textproduct: Gaylord

KEY MESSAGES

-Storm chances late this evening into tonight with conditional severe threat and hydro concerns. Best chances favor eastern upper and far northern lower Michigan.

-Heat and humidity spike into Monday. Humidity peaks Monday, while air temperatures peak on Tuesday. Potential for 100+ degree temperatures in northeast lower on Tuesday.

-Rain chances return by next weekend.

DISCUSSION

Issued at 328 PM EDT Sun Jul 12 2026

Pattern Synopsis:

Ridging pattern firmly established across the center of NOAM, with significant plume of heat being forced into the Great Lakes with time. Troughing over northeast NOAM will reinforce NW to NNW flow tonight as the warm advection wing associated with the core of the thermal ridge forces its way into the Great Lakes tonight. With N to NNE steering flow, result will be potential for thunderstorm activity to drift in from those respective directions later on as steeper lapse rates yield ample elevated instability, in conjunction with a diffluent flow regime aloft... perhaps giving potential for deep convective processes. Eventually, this wing clears the region, and the heat dials up several notches to kick off the work week. Initial deep moisture plume at the surface will allow for a humid day on Monday as well, before the core of the thermal ridge moves overhead Tuesday. Resulting reductions in dewpoints owing to efficient mixing will lead to potential for rare-tier heat across portions of the region Tuesday. Eventually, anticipating a stationary boundary to force through the region late Tuesday into Wednesday, bringing a reprieve from the heat, but reintroducing rain chances with time.

Details:

Rest of Today / Tonight- Current convective trends have predictably been poorly resolved by any guidance... with CAMs really struggling to get a grip on the evolution of things, even in the 12z suite. A few select models came close with ongoing convective trends over western / central upper Michigan and into Lake Superior. Current subtle trough axis split basically right down the middle of Lake Superior from north to south will continue to be the focus of convection through tonight... and this feature is set to slowly drift SSE through the CWA later this evening into tonight. Ample uncertainty regarding convective evolution... but with increasingly steep lapse rates aloft owing to an EML advecting into the region (pushing 8C/km), anticipating elevated instability to balloon with time tonight, along with increasing shear. As such, there will be the potential for convective complexes to materialize... and with anticyclonic flow in place... could spell a north to south storm motion. Greatest destabilization potential will be later tonight, so if anything goes up, the potential for severe storms will be maximized later tonight. As such, SPC maintains a Marginal Risk of severe storms overhead. Primary concern, of all things, will be large hail... sounding analogs depict some pretty large hail instances, and with ample streamwise vorticity (and reports of large hail west of Marquette already today), certainly believable... and there is potential for significant severe in the event that the environment is fully utilized in any storm development over eastern upper and leaking into northern lower. In addition, largely retrograding / slow storm motion may spell hydrologic / flooding concerns with echo training. Certainly going to have to watch closely, as rapid changes are certainly on the table.

Monday: In the wake of this warm advection wing, anticipating deep moisture pooling to transpire over the region, spiking surface dewpoints to near 70 (some guidance suggests mid-to-upper 70s, but based off current upstream trends, this seems unlikely, even with the lakes contributing moisture). Considering spiking 850mb temps, anticipating a pretty firm cap overhead during the day... and with minimal synoptic forcing to generate a lifting mechanism, should net a dry, albeit hot and humid day Monday. The wild card? Ye Olde Lake Breeze in northeast lower... but conceptually, this feature may be too shallow to completely erode the cap. In the event that the cap can break again Monday, the atmosphere remains primed to produce stronger convection, but increasingly confluent flow aloft suggests a suppression trend that can't be overcome. As such, most of the area likely to spike in the 90s (warmest NE lower and near TVC, along with inland eastern upper... mid-upper 90s on the table in these areas). Coupled with higher dewpoints, heat indices to spike 96 to 103 area-wide. Tightening pressure gradient and accelerating 850mb flow suggest a lack of radiational cooling Monday night... warmer guidance is suggesting widespread lows in the mid-to-upper 70s. Certainly will be a tough stretch for those sensitive to heat illnesses, especially those without adequate cooling. As such, have opted to hoist a Heat Advisory from Monday afternoon through Tuesday morning to cover the overnight conditions as well.

Tuesday heat: Core of the ridge to pivot overhead into the day on Tuesday, with impressive 850mb temps pushing or even exceeding +25C on the table. With the ridge axis basically right overhead, anticipating superb mixing to bring very dry air to the surface, particularly across northeast lower Michigan, aided by downsloping NW winds. Will be a touch of a temperature contrast across the region... generally speaking, the hottest area on Tuesday will be Ne lower, specifically the Saginaw Bay area. If we can completely mix the profile, it is not impossible to see actual air temperatures approach 105F in that particular area aided by downloping warming. Elsewhere, anticipating highs to peak in the mid 90s owing to Lake Michigan moderation, with the exception of the TVC area, which with downsloping into the city proper, likely sees temperatures spike into the upper 90s. Did not run heat headlines through Tuesday owing to the lesser humidity concentration, and thus, less of a disparity between air temperatures and heat indices. Nonetheless, in the warmest areas, purely from air temperatures, it is likely an extension to the advisory will be necessitated.

Rest of the Period: Troughing regime in northeast NOAM to dig and even retrograde westward with time, which will draw in cooler air from the north, but will essentially put the region in the heart of the baroclinic zone between the extreme heat to the south and much cooler northern Canadian air. With the help from some synoptic forcing, this should conceptually spell a wetter close to the week and perhaps into next weekend, amid much more seasonable temperatures.

AVIATION /00Z TAFS THROUGH 00Z TUESDAY/

Issued at 746 PM EDT Sun Jul 12 2026

A line of weakening showers will work into parts of northwest lower Michigan over the next 1-2 hours, potentially reaching TVC and MBL with light rain. However, this activity is working into an increasingly hostile environment and will likely diminish in the next few hours this evening. Very low chances (10 percent or less) exist for showers and storms to move into parts of northern Michigan from Ontario late tonight/early Monday morning. That said, VFR conditions are expected at all TAF sites through the issuance period. Winds look to increase out of the southwest Monday morning and gradually turn to west winds into the afternoon, gusting to 15- 20 kts at times.

APX WATCHES/WARNINGS/ADVISORIES

MI...Heat Advisory from noon Monday to 8 AM EDT Tuesday for MIZ016>018-020>036-041-042-086>088-095>099. MARINE...None.