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500
FXUS63 KMQT 252324
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
724 PM EDT Sat May 25 2024

.KEY MESSAGES...

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- Showers and embedded thunderstorms develop across MN/WI this afternoon
  and track northeast across the western UP this evening.

- Approaching low pressure system brings widespread rain late
  Sunday into early Monday. Rainfall amounts >1 inch are
  possible by Monday evening.

- Below normal temperatures for the first half of the week,
  followed by a drying trend midweek. Patchy frost possible
  Thursday morning.
-- End Changed Discussion --

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 348 PM EDT Sat May 25 2024

It`s been a profoundly pleasant spring day with temps around 70F, a
westerly breeze, and mostly sunny away from the lakeshores. There
has been some lake breeze activity across the eastern UP, but
synoptic winds prevented boundaries from pushing inland. The
Keweenaw has been breezy with the Houghton Airport reporting a few
WSW gusts to 45 mph, but values in the 25-35 mph range were more
common across the peninsula. Satellite imagery shows a healthy
diurnal cumulus field across the western UP that extends upstream
across MN/WI in the vicinity of a nearly stationary frontal
boundary. Cloud base observations are in the 6-8 kft range
indicating a deeply mixed boundary layer that may take some time to
saturate.

Looking ahead through tonight, a nearly vertically stacked low
pressure east of Lake Winnipeg gradually weakens while barely moving
tonight. Meanwhile, an unseasonably strong low pressure deepens to
around 995 mb over eastern KS this evening. A subtle shortwave and
associated vorticity maxima tracks northeast along the
aforementioned frontal boundary. This disturbance is likely to
trigger a small area of showers and thunderstorms across the western
UP this evening. The nose of a ~45 kt southwesterly low level jet
provides additional forcing for rain showers. There are mixed
signals for thunder chances with this activity due to small CAPE and
moderate synoptic/mesoscale forcing. The latest 19z SPC mesoanalysis
analyzed >250 J/kg SBCAPE with values >500 J/kg across south-central
MN. Satellite imagery shows an area of agitated cumulus
collocated with an expanding area radar returns WNW of
Minneapolis. This lines up very well with HREF guidance
initiating activity in this location, with coverage expected to
expand northeast along the front late this afternoon. This
activity is expected to be knocking on our western doorstep
around 00z/8 PM eastern before tracking northeast across the
Keweenaw. There is uncertainty with how far southeast this
activity tracks, but current forecast keeps most QPF west of
Iron/Marquette Counties and that seems reasonable to me.

&&

.LONG TERM /SUNDAY THROUGH SATURDAY/...
Issued at 342 PM EDT Sat May 25 2024

Active pattern for Upper Michigan continues in this forecasting
period. The long term pattern for Upper Michigan will start off with
an anomalous surface low and shortwave lifting northeast into the
Great Lakes Sunday and Monday. From there, broad mid-level troughing
establishes itself across the eastern half of North America before
ridging gradually builds into the region for the latter half of the
week and into the weekend. Together, these will yield early week
rain with cooler temperatures, followed by a dry period midweek and
warming temperatures late week.


After early morning rain showers pull out of the western UP, expect
one more brief period of dry weather through the morning ahead of an
approaching shortwave and deepening surface low ejecting out of the
Plains. This tracks somewhere between northern IL and southern WI by
Sunday evening, and will continue to move ENE into the Lower
Peninsula Sunday night through Monday before moving north of Lake
Huron and rapidly deepening by Monday evening. PWATS building to 1-
1.5 across the region coupled with increasingly strong dynamics
should yield widespread rain for Upper Michigan by Sunday afternoon,
persisting until the system pulls away Monday. QPF varies per model
given persistent subtle differences in track, but the general
thinking is widespread 0.5-1.5 inches of rain, with those most
likely to see the higher amounts being the central and eastern
portions of Upper Michigan. Precip should end west to east through
the day Monday, but another shortwave pressing eastward across
Minnesota/Wisconsin, followed by a more broad shortwave dropping
southeast out of Ontario/Manitoba Monday night may support shower
activity into Tuesday night. The best potential for additional
rainfall during this period will be across the eastern UP, closer in
proximity to the deep low to our northeast and the wraparound
moisture being directed into the area. High pressure and a dry
airmass builds into the region Wednesday and should maintain mostly
dry conditions for the forecast area to finish at least through
early Friday.

