textproduct: Detroit/Pontiac

KEY MESSAGES

- An Extreme Heat Warning is in effect Tuesday afternoon through Thursday for high temperatures reaching the mid 90s to 100 degrees and heat indices in excess of 105 degrees each day.

- There will be little nighttime relief as lows only cool into the mid 70s with heat index around 80 each night.

- Wednesday and Thursday are the hottest days, however hot and humid conditions also extend into Friday and the holiday weekend along with increasing potential for showers and thunderstorms.

DTW THRESHOLD PROBABILITIES

* None

PREV DISCUSSION

Issued at 353 PM EDT Mon Jun 29 2026

DISCUSSION...

Observations and the latest forecast data incoming today present no big changes to the trajectory of heat building across SE Mi through the mid week period. Today is the transition day as temperatures and humidity make a notable jump from weekend conditions while also buffered somewhat by the SE surface wind component and high clouds from convection across the northern Great Lakes. Highs in the lower 90s with heat index rising into the mid to upper 90s remain in reach this afternoon for interior locations while the clouds and SE wind maintain a cooler profile toward the shorelines.

Heat building into the extreme range during Tuesday is primarily driven by surface and low level wind veering SW in combination with the slightly eastward shifting 594 dm 500 mb ridge. These larger scale trends, also combined with deepening low pressure in central Canada, draw the full Bermuda high air mass into southern Lower Mi during the morning. Afternoon peak heating takes it from there for highs in the mid to upper 90s combined with surface Td in the mid to upper 70s yielding max heat index in the 105 to 110 range. Guidance temperatures in today's forecast package then identify Wednesday and Thursday as the peak in this heat event, at least in terms of max temperature. Both Wednesday and Thursday highs have a chance to reach 100 and have a chance to break relatively low hanging DTW record highs (ref Climate section below). Surface Td is projected to drop off a few degrees but still maintain heat index in the 105 to 110 range followed by nighttime readings only dropping into the mid and upper 70s with heat index around 80. Today's upstream observational evidence of these conditions across IL/IN and points south/west, combined with the expected magnitude and duration of this event, support the case for extreme heat and the upgrade from Watch to Warning issued earlier this afternoon for the entire period through Thursday.

Convective trends also demand forecast attention for both potential coverage of cloud debris and eventually downstream MCS trajectories. Low level jet supported activity last night into the still ongoing storms this afternoon are closely following the customary leading edge cap temperature of 10 C or warmer at 700 mb. This thermal ridge builds even more strongly over Lower Mi tonight into a position to support both peak surface temperatures and also direct new convection to the north closer to the surface front through Tuesday/Tuesday night. Cap predictability does drop off Wednesday as 700 mb temps moderate and the surface cold front reaches the Straits region, however the larger scale pattern still favors storms holding on a track across the northern Great Lakes through Thursday.

The ridge is further suppressed by the deamplifying northern stream mid/upper level westerlies during Friday. This is the first sign of heat dropping below peak, although the cold front is projected to stall and wash out across the northern Great Lakes for no real surface air mass change in SE Mi. The hazard potential of heat and humidity for this time period will be evaluated/updated in upcoming forecast cycles, however data appears to support at least some relief below the warning threshold during the holiday weekend.

MARINE...

A warm front lifts across lower MI this evening and tonight. Prevailing southeast wind on the order of 10 kt continues over the central Great Lakes with gusts to around 20 kt over Lake Huron. The front continues pushing northeast across Lake Huron on Tuesday with wind gradually veering to southwest as much warmer and more humid air builds into the area. The gradient will maintain SW wind of 10 to 15 kt Tuesday through Thursday, with gusts generally capped around 20 kt due to increased stability from the hot air mass. There will be a chance for thunderstorms over Lake Huron on Tuesday as the front lifts through, but confidence is low on timing. Areas of fog may develop over the cooler open waters as well. Additional storms will be most likely to occur near northern Lake Huron where the stability is weakest this week.

CLIMATE...

Daily Records for the Upcoming Week...

Detroit Record High Record Warm Minimum Mon June 29 96 (1933) 77 (1945) Tue June 30 96 (1931) 76 (2018) Wed July 1 98 (1931) 80 (1931) 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 Mon June 29 100 (1934) 75 (1945) Tue June 30 98 (1933) 76 (2018) Wed July 1 102 (1931) 72 (2018) 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 Mon June 29 100 (1971) 75 (1971) Tue June 30 99 (1964) 77 (2018) Wed July 1 103 (1931) 78 (1931) 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 from noon today to 8 PM EDT Thursday for MIZ047>049-053>055-060>063-068>070-075-076-082-083.

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