-- Discussion containing changed information from previous version are highlighted. --
371
FXUS63 KMQT 250511
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
111 AM EDT Sat May 25 2024

.KEY MESSAGES...

- Showers, with some thunder, return early this evening and
  shift east overnight followed by clearing skies late.

- Approaching low pressure system brings isolated shower or
  thunderstorm chances to the far west Saturday evening then
  widespread rain chances late Sunday into early Monday.
  Rainfall amounts over 1 inch are possible by Monday evening.

- Below normal temperatures and a drying trend for much of next
  week. Patchy frost possible Thursday morning.

&&

.SHORT TERM /THROUGH SATURDAY NIGHT/...
Issued at 247 PM EDT Fri May 24 2024

Water vapor imagery and afternoon RAP analyses show a negatively
tilting midlevel trough over the Northern Plains, and an associated
994mb surface low centered over the western MN border. A pronounced
dry slot is curling into central MN. Robust warm air advection and
isentropic ascent into the Great Lakes out ahead of the system has
touched off convection across WI, but so far, though high cloud
cover is overspreading the Upper Peninsula, bands of showers/storms
haven`t survived the trek through northern WI given a very dry
airmass (see early afternoon NUCAPS profiles, latest model
soundings, and surface dewpoint depressions on the order of 20
degrees). Weak radar returns moving over the UP so far are not
producing much by any way of accumulations, but have allowed for some
isolated shower activity in the forecast across the western half of
the UP the rest of the afternoon. Some rumbles of thunder will also
be possible over the far west with a few flashes over Superior
already.

Meanwhile, in spite of increasing cloud cover, temperatures have
been able to rise quite nicely across the area with most of the UP
climbing well into the 60s already. Many spots should peak in the
lower 70s today. The exception remains areas along hte lakeshores,
where onshore flow is keeping temperatures from climbing out of the
50s along Superior, and suppressing them into the lower 60s along
Lake Michigan. Winds are turning gusty, particularly across the far
western UP so far where SE gusts up to 20-30mph are becoming more
common. Winds should pick up across the central and possibly eastern
UP into the early evening with a tightening pressure gradient and
increasing winds aloft.

As the increasingly vertically stacked system off to our northwest
moves northward over the Ontario/Manitoba border region, the base of
the midlevel trough swings through the area, eventually dragging a
cold front through the area late tonight. An associated swath of
convection currently over central and southern WI reaches the
southern UP by the early evening, and sweeps through from west to
east overnight before exiting eastward during the pre-dawn hours. So
far, under a capped atmosphere, CAPE remains quite limited, and this
should not improve much heading into the evening hours. Still, a
couple hundred j/kg of elevated CAPE is present off the soundings
this evening, so will not totally rule out some thunder. As far as
rain totals go, guidance continues to favor a widespread 0.20-
0.50in, and some higher embedded totals near (and perhaps in excess)
of 0.75in mainly along the WI border. Rain ends from west to east
the second half of the night as the dry slot moves in, with clearing
skies.

Otherwise, look for breezy conditions to continue into the night,
with SE winds continuing to gust to around 20 mph ahead of the
approaching boundary. Winds turn calmer behind this while shifting
more to the WSW. Temperatures, meanwhile, fall back into the lower
40s in the western UP (behind the boundary) and in the upper 40s to
lower 50s in the east (ahead of the boundary).

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
Issued at 459 PM EDT Fri May 24 2024

The primary feature of interest for the long-term period is an
unseasonably strong low pressure lifting northeast across the region
Sunday and Monday. The UP stays on the chilly side of this system
leading to widespread soaking rain with embedded thunderstorms
possible, but nothing severe. A chilly Canadian ridge builds Tuesday-
Wednesday, lingers on Thursday, then shifts east Friday-Saturday. In
addition to being very dry with some fire wx potential, this air
mass appears cool enough to raise frost/freeze concerns. Frost seems
mostly likely/widespread Thursday morning, but may develop across
the west Wednesday morning.

