from offering a defined mention at any one location and allow trends to develop and update as necessary. A brief MVFR to low VFR diurnal cu likely to emerge as daytime heating takes hold, with cloud base gradually lifting toward a higher based VFR deck with time.

D21/DTW Convection...There is an isolated thunderstorm potential for the D21 airspace on Thursday afternoon/night.

DTW THRESHOLD PROBABILITIES...

* Very low for thunderstorm potential this afternoon through tonight.

PREV DISCUSSION... Issued at 245 AM EDT Thu Jul 2 2026

DISCUSSION...

An Extreme Heat Warning remains in effect through this evening, though the northern half of the CWA may struggle to reach a 105 heat index due to slightly lower temps and dew points. Max temps yesterday ended up in the mid to upper 90s, right on target, as the 00z DTX sounding indicated an 850 MB temp of 22 C. Fortunately, some drier low level air worked in from the south, dropping surface dew pts into the upper 60s to lower 70s late in the day. This pocket of drier air extending to 850 MB level will be exiting east this morning as pseudo tropical moisture returns today. With the return of higher surface dew pts (low-mid 70s) and moistening at 850 MB, 850 MB temps only progged to peak out around 21 C. Thus, we are looking at mostly mid 90s for high temperatures today (supported by NAM/ECM mos guidance). This holds especially true if convection develops this afternoon, which remains a valid concern given the level moisture advection and remnant outflow boundary from early morning storms over northern Lower Michigan.

Forecast soundings show CIN getting eroded during the day or dropping to minimal values. the preference is to carry at least slight chance pop for thunderstorms this afternoon and especially this evening. This is particularly true over the southern half of the CWA, where steep mid level lapse rates persist, K indices push into the 35-40 C along the southern Michigan border, and upper level PV advection works through western Ohio. With MLcape in excess of 2000 J/kg and 0-6 KM bulk shear in the 25-30 knot range, severe storms are a distinct concern; the 00z RRFS indicates isolated discrete storms late in the day.

The Midwest storm breeding ground will remain active as multiple shortwaves track out of the Central Plains this evening through Friday. As low level winds veer around from southwest to west this evening/tonight, there is some concern for possible training of storms along/close to the southern Michigan border. However, plenty of discrepancies remain regarding how fast upstream activity will advance downstream and survive into southern Lower Michigan.

A high degree of uncertainty persists regarding temperatures and timing of showers/thunderstorms on Friday,though the NBM pops still favors likely pops late in the day and evening. This delayed timing would also allow heat indices to flirt with 105 degrees once again, and will defer to the day shift to finalize heat headlines. Later timing would be more favorable for severe storms as well, but SPC 2 outlook is marginal for now.

The pattern for the weekend looks wet as significant upper level energy emerges from the Rockies and a seasonably strong upper level trough develops over the Upper Mississippi River Valley by Saturday. The main question is will it advance east into the Central Great Lakes as two distinct pieces or as one main during the second half of the weekend. Canadian ensemble members favor a faster Saturday progression, showing 30-40% probability of a 24 hr QPF total >1" over the Detroit Metro area, while the Euro ensembles favor Sunday. Either way, localized flooding will be a concern on either day.

MARINE...

High pressure remains nearly stationary over the southern Appalachians through the late week, maintaining a feed of a hot and humid air into the Great Lakes. Prevailing wind remains from the south and southwest at 10 to 15 kt with gusts generally capped around or below 20 kt due to higher stability over the relatively cooler water. Lake Huron will reside near the edge of the cap which offers potential for multiple rounds of thunderstorms today. Isolated severe thunderstorms will be possible, capable of producing wind gusts in excess of 50 kt and large hail. The cap migrates farther south by Friday which brings higher chances for storms to the rest of the region. A cold front then sags south on Saturday, bringing a wind shift to the north and maintaining the potential for scattered showers and storms.

CLIMATE...

Daily Records for rest of the week...

Detroit Record High Record Warm Minimum Thu July 2 99 (2011) 76 (2018) Fri July 3 100 (1911) 78 (1911) Sat July 4 102 (2012) 79 (1921)

Flint Record High Record Warm Minimum Thu July 2 100 (1931) 73 (2002) Fri July 3 99 (1921) 73 (1983) Sat July 4 102 (1921) 76 (1999)

Saginaw Record High Record Warm Minimum Thu July 2 100 (1931) 73 (2002) Fri July 3 99 (1966) 76 (1974) Sat July 4 97 (2012) 75 (2012)

DTX WATCHES/WARNINGS/ADVISORIES

MI...Extreme Heat Warning until 8 PM EDT this evening for MIZ047>049- 053>055.

Extreme Heat Warning until 8 PM EDT Friday for MIZ060>063-068>070- 075-076-082-083.

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