Area Forecast Discussion

KEY MESSAGES

- Low confidence on any severe thunderstorms tonight into sunrise Monday. If storms maintain strength into our area, damaging wind gusts are the primary hazard.

- Improved confidence in severe thunderstorms Monday afternoon and evening. Damaging wind gusts are the primary hazard. Tornadoes cannot be ruled out.

- Hot on Monday with highs near 90s and an afternoon heat index approach 100 for western northern Indiana.

- Dangerous waves and currents expected on Tuesday at southeast Lake Michigan beaches.

DISCUSSION

Issued at 235 PM EDT Sun Jul 26 2026

Filtered sunshine this afternoon now that morning stratus has mixed out; more humid as well with dew points in the low-70s. All eyes on the upper Great Lakes this afternoon where thunderstorms are underway in extreme northwest Minnesota. As to be expected, CAMs this morning have varied wildly run-to-run regarding the evolution of upstream storms these next 24 hours. The general concensus is that embedded mid-and-upper level disturbances passing through energetic northwesterly flow will spark afternoon and evening thunderstorms over the upper Midwest today. Storms then spill SSE atop a strong ridge in the lee of the Rockies. This track generally keeps the most robust thunderstorms over Wisconsin and Illinois tonight, but there are intermittent runs that send a decaying complex of storms through west-Central Michigan.

With fading instability tonight, waning bulk shear values, lagging upper-level support, and a weakening rise/fall couplet on pressure- change plots, there is medium-high confidence that upstream activity weakens as it perhaps limps into to the western- third of the forecast area after midnight. Alternatively, it could be dry all night given the best forcing is well north. Also uncertain is whether or not a second complex of storms can quickly develop tonight over WI, drifting in locally after sunrise Monday. Some CAMs have these two complexes comically close to one other, raising significant questions about how quickly the atmosphere could recover. We'll retain some POPs Monday morning to account for this possibility, but confidence is low for severe storms tonight through sunrise Monday.

Monday afternoon and Monday night is our best opportunity for severe thunderstorms capable of producing damaging wind gusts. An approaching 50-60 knot 500-mb jet dives in by late afternoon, likely sparking storms over southern WI or central MI which organize and drop south through our area. Severe weather parameters remain favorable, including enhanced areas of SRH, introducing a chance for embedded tornadoes. Any morning activity will directly impact how the afternoon evolves, but the current timing of 2pm to 2am Monday appears on track. Hot on Monday as well with highs near 90, especially in the western half of northern IN. Afternoon heat indicies will approach 100 degrees, but the possibility of cloud debris and thunderstorms limits confidence in any heat- related headlines.

Not as hot the rest of the week as troughing and surface high pressure settle over the eastern Great Lakes. High pressure softens toward next weekend, introducing the chance for showers and thunderstorms.

AVIATION /00Z TAFS THROUGH 00Z TUESDAY/

Issued at 726 PM EDT Sun Jul 26 2026

The area is in a sort of suppressed (read: subsidence) pattern as a stronger shortwave departs to the east of the area and only weak shortwaves attempt to round closer to the height max of the ridge. It is possible that convection forms over the Upper Mississippi Valley forms around 6z and approaches the area from the north/northwest between 12 and 15z Monday with ample shear and around 1500 J/kg of MUCAPE. On the other hand, there appears to be a low pressure system that approaches during the early afternoon, Monday, and that may be enough to set off thunderstorms during afternoon. As such, will still keep a mention of thunderstorms for the 12z time Monday out and there is a model camp for around 00z Monday evening for thunderstorms, but that's at the end of this TAF period so will leave that out as well. Additionally, will keep VFR conditions in place with southwest winds prevailing and sustained 10+ kts winds during Monday afternoon.

IWX WATCHES / WARNINGS / ADVISORIES

IN...None. OH...None. MI...None. MARINE...None.