Area Forecast Discussion

KEY MESSAGES

- Widespread rain showers continue across the eastern half of the UP this morning. Additional rainfall amounts of 0.10-0.25in are most likely, but there is a 30% chance for higher amounts up to a half an inch.

- A Wind Advisory is in effect for Northern Houghton and Keweenaw Counties this afternoon. Strong westerly winds with frequent gusts of 45+ mph are likely (60-90% chance).

- Gale Warnings remain in effect for the Upper Great Lakes through the early evening. Southerly gales 35-40 kts turn westerly by early Tuesday afternoon. Westerly gusts 40-45 kts will be common with a few Storm force gusts to 50 kts possible (up to 50% chance) near the Keweenaw Peninsula.

- Strong winds create dangerous swimming conditions along the Schoolcraft and Alger County shorelines through this evening.

DISCUSSION

Issued at 158 AM EDT Tue Sep 15 2026

Latest water vapor imagery shows quite nicely the midlevel low currently moving over Manitoba, with deep 994mb low pressure analyzed at the surface and a trailing occluded front draped over the Dakotas. RAP analysis places the UP beneath a strong 40-60kt southerly LLJ, and resulting isentropic ascent has been able to kick off a batch of widespread showers (with some embedded thunder). Showers have moved out of the western half of the UP, and are currently moving through the eastern UP. MRMS shows a widespread 0.10-0.25in over the past six hours over the western UP, with some higher embedded amounts around 0.50-0.75. This is corroborated by available surface observations, and similar amounts are expected over the eastern UP before showers largely wrap up around 12Z.

Apart from the rain, gusty winds are the other main concern of the short term forecast period. So far tonight, under southerly flow, we aren't quite tapping into the strongest winds aloft. Still, some 20- 30mph gusts have been realized tonight, particularly over the eastern UP and in the downsloping areas over the higher terrain and downsloping areas over the north-central UP. Breezy conditions continue the rest of the night. As we head into the daytime hours, the surface low moves towards Hudson Bay and the attendant frontal boundary will press through the region during the late morning to early afternoon hours, veering winds to the west. Strong pressure rises upwards of 1-2 mb/hour and modest upper level cold air advection will work to increase wind gusts on Lake Superior and in the Keweenaw between 40-50 mph with occasional gusts to 55 mph should mixing be able to tap into higher gusts aloft. Elsewhere throughout the UP, expect wind gusts of 20-35mph to be more common. A Wind Advisory continues for N Houghton and Keweenaw Counties from 15-00z Tuesday (10a-8p local).

Moving into the rest of the week, expect generally quieter weather as zonal flow in the upper levels and shortwave ridges moving through the U.P. generally keep active weather away. While this should keep temperatures fairly seasonable for the rest of the week, this does also support dry weather through at least midweek. Wednesday night, latest guidance brings some weak shortwave action to the area, with some low-end rain chances. As the ridge begins to shift eastward towards the weekend and another system moves out of the Plains, better rain chances finally work in by Friday night, and this could be accompanied by another period of elevated wind speeds. That said, there is some disagreement on the precise track and timing of this next system.

AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/

Issued at 107 AM EDT Tue Sep 15 2026

A frontal system moving through Upper Michigan will bring MVFR to IFR conditions with rain and gusty south winds through early this morning. Low level wind shear concerns will abate at the terminals after 08z as a 50 kt LLJ shifts into the eastern UP. Rain departs to the east later this morning, yielding a gradual improving trend back to VFR through 18z. Winds will shift westerly behind a trailing cold front later today and continue to gust to 25-30 kt into the afternoon, perhaps as high as 40-45 kt at KCMX. Winds diminish below 10 kt after 00z Wed under clearing skies as high pressure begins to build into the region.

MARINE

Issued at 158 AM EDT Tue Sep 15 2026

Lake Superior: Strong southerly winds persist tonight as a deepening surface low currently over Manitoba continues northeast towards northern Ontario. Southerly wind gusts up to 35-40kts are becoming more common over the eastern half of the lake. By the late morning to early afternoon, the system's cold front will traverse the lake, veering winds to the west. Given strong pressure rises and increase cold air advection, westerly winds are expected to increase between 35-45 kts for much of the lake. There is a 50-60% chance for a few Storm force gusts to 50 kts around the Keweenaw. Have maintained Gale Warnings for dual directional gales through Tuesday evening. Westerlies fall below 35 kts after 00Z and continue diminishing overnight through Wednesday.

Northern Green Bay and northwestern Lake Michigan: Strong southerly flow persists the rest of tonight into Tuesday morning, with gales to 35kts. As winds turn westerly behind a cold front from mid morning to early afternoon, winds fall below 25 kts and continue diminishing to 15 kts or less through the evening.

MQT WATCHES / WARNINGS / ADVISORIES

Upper Michigan... Wind Advisory from 11 AM this morning to 8 PM EDT this evening for MIZ001-003.

Lake Superior... Gale Warning until 8 AM EDT this morning for LSZ249.

Gale Warning from 8 AM EDT /7 AM CDT/ this morning to 4 PM EDT /3 PM CDT/ this afternoon for LSZ162.

Gale Warning from 8 AM EDT /7 AM CDT/ this morning to 5 PM EDT /4 PM CDT/ this afternoon for LSZ240.

Gale Warning from 8 AM EDT /7 AM CDT/ this morning to 8 PM EDT /7 PM CDT/ this evening for LSZ241>243-263-264.

Gale Warning until 8 PM EDT this evening for LSZ244-245-248- 265-266.

Gale Warning from 10 AM this morning to 8 PM EDT this evening for LSZ246-247.

Gale Warning until 8 PM EDT this evening for LSZ250.

Gale Warning until 9 AM EDT this morning for LSZ251-267.

Lake Michigan... Gale Warning until 8 AM EDT this morning for LMZ221-248-250.