012
FXUS63 KMQT 212006
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
406 PM EDT Sat Sep 21 2024

.KEY MESSAGES...

- The prolonged stretch of above normal temperatures ends today,
  with temperatures cooling near normal Sunday.

- A round of showers and storms accompany a cold front tonight
  through Sunday. Severe weather is not anticipated, but some
  small hail are possible with stronger storms.

- Showers end from west to east through Sunday as the cold front
  exits the UP. Gusty NW winds behind the front, with the
  highest gusts along the eastern shores of Lake Superior up to
  30 mph.

- Other than a slight chance (15-20%) of showers associated
  with a low pressure passing through Lower Michigan Tuesday,
  dry weather is expected this week.

- Patchy frost potential (~20%) for typical cold spots of
  interior western Upper Michigan Monday and Tuesday morning.

- Supportive setup for patchy fog (~20%) each morning next
  week.

&&

.SHORT TERM /THROUGH SUNDAY NIGHT/...
Issued at 321 PM EDT Sat Sep 21 2024

Latest water vapor imagery shows a well-defined shortwave trough
lifting northeast into northern Ontario and northern MN this
afternoon. This shortwave trough will move into the Upper Great
Lakes later tonight and Sunday, sending a sfc cold front across
Upper Mi tonight into Sunday morning. WAA and a 40+ kt LLJ max ahead
of the cold front have already supported showers and scattered t-
storms early this afternoon into north central WI and portions of
western Lake Superior. A few showers may have made it into far
western Upper Mi but showers have generally dissipated moving into
into ridging and the associated dry and stable air mass across Upper
Mi. While it`s been more cloudy into western Upper Mi due the
convection drifting into that area, ridging has supported more
sunshine into central and eastern areas of the U.P. this afternoon.
Afternoon temperatures have generally been in the 70s to lower 80s,
warmest inland east and coolest west under the clouds.

Heading into this evening and tonight, the vort max/shortwave will
continue to lift northeast through northern Ontario which will send
the mid-level trough axis across Upper Mi later tonight into Sunday.
As the system`s associated cold front moves across Upper Mi tonight
into Sunday morning, showers along the cold front will most likely
move into far western Upper Mi early this evening and then spread
into central Upper Mi late evening and eastern Upper Mi overnight.
Instability along the front is not particularly impressive,
generally 500 j/kg MUCAPE, with the best of that south along the WI
border. Effective shear along the front when showers will be
occurring also generally looks like it will be 30 knots or less, so
not really expecting any severe storms, but maybe a stronger storm
with some dime-sized hail could develop south central along the WI
border where marginal instability and shear appear to be maximized.
Look for min temps lowering into the 50s behind the cold front
tonight. Northwest winds behind the front could gust near 30 mph
late tonight/early Sunday along the tip of the Keweenaw.

&&

.LONG TERM /SUNDAY THROUGH SATURDAY/...
Issued at 404 PM EDT Sat Sep 21 2024

A cold front exiting the UP to the east Sunday will signal the
departure of the best chances of precipitation for the next week
ahead. A Colorado Low-style shortwave will phase with an Alberta
Clipper-style shortwave over the southwestern extent of the Midwest
Monday into Tuesday and the resulting surface low will pass through
the Lower Peninsula of Michigan Tuesday, resulting in most of the UP
staying high and dry. 500mb ridging then builds in behind the
departing trough Wednesday into the weekend and while the details
are uncertain (and could be complicated by any potential tropical
development), another blocking pattern could bring up to 50% chances
of an extended period of drier than normal weather into October.

For Sunday, showers and thunderstorms will be ongoing in the morning
hours across central to eastern Upper Michigan. Showers should exit
the CWA by 02Z Monday, though not before bringing an additional
quarter to half inch of rain to the eastern third of the UP. Despite
meager surface instability, HREF reflectivity paintball plots still
show some isolated to scattered thunderstorm potential with the
showers, so slight chance to chance thunder (15-30%) has been kept
in the forecast, though no severe weather is forecast. Winds look to
be gusty behind the front especially over Lake Superior, with some
shoreline locations seeing up to 30 mph gusts out of the NW, though
the gusts will not penetrate too far inland with HREF mean gusts in
the interior around 20 mph at most.

Monday will be a dry day as 1019mb surface high pressure (12Z GEFS
clusters) will reside overhead. Monday and Tuesday morning both have
the potential (~20%) for morning patchy radiation fog. MOS guidance
suggests lows in the upper to mid 30s in the interior west both
mornings, which could lead to some patchy frost for elevated flat
surfaces and typical cold spots. Will hold off on any products as
the temperatures look borderline and there`s some disagreement
between the NBM deterministic and its own ensemble 50th percentile
that leads to decreased confidence. If the percentiles are to be
believed, there is around a 25% chance of some sub-freezing lows
around the Houghton/Baraga/Iron County triple point on Monday
morning and across more interior locations on Tuesday.

As the pair of troughs coalesces on Tuesday morning, the resulting
surface low around 1010mb looks to pass through Indiana/southern
Lower Michigan on Tuesday. PoPs have all but trended completely out
of the UP now, though there is still ~15% chances for the farthest
south and east portions of the UP to just get brushed by the
precipitation shield of this system. Ridging behind the system will
bring mainly clear skies and a slight warming trend of highs from
around the mid 60s on Monday to the mid 70s by the weekend. The
pattern gets a bit unclear by the weekend as the global
deterministic models struggle to resolve whether a rex block
sets up or if there is interference from a potential tropical
system in the late week, but the CPC still has the UP in a up to
50% contour of lower than normal precipitation through the end
of September regardless of exact solution.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 145 PM EDT Sat Sep 21 2024

VFR conditions should prevail at all sites through this evening,
before conditions lower to MVFR clouds late tonight in the wake
of cold frontal passage. Rain showers will also be moving in
along the front starting at IWD first this afternoon, then
reaching CMX and SAW this evening. Also, cannot rule out some
embedded thunder with the rain with the best chances of thunder
at IWD and SAW, although CMX could even see an isolated storm.
Winds will shift N-NW behind the cold front later tonight and
become gusty, gusting near 25 Kts at CMX Sunday morning.

&&

.MARINE...
Issued at 404 PM EDT Sat Sep 21 2024

Winds will remain at 20 knots or below this afternoon and early
evening. As a cold front sweeps across Lake Superior tonight, winds
behind the front will gust to near 25 knots out of the west and
northwest, first over the western portions of the lake around
midnight and then over the east around 8 AM Sunday morning. Winds
fall below 20 knots in the west through Sunday morning with winds
relaxing in the east throughout the overnight period into Monday
morning. Winds then look to remain below 20 knots as major low
pressure systems remain far from Lake Superior. As the cold front
passes tonight and Sunday, there is a chance (~30%) of
thunderstorms, though severe weather is not expected. Waves behind
the front will peak between 4 and 5 feet along the Keweenaw
Peninsula shores Sunday morning and over the east half of the lake
between 6 and 7 feet during the day Sunday, falling below 4 feet
lakewide by Monday morning.

&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
None.
Lake Michigan...
None.

&&

$$

SHORT TERM...Voss
LONG TERM...GS
AVIATION...Voss
MARINE...GS