textproduct: Detroit/Pontiac

KEY MESSAGES

- Heat builds during the early half of the week with highs in the 90s Monday through Wednesday.

- Peak heat expected Tuesday with highs in the upper 90s and heat indices near or above 100 degrees.

- Potential for showers and thunderstorms exists late in the week into next weekend.

DISCUSSION

1023 mb surface high pressure is entrenched overhead this afternoon, which has led to another day of dry and seasonable mid-July weather for SE Michigan. Fair weather cumulus is observed extends from the Thumb into northern OH/IN in the anticyclonic flow pattern, but is shallow and ultimately expecting a dry and pleasant evening for SE Michigan.

Instability bubble is still confined to the U.P./Upper Midwest, but will gradually pivot around the ridge and into Lower MI early Monday morning. There are some model solutions (the most aggressive being the HRRR) that initiate convection over central Ontario and send it south toward the progressing instability plume overnight. Given that instability is already being worked over by Lake Superior convection at issuance, do not think this convection will be able to survive into central/southern MI for very long. Slight chance PoPs however bump against the northern border of our cwa Monday morning as a result.

Heat begins to build across the state Monday, with the hottest conditions arriving Tuesday as a 600 dam mid-level ridge stalls over the Upper Midwest. Downsloping effects over the Saginaw Valley and metro Detroit (plus urban effects) will lead to a local boost in highs by a couple of degrees. So while most locations see highs in the mid-upper 90s, high temperatures in these locations will be closer to 100. Heat indices remain in the 100-105 range at best given sub-par moisture quality as dewpoints barely reach 70 degrees Tuesday, which may require a Heat Advisory. Overnight lows then remain seasonably warm, in the low-mid 70s through Wednesday morning. The ridge establishes a strong capping inversion that limits thunderstorm chances for the first part of the work week.

In contrast to our last heat stretch, this one will be shorter-lived with the ridge breaking down mid-week and folding into SE CONUS as a strong low carves into Quebec. This leads to a period of height falls Wednesday and a flip in column winds from NE to NW, while also establishing a deformation axis across northeast CONUS/Canada late in the week. Higher confidence item in this pattern is a drop in temperatures closer to normal: upper 80s-low 90s by Thursday. Much lower confidence in thunderstorm chances though, which will depend on how the deformation axis behaves. Nebulous signal in the ensemble guidance is due to the variability in individual members, ranging from aggressive high pressure pushing all moisture/instability into the Ohio Valley to a surge of return flow/instability into the Great Lakes for the end of the week. About 15% of ensemble members have no instability building into the region until next weekend, although most stall the instability axis north of the state line. To sum it up, the pattern late week-next weekend is low confidence and unsettled when it comes to rain/storm chances.

MARINE

High pressure will continue to hold over most of the Great Lakes region today and going into the beginning of the week. The one caveat will be across northern portions of Lake Huron where there will be a slight chance for showers and storms this evening going through the overnight hours. Any precipitation will diminish by early Monday morning and dry conditions will prevail though much of the week. Lighter northeast winds will continue to be variable as the high passes overhead this afternoon before becoming more southerly going through the evening.

PREV DISCUSSION

Issued at 1253 PM EDT Sun Jul 12 2026

AVIATION...

High pressure extends from the central Plains to the southern Great Lakes to the New England states today and is projected to hold a similar position tonight and Monday. The result is VFR under a shallow cumulus response to daytime heating with light lake breeze augmented easterly wind this afternoon and evening. Northern Great Lakes thunderstorms are not expected to survive the attempt to propagate through northern Lower Mi tonight, although mid/high debris clouds likely reach the MBS to FNT area. Light and variable to calm wind carry the rest of the way through sunrise followed by a light SW component Monday.

D21/DTW Convection...No thunderstorms are forecast.

DTW THRESHOLD PROBABILITIES...

* None.

DTX WATCHES/WARNINGS/ADVISORIES

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