Keweenaw Bay, Michigan Weather Forecast Discussion

828
FXUS63 KMQT 210510
AFDMQT
Area Forecast Discussion
National Weather Service Marquette MI
110 AM EDT Sun Sep 21 2025
.KEY MESSAGES...
- Off and on showers and thunderstorms are expected through
  early next week.
- Seasonable temperatures continue through next week.
&&
.DISCUSSION...
Issued at 218 PM EDT Sat Sep 20 2025
Afternoon water vapor and RAP analysis show a negatively-tilted
midlevel trough digging into SW WI, and an additional shortwave
moving into North Dakota. An occluded front from central MN to
southern WI. Ahead of the more southerly shortwave, drier midlevel
air is seen across much of WI and into the UP, which has helped to
cut down on the coverage of showers and storms over the area. Still,
some spotty convection continues to develop over the LP, Lake
Michigan, and northern WI at times - perhaps due to some subtle
shortwave action ahead of our main feature(s) of interest. These are
not particularly high-impact, but still carry a potential for
isolated thunder this afternoon. Otherwise, we remain under mostly
cloudy skies with temperatures already rising comfortably into the
lower-mid 60s. Especially where we can get some breaks of clouds,
some spots may climb higher into the upper 60s this afternoon.
Meanwhile, with a fairly tight pressure gradient in between our
troughing and the surface high over Quebec, SSE winds remain
elevated over the eastern UP and to a lesser extend more westward;
expect gusts up to 20mph the rest of today.
The trough over WI continues to move towards the UP tonight, with
the aforementioned frontal boundary over southern WI lifting
northward as a warm front. This results in a more notable increase
in shra/tsra coverage for tonight; strong to severe storms are not
expected with limited CAPE and shear. Additional rain totals range
from a trace to a tenth of an inch for most of the area, but higher
amounts between 0.25" and 0.75" is expected with any heavier
downpours tonight. As the additional upstream shortwaves cycle
through the region on Sun and Mon, further widely-scattered
shra/tsra are expected. Instability will be higher, but the amount
of wind shear available is still quite limited, so severe weather is
not expected. With ample low level moisture present (especially
where precip occurs during the day) and calm winds overnight, patchy
fog is expected Sun night and Mon night. Expect mild weather to
persist with highs in the 60s to lower 70s and lows in the 50s.
From there, high pressure builds in from the N through Wed
afternoon. Sct diurnal -shra are possible on Tue, but are not
currently reflected in the fcst at this time. Confidence in the fcst
breaks down Wed onward as models continue to struggle to resolve the
closed low likely to develop. This initiates as a deeper trough
making landfall on Sun over the PAC NW late today into Sun. This
trough progresses over the Rockies on Mon then moves out over the
Plains on Tue. From there it is uncertain how this wave will
interact with the last lingering shortwave over the Upper Midwest
and a ridge building over the NW CONUS. This will have implications
on the sfc pattern and impact how dry the remaining portion of the
week is. The latest GFS and NAM (now that it`s available that far
out) quickly form the closed low by late Tuesday. While the NAM then
brings this farther south towards the mid- or lower-Mississippi
valley, the GFS keeps it along with its sfc low well within the
Great Lakes region, yielding a much wetter solution compared to the
ECMWF and Canadian. Those two models struggle to develop a closed
low or keep the feature well to the S, leaving only slight chances
for diurnal shra in the fcst early on. The NBM was left as is after
Mon given the uncertainty, which favors dry weather until next
weekend with a passing cold front. Otherwise, temps by and large
stay consistent the entire fcst with highs in the mid 60s to low 70s
and lows in the 40s and 50s.
&&
.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 109 AM EDT Sun Sep 21 2025
Anticipate fluctuation between MVFR and VFR to continue at all TAF
sites early this morning with an upper level low over the region.
Moisture continues to stream into the TAF sites along with periods
of scattered showers and isolated thunderstorms, those of which are
expected to become more widespread by this afternoon. Best way to
highlight such intermittent showers/isolated thunderstorms continues
to be tempo and prob30 groups for periods of MVFR/IFR and even
possible LIFR/VLIFR conditions at SAW by Sun 09Z.
&&
.MARINE...
Issued at 218 PM EDT Sat Sep 20 2025
Easterly winds over the western third of the lake are coming in at
around 15-20 kts with east to southeast winds between 20-30 kts over
the remainder of the lake through this tonight. This results in
significant wave heights of 4-6 ft over the north central portion of
the lake and along the international border waters today. Winds
gradually settle below 20 kts from W to E through Sun morning,
likely remaining below 20 kts through much of next week. Otherwise,
expect on and off showers and thunderstorms through early next week.
&&
.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
None.
Lake Michigan...
None.
&&
$$
DISCUSSION...LC
AVIATION...TDUD
MARINE...LC

NWS MQT Office Area Forecast Discussion