textproduct: Detroit/Pontiac

KEY MESSAGES

- The Heat Advisory has been extended until Wednesday evening for max heat indices in excess of 100F.

- EGLE has declared an Air Quality Alert for Wednesday due to encroaching Canadian wildfire smoke reaching the surface and the resultant rise in PM2.5.

- A few isolated non-severe thunderstorms are possible late Wednesday afternoon.

- A gradual cooldown begins Thursday with periods of showers and thunderstorms from Friday into early next week.

DTW THRESHOLD PROBABILITIES

* Low for thunderstorms Wednesday evening.

PREV DISCUSSION

Issued at 341 PM EDT Tue Jul 14 2026

DISCUSSION...

Broad ridging expands to encompass most of the northern half of CONUS today. Geopotential heights associated with the anomalous ridge maximize this afternoon, marked by 500 mb heights of 600 dam centered along the Minnesota/Iowa border. Temperatures have responded accordingly to the stable and subsident airmass as readings largely peak into the mid to upper 90s. Given a cool start this morning and some high cloud debris, adjusted highs and heat indices downward by a degree or two, but still within Heat Advisory criteria. Radiation cooling and a slight reduction in dewpoints should allow temperatures to drop into the low to mid 70s tonight offering brief relief from the heat.

The longwave ridge will flatten and weaken Wednesday as a speed max moves into the base of a Hudson Bay upper low. This should lead to a slightly cooler day, but still very hot and humid as highs return to the mid to upper 90s, with dewpoints in the 70s, mixing lower through the afternoon. In combination, another round of max heat indices above 100F is likely. One caveat to the temperature forecast for Wednesday is that central Canadian wildfire smoke will get advected into northern Lower Michigan by the unbound shortwave, eventually directing the plume into southern Lower by mid-morning. This should have a net cooling effect on the diurnal curve and warrant possible downward revisions to forecast temperatures, but unless smoke density vastly overachieves, conditions are still ripe for the persistence of Heat Advisory criteria through Wednesday evening. Added CWA-wide smoke wording to the latest NDFD grids.

In terms of precipitation potential, cannot completely rule out a couple isolated pop-up thunderstorms given resultant surface CAPE, a reduction in the capping inversion strength, and a weak low-level frontal/convergence boundary. Latest PoPs reflect a slight upward adjustment, but still below 25 percent (Slight Chance), given continued ambient column dryness and weak forcing aloft. Should any storms materialize between I-94 and M-59, severe weather is not expected. A lake breeze boundary could also suffice in forcing a stray storm or two later in the day. CAMs suggest CI would be unlikely prior to 3 PM. Uncertainty exists as to any persistence of convection into the early overnight period, but unlikely for anything after midnight.

Height falls continue over the state on Thursday as the eastern North America longwave trough slowly digs eastward. This leads to 500 mb geopotential height reductions AOB 590 dam. Still hotter than normal Thursday with highs mainly in the low 90s, but dewpoints should hold below 70F making for headline-free heat. This marks the start of a gradual cooldown Thursday, taking until sometime next week for readings to return to near-normal. During the cooldown period, frequency of showers and thunderstorms will be on the rise, with the first round on Friday as Gulf moisture lifts into the Ohio Valley beneath perturbed flow.

MARINE...

A hot airmass remains in place today over the Central Great Lakes, leading to stable low level profiles. This should hold west- southwesterly wind gusts below 25 knots for the rest of today, mainly across the northern third of Lake Huron and Saginaw Bay. A weak backdoor front drops south tonight into Wednesday allowing winds to eventually veer to the northwest behind the front. Winds still only top out around 20 knots Wednesday evening over the north half of Lake Huron. A couple pop-up storms are possible along lake breeze development. Northwest winds at or below 20 knots holds on Thursday. Lower confidence forecast for Friday and Saturday due to conflicting model guidance regarding the location and magnitude of a surface low moving through the Great Lakes region. This has significant impact not only on wind speeds, but also on wind direction, along with bringing chances of showers and thunderstorms.

DTX WATCHES/WARNINGS/ADVISORIES

MI...Heat Advisory until 8 PM EDT Wednesday 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.