Beginning with Saturday morning, rain showers should exit the far
eastern area early in the day leading to an almost completely dry
day. Mostly sunny skies allow temps to warm to around 70F amidst
breezy west-southwest winds that should limit lake breeze activity
to the eastern UP. A 30-40 knot southwesterly low level jet noses
into the western CWA around sunset with more than half of HREF
members initiating shower and thunderstorm activity across our
western tier of counties. The convective environment is CAPE
deficient with HREF means only rising to around 250 J/kg, but the
ensemble maximum approaches 1000 J/kg. The most likely outcome is
any storms that form should be limited to beneficial rain, but gusty
winds and small hail are possible if CAPE ends up being more
favorable. Probably broad-brushed PoPs too much for this time frame
since it may only occur far west, but wanted to increase from
previous forecast and kept QPF light. There is potential for QPF
>0.25" with the strongest or most persistent activity.

Sunday starts off dry with a surface low over eastern KS that
quickly moves northeast to southern WI by 00z Monday. Slowed PoPs a
bit on Sunday to account for the typical progressive bias in
NBM guidance. Also focused Sunday`s PoPs across the western UP
in the vicinity of an axis of frontogenesis extending north from
the surface low. The primary area of rainfall arrives Sunday
evening and EFI guidance shows the best signal for heavy
rainfall (>1 inch in 24 hours) across the eastern UP. Meager
CAPE combined with impressive dynamics results in chances for
embedded thunderstorms, but the primary associated hazard is to
increase rainfall rates. Dew points well above lake water temps
combined with rain and strongly convergent synoptic flow are all
favorable for a potentially dense advection fog event.

Steady rain chances shift east of the UP on Monday as showery
chances arrive across the west. These shower chances are forced by a
decaying upper level disturbance that digs southeast across the UP
Monday night and Tuesday. It`s too early to dig into the details,
but fairly chilly mid-levels suggests steep lapse rates and
diurnally enhanced rain shower chances. Precipitation amounts appear
light and should end Wednesday morning -if not sooner- as a cool and
dry Canadian surface ridge builds southeast into the area. This
ridge appears to park itself over the Great Lakes region for several
days resulting in a stretch of prime springtime weather with highs
in the 50s/60s and lows in 30s/40s beneath mostly sunny skies. There
is a threat for frost with this chilly air mass so folks with
sensitive vegetation should monitor forecasts accordingly.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
-- Changed Discussion --
Issued at 111 AM EDT Sat May 25 2024

Occluded front is currently moving across Upper MI, and shra will
end with its passage. With front already passed IWD, expect VFR to
prevail at that terminal thru the fcst period. Gusty winds to around
20kt will occur overnight and to around 25kt today. Shra and
potentially some tsra will develop this evening over western Lake
Superior. IWD may be affected, but confidence is low attm. At CMX,
front will pass in the next hr or two, bringing a wind shift from
easterly to gusty westerly to 25-30kt. LLWS will also end with
fropa. MVFR cigs may linger to mid morning under the upslope
westerly winds at CMX, but VFR will prevail thereafter. CMX has a
better chc of being affected by shra and possible tsra this evening.
Included shra mention, but no thunder given the lower confidence of
thunder impacting the terminal. At SAW, with the shra that have
occurred, upslope sse wind should result in IFR cigs setting in over
the next hr or so. Improvement to VFR will occur within 2 hrs after
fropa. VFR will then continue thru the end of the fcst period.
Westerly winds will be gusty to around 20kt at SAW today.
-- End Changed Discussion --

&&

.MARINE...
Issued at 459 PM EDT Fri May 24 2024

Northeast gales to 40 knots continue across the far western lake
with east winds of 20 to 30 knots across most of the central lake
this afternoon ahead of a low pressure currently near Grand Forks,
ND. East winds up to 30 knots gradually shift to the north-central
lake tonight ahead of a cold front that shift southwesterly.
Southwest winds around 25 knots are expected across the west half of
Lake Superior on Saturday morning before decreasing to 20 knots or
less by the evening and continuing through the rest of the weekend
as a high pressure ridge builds over the area. Another system tracks
northeast across the Great Lakes region Sunday night and Monday with
generally northerly winds of 20 to 25 knots, mainly across the
eastern half of the lake.

&&

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

&&

$$

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