textproduct: Marquette

KEY MESSAGES

- Chilly tonight with frost in the interior west. A Frost Advisory is in effect for several counties of the western UP. Patchy frost is possible elsewhere across the interior central and east.

- Widespread rain moves into the UP from west to east late Monday through Tuesday morning. There is a 40-70% chance for rainfall amounts >0.5", mainly across the southern half of the UP.

- A Gale Watch remains in effect for the Upper Great Lakes Monday night through Tuesday. Southerly gales 35-40 kts turn westerly Tuesday afternoon. Westerly gusts 40-45 kts will be common with a few gusts to 50 kts possible (50-70% chance) near the Keweenaw Peninsula.

- Strong westerly winds are expected Tuesday afternoon, especially in the Keweenaw where frequent gusts near 45 mph are possible (60- 90% chance).

DISCUSSION

Issued at 305 PM EDT Sun Sep 13 2026

Afternoon satellite imagery imagery reveals troughing stretching down from the Hudson Bay down through the Great Lakes. Cold air advection characterized by 850 mb temperatures falling into the single digits has been able to kick off scattered lake effect rain showers for the NE UP. So far temperatures have only managed to peak in the low 60s to upper 50s this afternoon under gusty NW winds. Tonight, lake effect showers dwindle in the east as drier air works into the region. Under mostly clear skies, building high pressure, and diminishing winds, efficient radiational cooling will allow the interior west to cool into the upper 20s to low 30s. Frost Advisories have been expanded for most of the western UP save for the Keweenaw. Elsewhere, patchy frost and upper 30s may be found across the interior central and east, but confidence is lower on frost potential there. Even the lakeshores may be able to enjoy a cool night in the 40s!

Our attention then turns to a period of active weather tomorrow night through Tuesday. High pressure overhead will keep the region dry through most of the day tomorrow, however, widespread rain is anticipated Monday night through Tuesday morning as a deep moves from the Northern Rockies into the High Plains. Moist return flow (PWATs climbing near the 95-99th percentile of climo) and strong isentropic ascent will be the focal point for a wave of showers and maybe a few embedded thunderstorms moving west to east across the UP ending early Tuesday. Ensembles still present some uncertainty regarding QPF amounts and where the greatest amounts will be found. The tail end of this morning's HREF and REFS run suggest a 40-70% chance for rainfall amounts >0.5" largely confined to the southern UP while global ensembles like the NBM and LREF are happy to paint greater probs of >0.5" (60-90%) across the entire region. Regardless, any meaningful rain is welcome to help curtail ongoing drought. Strong southerly winds accompanying a 45-55kt LLJ and pressure falls ramp up late Monday to early Tuesday. Widespread 30- 40 mph wind gusts will be common. NBM and CAM guidance is a little too hot with the upper end of wind gust potential, suggesting favorable probability for 40-45 kt gales on the lakes. Pattern recognition tells us that this is not likely to happen, as mixing into the 45-55 kt LLJ doesn't often occur given early fall over-lake stability. A few gusts >40 kts are possible, but widespread gusts >30-40 kts are hard to achieve in a southerly wind regime. What is more likely to happen is strong westerlies on Lake Superior and in the Keweenaw Tuesday afternoon as pressure rises (~1 mb/hr) and cold air advection contribute to gusts reaching 40-50 kts. Ensembles suggest high probability (60-90% chance) for frequent gusts >45 mph (Wind Advisory criteria) in the Keweenaw.

Zonal flow and height rises contribute to drier and more seasonable weather heading into the mid to late week.

AVIATION /18Z TAFS THROUGH 18Z MONDAY/

Issued at 137 PM EDT Sun Sep 13 2026

VFR conditions continue through the forecast period, with high ceilings and no visibility limitations. Some lake effect showers are ongoing over southeastern Lake Superior. SAW may see a very brief, light rain shower or two this afternoon if a shower strays inland, but confidence is too low for inclusion in the TAF. Winds are expected to remain gusty and northwesterly this afternoon, reducing to ~5kts overnight as a high pressure center moves across the U.P. Monday morning, winds will increase to ~10kts and become southerly on the back side of the high pressure center.

MARINE

Issued at 305 PM EDT Sun Sep 13 2026

Lake Superior: Gusty W to NW winds 20-30 kts have been common through this morning and afternoon with a few gales to 35 kts mixed in at Stannard Rock and Granite Island. Building high pressure will act to weaken winds back down to 20 knots or less again tonight and to remain that way until Monday afternoon. As a warm front approaches the area on Monday, expect the winds to increase from the southeast and south ahead of it later in the day, with southerly gales of 35 to 40 knots being seen across the east half of the lake Monday night. A few southerly gales 40 to 45 knots may be realized if mixing can tap into a 45-55 kts low level jet, but pattern recognition tells us that this is hard to achieve in a southerly wind regime in the early fall given over lake stability. Winds veer westerly behind a cold front Tuesday morning. Strong pressure rises and cold air advection will work to increase west gales of 40 to 45 knots across most of the lake, especially closer to the Keweenaw Peninsula where there is a 60-90% for gales between 45-50 kts Tuesday afternoon. As a flattening high pressure ridge begins to move into the area for the middle of the week, expect the winds to weaken back down to 20 knots or less by late Tuesday night, remaining that way until potentially next weekend.

Northern Green Bay and northwestern Lake Michigan: WNW winds of 15 to 25 knots this afternoon fall back down to 15 knots or less again late tonight. The lighter winds remain until an approaching warm front on Monday increases winds from the south during the afternoon hours. As the front occludes Monday night, expect the southerly winds to become maximized to gales near 35 to 40 knots. In addition to the gale potential, some rumbles of thunder could be heard during the overnight hours. However, no severe weather is expected. While cold air advection does work into the area on Tuesday, with the better CAA over Lake Superior, expect the winds to slowly dwindle with time as they veer, eventually becoming 15 knots or less again Tuesday night as flattening high pressure ridging builds into the Upper Great Lakes.

MQT WATCHES/WARNINGS/ADVISORIES

Upper Michigan... Frost Advisory from 2 AM EDT /1 AM CDT/ to 9 AM EDT /8 AM CDT/ Monday for MIZ002-004-009>011-084.

Beach Hazards Statement until 9 PM EDT this evening for MIZ006.

Lake Superior... Gale Watch from late Monday night through Tuesday afternoon for LSZ162.

Gale Watch from Monday evening through Tuesday evening for LSZ240>251-263>267.

Lake Michigan... Gale Watch from Monday evening through Tuesday morning for LMZ221-248-250.