569
FXUS63 KMQT 170525
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
125 AM EDT Tue Jun 17 2025

.KEY MESSAGES...

- Strong or severe storms are possible (5-15% chance) this
  evening across western Lake Superior and the west half of
  Upper Michigan. Damaging winds and large hail are the primary
  risks.

- Shower and thunderstorm chances return Wednesday into
  Wednesday night, mainly for the central and east thirds of
  Upper Michigan. Scattered showers/storms expected Thursday
  across Upper Michigan.

- Near normal temperatures this week trend above normal by late
  this coming weekend.

&&

.UPDATE...
Issued at 1134 PM EDT Mon Jun 16 2025

The solution indicated by most of the CAMs is playing out this
evening: the line of convection that was able to track through MN
split as it reached western Lake Superior. With the low moving
across the western arm of the lake, an area of more stratiform-
looking rain and embedded thunder is moving through the Arrowhead.
Stronger convection dropped into the more favorable environment
across western WI. In between, we`re only seeing a few spotty
showers and some thunder reaching the far western UP. Will allow
chance pops to sweep through the rest of the area overnight as the
low tracks across northern Lake Superior and the associated cold
front moves through our area. However, with better forcing outside
of our area and increasingly stable conditions into the second half
of the night, confidence in any stronger convection across our neck
of the woods is low.

&&

.SHORT TERM /THROUGH TUESDAY NIGHT/...
Issued at 226 PM EDT Mon Jun 16 2025

Partly to overcast skies have, more or less, sat over the forecast
area today under light, southerly flow. What appeared to be a
gravity wave pressing through the region around mid-morning helped
kick off weak showers over parts of the interior west and east, but
overall, Upper Michigan has been mostly dry so far. Temperatures
have warmed into the 70s so far with dewpoints in the muggy 60s to
upper 50s. Upstream, a surface low reinforced by a shortwave in
western Minnesota/Dakotas supported showers and thunderstorms
earlier. These waned some but recently began to reorganize.

For the remainder of the afternoon, destabilization to 1000-2000 j/kg
MUCAPE with overall weak isentropic ascent and deep layer 0-6km
shear near 30kts may support isolated to scattered showers
developing, perhaps mixed in with a rumble of thunder across mainly
the interior western half. Outside of this, mostly dry conditions
are expected for the rest of the afternoon.

Upstream in Minnesota where there`s better forcing, thunderstorm
activity is expected to increase as the surface low presses eastward
toward Duluth and the Arrowhead. Near 0-2z CAMS suggest a line of
thunderstorms will press into Lake Superior, then separate into 2
clusters as they approach western Upper Michigan thereafter. The
southern segment looks to dive southeastward along the state line
while the northern segment presses east-northeast toward Isle
Royale/Thunder Bay. There are still some outlier models suggesting
the system holds together, but this is appearing to be increasingly
less likely given the weakening trend of these storms due to
decreasing instability and only modest shear. However, initially,
there is a small window where enough instability and shear could
support strong to severe thunderstorm activity within the southern
segment. Main areas for severe potential continue to be western Lake
Superior, western Upper Michigan, and south-central near the WI/MI
state line. If something is able to get going and then maintain
itself into our forecast area, strong to damaging winds and hail to
1 inch would be the main severe weather risks. Outside of this,
strong storms may be embedded within the cluster moving toward Isle
Royale/Thunder Bay this evening. Thunderstorm activity may continue
after midnight, mainly in north-central Lake Superior, south-central
and eastern Upper Michigan, but the storms will weaken through the
night.