As the early week surface low pulls away, a cool airmass will rotate
into the region. Daytime temperatures on Tuesday/Wednesday look to
be in the 50s and 60s with overnight lows in the 40s and 30s. That
said, NBM 25th percentile shows temperatures dipping below 35F
across much of the interior UP by Thursday morning; with light winds
and a cool and very dry airmass, temperatures flirting with frost
advisory criteria are a good bet. Dewpoints, too, will be something
to watch during the midweek period. Dry and well-mixed soundings,
particularly Wednesday, could lead to plummeting dewpoints and RH
falling into the lower 30s%. A mitigating factor for the fire
weather risk, in addition to fairly light winds, will be the
widespread rain in the preceding days.

Ridge axis builds into the region Thursday night while another
trough presses out of the Rockies. Current thinking is for surface
high to maintain its spot over the region until the eastward
progressing trough shifts into the region. This could allow PoPs to
creep into the western UP as early as Friday.

&&

.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
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Issued at 723 PM EDT Sat May 25 2024

Shra and isold tsra are currently developing from nw WI into nw
Upper MI. These shra/tsra will affect IWD/CMX this evening for about
a 2-3hr period. While VFR should continue, can`t rule out brief MVFR
if any of the heavier shra pass over the terminals. Overnight, sw-ne
oriented frontal boundary across western Lake Superior may continue
to support shra, possibly affecting CMX, so VCSH was included for a
good part of the night at that terminal. Low pres lifting toward the
western Great Lakes on Sun will bring renewed shra development in
the aftn at IWD/CMX. Not expecting conditions to drop out of VFR
thru this fcst period, but deteriorating conditions are likely Sun
evening. At SAW, VFR will prevail. Shra may approach SAW near the
end of this fcst period with deteriorating conditions to follow
during Sun night.
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&&

.MARINE...
Issued at 342 PM EDT Sat May 25 2024

Low pressure over the Ontario/Manitoba border continues to track
northward this afternoon while weakening. Winds remain elevated
across western Lake Superior, coming in out of the SW and continuing
to gust to around 20-25kts through the early evening while to the
east, SE winds are coming in at around 10 knots. Winds across the
western half of the lake fall below 20 knots later this evening.  A
slight chance of thunderstorms exists on and off throughout tonight
in the southern part of western Lake Superior, including the
Keweenaw, and lingering mid-lake into Sunday morning.

By early Sunday morning, weak high pressure building into the region
results in light southerly flow of less than 5-15 kt, backing to the
E/SE by mid-morning ahead of an approaching low over the Plains.
Waves fall to around 1-3ft. By early Sunday evening, winds are
forecasted to be easterly across Lake Superior at 10-15 kt. Winds
continue to back and build throughout Sunday night as the Colorado
low approaches, reaching northerly by Monday morning at 15-20 kt and
waves building to 3-5 ft. A slight chance of thunderstorms exists on
eastern Lake Superior very early Monday morning.

Backing continues until Monday night, when steady northwesterly flow
becomes established at 10-20 kt, being higher potentially up to
25kts in eastern Lake Superior. This northwesterly flow and wave
heights of 3-5 ft are expected to remain steady until Wednesday
midday when high pressure begins to build into the area. At this
time, expect light and variable winds and decreasing waves until
Thursday midday, when light southerly flow at 5-15 kt re-establishes
itself, along with waves 1-3 ft, for the remainder of the forecast
period.

&&

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

&&

$$

SHORT TERM...EK
LONG TERM...LC
AVIATION...Rolfson
MARINE...LC