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KEY MESSAGES

- Showers and a few storms today into tonight, including the potential for heavy rainfall and an isolated strong storm late.

- Multiple rounds of showers and storms possible Monday morning into Tuesday. Severe storms are possible.

- Seasonably cold weather returns with frost/freeze concerns midweek.

DISCUSSION

Issued at 409 AM EDT Sun May 17 2026

Pattern Synopsis:

Broad mid/upper-level ridging will slide over the Great Lakes today as an embedded shortwave trough associated with ongoing severe storms across the central Great Plains lifts into the state later this afternoon/evening. Forcing generated by this feature will drive a subtle surface pressure response along the synoptic warm front mixing north across the state later this evening/tonight -- which drapes back much further west to the parent surface cyclone set to track across the Upper Midwest and far northern Great Lakes tonight into Monday. Elongated surface pressure falls will remain overhead Monday as a second embedded shortwave lifts into the region. Stronger, more organized troughing will eject over the southern Great Plains Monday and lift over the Upper Midwest/Great Lakes Monday night into Tuesday, providing more substantial support for an organized surface cyclone that looks to trek across Wisconsin and the U.P. in the early Tuesday morning/Tuesday afternoon timeframe. The attendant cold front is expected to sweep across the state sometime Tuesday with high pressure building into the region behind this Wednesday through the remainder of the work week.

Forecast Details:

Showers/storms today-tonight -- Precip-free weather will persist through most of this morning before chances for rain and a few embedded storms increase through late morning/early afternoon. Cloud cover will increase through the morning hours as leftover convective activity from severe storms this past evening is expected to work across the state. Fumes of instability at best will struggle to support thunderstorms across much of the area as the warm front, and in turn the warm sector, will likely remain south of the area through this afternoon. That said, a few storms cannot be entirely ruled out near the M-55 corridor today. Thunder chances become increasingly likely along and south of M-72 this evening and tonight just north of where the boundary is likely to drape itself, bringing the potential for training heavy showers/embedded storms and heavy rainfall potential. Where this activity lines up later today/tonight, rainfall amounts in excess of 1" are anticipated with localized amounts near 2" possible by Monday morning -- bringing low chances for flash flooding across southern portions of the CWA.

Additional storms/severe potential Monday/Tuesday -- After rain/storm chances diminish tonight, a complex forecast evolution is likely to unfold that is riddled with uncertainty given multiple rounds of convection are possible from early Monday morning through Tuesday -- including the potential for severe storms. A first round of storms will be possible Monday morning as severe storms from the previous day likely work across the Midwest overnight. Forecast soundings out ahead of expected storms display ample MUCAPE (1,000+ J/kg) but little wind shear above 1km, casting doubt on how well storms will sustain themselves as they work into the Great Lakes in the early/mid-Monday morning timeframe. Regardless, a few strong storms could lead to gusty winds -- even if storms aren't surface based as the aforementioned warm front struggles to mix northward due to previously discussed overnight convection.

This potential round of storms only muddies the forecast waters through the afternoon and evening. First, forecast highs have been adjusted down from the mid/upper 80s during the afternoon. With Multiple rounds of showers/storms and associated cloud cover, confidence is decreasing in the warmest temperatures being realized Monday afternoon. That said, there will be an attempt at airmass recovery as the warm front tries to mix north across the area during the day -- enough so that another round of showers/storms will be possible during the afternoon/evening. While there will be the potential for damaging winds, large hail, and low-end tornado chances Monday/Monday night (Day 2 Slight Risk from SPC), it is emphasized that there is high uncertainty in the range of solutions later Monday -- including the possibility that redevelopment does not occur across northern Michigan during daylight hours and stays confined to our south. With latest guidance, the growing forecast concern is that this solution appears more likely than before and precludes stronger public-facing messaging at this time.

Looking beyond, shower/storm chances continue into Tuesday until the front swings through the area -- which may be our best chance to see strong storms over the next few days (Day 3 Slight Risk). To the dismay of many, our recent stretch of warm weather will end abruptly behind this. Afternoon temperatures on Wednesday may struggle to get out of the 40s for many parts of the area. Frost/freeze concerns also return as forecast lows Wednesday night dip well into the 30s for many interior areas of northern Michigan. This appears to be short lived, however, as temperatures look to gradually warm through the end of the week.

AVIATION /12Z TAFS THROUGH 12Z MONDAY/

Issued at 644 AM EDT Sun May 17 2026

VFR conditions are expected across most of northern Michigan through this afternoon. Rain-free weather will persist through this morning before showers and a few storms work across the area this afternoon. Best rain chances through 00Z Mon will stay south of the bridge with lesser chances (20-30 percent) at CIU. Clouds will increase through the day as rain/storms approach from the southwest. While CIGs will lower with time today, MVFR CIGs look to hold off until after 00Z Mon for most areas. The most likely potential exceptions to this would be MBL and TVC. Widespread MVFR/IFR conditions are likely this evening and tonight as rain coverage increases. LIFR conditions are also possible across interior northern lower tonight. With winds quickly increasing off the surface tonight, low-level wind shear is included in the MBL and TVC TAFs.

APX WATCHES/WARNINGS/ADVISORIES

MI...None. MARINE...Small Craft Advisory from 11 PM this evening to 8 PM EDT Monday for LMZ323-342-344>346. Small Craft Advisory from 8 PM this evening to 8 PM EDT Monday for LMZ341. Small Craft Advisory from 11 PM this evening to noon EDT Monday for LSZ321-322.