By Tuesday morning, the surface low is expected to be near Isle
Royale. There may be precip closer to the low, as well as scattered
showers/storms in the east, but these should end by mid-morning.
Tuesday appears to be mainly dry afterwards. Daytime highs look to
warm to near 70 by Lake Superior and mid 70s to low 80s elsewhere.
Tuesday night also looks to be dry. Overnight lows look to fall
mostly into the 50s.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
Issued at 226 PM EDT Mon Jun 16 2025

Weak, quasi-zonal flow Wednesday will stretch across the Northern
Tier, sitting atop broad troughing and multiple shortwaves across
central CONUS. At the surface, a cold front will stretch southwest
from southern Ontario/Lake Huron into the middle-Mississippi River
Valley. Upper level forcing from the initial shortwave will support
showers and thunderstorms in Iowa/Illinois/Missouri early Wednesday.
As the day evolves, this wave lifts northeast and stretches into the
Upper Great Lakes along the aforementioned frontal boundary. Past 24
hours of EC/GEFS ensemble guidance has resulted in tighter
clustering of surface low locations as it tracks northeast. There is
still some spread though, which is reflected in the timing
differences in the deterministic suites. Overall though, these
continue to suggest the greatest potential for showers/thunderstorms
will be over the central and eastern portions of the forecast area.
Temporally speaking, there has been a little better focus on
activity being late morning to evening hours central and late
afternoon potentially into Thursday morning in the east. Between the
LREF and NBM, probability of exceeding 0.5 inches of QPF range from
25-50% in these locations, with less in the west, which values there
generally represent the ensemble outliers. Upstream in
Ontario/Manitoba/Northern Plains Wednesday, a cold front is expected
to press southeastward, moving into the forecast area on Thursday.
This front will swing through Upper Michigan Thursday afternoon and
evening, likely resulting in scattered showers and thunderstorms
across the region.

Upper level ridging builds into the Central Plains Friday while a
surface high stretches into the Upper Great Lakes. This largely
looks to keep us dry through the day. However, a ridge roller
pressing eastward along the ridge top will press eastward through
the day. Guidance continues to highlight this pressing into Upper
Michigan Friday evening/early Saturday. Afterwards, the ridge will
shift southeast into the South while a deep trough presses through
the Rockies. This will result in an amplified trough/ridge pattern
across CONUS. The first wave/warm front ejecting out of the trough
may move through the region Sunday.

Temperatures in this forecast period are largely expected to trend
upwards in time, with near normal temperatures becoming above
normal. Expect 60s and 70s to become widespread mid 80s by Sunday as
dewpoints climb into the upper 60s. Overnight lows follow the same
pattern, with 40s and 50s becoming widespread 60s by Sunday night.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 125 AM EDT Tue Jun 17 2025

Spotty showers continue to develop around IWD and CMX tonight,
though the thunderstorm threat has come to an end. Ample lower level
moisture has already brought ceilings down to MVFR at IWD, with
ceilings falling to MVFR at CMX over the next couple of hours and to
IFR into the early moring. Some MVFR/IFR fog will also be possible
at CMX. At SAW, MVFR ceilings settle in Tuesday morning. Low level
jet moving over the area tonight may also support modest LLWS at
SAW. An improvement to VFR is expected at all terminals Tuesday
afternoon.

&&

.MARINE...
Issued at 259 PM EDT Mon Jun 16 2025

A marginal risk continues for severe wind gusts up to 34 knots and
hail up to 1 inch over the far western waters this evening/tonight.
Outside of any thunderstorms, southerly winds will also gust up to
20 to 25 knots tonight through tomorrow, eventually becoming
west-southwesterly in the wake of a cold front. In addition,
patchy dense fog <1mi will remain a threat tonight as well over
the west half of the lake (40-50% chance). West-southwesterly
winds will gust to 20 to 25 knots through early Tuesday
afternoon before finally falling below 20 knots. At that point,
light and variable winds will prevail into Thursday when gusts
in the 15 to 20 knot range return through the weekend.

&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
  Dense Fog Advisory until 8 AM EDT /7 AM CDT/ this morning for
     LSZ162-263-264.

Lake Michigan...
None.

&&

$$

UPDATE...
SHORT TERM...JTP
LONG TERM...JTP
AVIATION...LC
MARINE...TDUD