315
FXUS63 KMQT 220845
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
445 AM EDT Sat Jun 22 2024

.KEY MESSAGES...

- Wet pattern continues into early Sunday with some periods of
  patchy fog.

- The heaviest rainfall should stay south of the UP, but there
  is still a slight chance (15% chance) for locally heavy rain
  resulting in minor flooding impacts across south central and
  southeast portions of Upper Michigan.

- Another round of showers/thunderstorms is possible Sunday and
  Monday night into Tuesday.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 444 AM EDT Sat Jun 22 2024

     More showers to move in today and tonight with the
heaviest/steadiest rainfall central and east...

Latest water vapor imagery and current RAP analysis currently show
broad mid-level ridging over the Upper Great Lakes early this
morning but this will give way to a couple of upstream shortwave
troughs of interest, one over southern/central MN and another over
western SD. The initial shortwave trough over MN is expected to move
across the Upper Great Lakes today with the second trough from the
Dakotas expected to move across the area tonight. Both these
shortwaves along with an associated sfc low pressure system will
support periods of rainfall across the U.P. today into tonight.
Based upon the tracks of the shortwaves and the associated sfc low
along with the most favorable fcst forcing from mid-level fgen and
isentropic ascent would expect the heaviest and most prolonged
rainfall to occur over south central and east half portions of the
U.P. today through tonight. Weak elevated instability could support
isolated t-storms as well, mainly south central and southeast.
Currently, only isolated to scattered light rain showers are
occurring over south central UP but expect this coverage to increase
to numerous or widespread toward sunrise as it spreads slightly
farther north and east in response to the shortwave trough moving in
from MN. It is worth noting that WPC does have the southeast half of
the U.P. (roughly along and east of a line from Iron Mountain to
Harvey) in a slight risk for excessive rainfall today into tonight
as PWATs range from 1.5 to 2 inches across much of the area or
nearly 200% of normal. Would expect the most vulnerable areas for
risk of flash flooding would be urban or poor drainage areas
southeast if training of stronger showers/storms occurs over these
areas. With the expected moist conditions will also continue to
carry a mention of patchy fog in the grids through much of the
period.

Under mostly cloudy skies, temps today will generally be in the
lower to mid 60s, although could be in the upper 50s along the Lake
Superior shore. Lows tonight will be mostly in the 50s.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
Issued at 304 PM EDT Fri Jun 21 2024

Deterministic and ensemble guidance packages continue to highlight
the potential for multiple rounds of showers and thunderstorms in
the extended forecast period as Upper Michigan sits primarily under
near-zonal to northwest flow aloft. During this period, daytime
temperatures will start off cool, but trend back into the 70s and
80s for the first half of the work week.

Beginning Saturday, surface low will lift northeast along a warm
front into the Great Lakes as a shortwave presses east through
Minnesota. This will support a deepening surface low Saturday
afternoon into early Sunday as the low transits Wisconsin and lower
Michigan. Precip along and north of the boundary will build into the
region through the day as PWATS remain 1.75-2 inches. Recent NBM and
LREF guidance suggests a high (>75%) chance of exceeding 1 inch of
rain across the southern half of the forecast area, with 30-60
percent chance across the north half. While most deterministic
guidance suggests a widespread 0.5-2 inches through Sunday morning,
GEFS and EC ensemble means suggesting the same supports the higher
confidence in a potential notable and widespread rainfall event.
This generally matches the EC EFI and SOT, which paints much of the
south half with 0.8-0.9 EFI and 2 for SOT, indicating a potential
extreme rainfall event outside of climatology. It should be noted
though, that even if widespread 1-2 inches of rain does occur,
recent RFC flash flood guidance suggests 2+ inches of rain in 1-6
hours would be needed to raise flash flooding concerns. Given that
this is not the case with this event, flash flooding is not a
concern. With that being said though, given recent rainfall, I`d
expect some ponding of water in low lying locations and some
additional river rises through the next few days if we do experience
this rainfall. Additionally, rainfall amounts will be dependent on
where the low tracks and where the warm frontal boundary stalls
across Wisconsin, which a general clustering analysis of the EC and
GEFS ensembles still suggests a range of locations. Model soundings
suggest a mostly capped atmosphere across the area, with some
elevated instability noted across the south. With this in mind, some
embedded thunderstorms can`t be completely ruled out, but strong or
severe thunderstorms aren`t expected at the moment. Daytime highs
Saturday should be in the 60s to near 70F while overnight lows dip
into the 50s to upper 40s across the forecast area.

Precip should end Sunday morning from west to east as the low pulls
away and weak mid-level ridging transits the area. This break
appears to be short-lived though, given the clipper-like shortwave
pressing southeast across Ontario/Lake Superior in the
afternoon/evening. The GFS and NAM suggest the morning rain should
end early enough to enable small daytime destabilization through the
day, which would support thunderstorms to accompany the
afternoon/evening wave. At the moment, strong or severe weather
aren`t anticipated.

High pressure over the area Monday should keep the region dry while
upstream, a ridge rolling impulse moves east through the
Dakotas/Minnesota and a surface low tries to develop. By Monday
night, precip chances increase for Upper Michigan as a cold front
extending south of a low moving through Manitoba and the low moving
through southern Minnesota press closer. These swing into the Great
Lakes on Tuesday. Ahead of the front, daytime temps could warm into
the 80s across much of the region Tuesday. High pressure and dry
conditions builds in Wednesday into Thursday. Beyond this, guidance
differs greatly on the timing and position of the next wave.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 140 AM EDT Sat Jun 22 2024

Next round of showers will move in overnight and will bring
deteriorating conditions with them. IWD will be VFR overnight
and then IFR Saturday with LLWS coming in late Sat afternoon
into the evening. CMX will be VFR and then by late Saturday
afternoon, rain moves in there with LLWS and MVFR conditions
setting in by evening. SAW will be VFR until around 12Z Saturday
morning when rain moves in and then drops to MVFR. By late Sat
afternoon, heavier rain and IFR/LIFR conditions move in. LLWS
sets up at SAW by Sat evening.

&&

.MARINE...
Issued at 304 PM EDT Fri Jun 21 2024

A deepening low pressure system will gradually lift into the region
tonight and Saturday, before exiting into Ontario Sunday morning. As
this transit occurs, expect winds to shift to northeasterly/easterly
across Lake Superior tonight before becoming northerly Saturday
night and northwesterly by Sunday morning. Light winds of 20kts or
lower are mostly expected in this event, although northeast winds
going down into the Duluth Harbor Saturday may climb to near 25 kts
at times. Additionally, as winds shift to the north Saturday night,
expecting an increasing to 25-30 knots across central and eastern
Lake Superior as the peak pressure gradient force shifts through.
Winds lighten to 20kts or less Sunday and predominately remain there
until at least Tuesday. At this point, expecting southerly winds to
increase to near 25 kts ahead of a transiting cold front.

Thunderstorms will be possible, mainly Sunday afternoon/evening and
then again on Tuesday. Winds may be erratic near these, but at the
moment, strong or severe thunderstorms are not expected.

&&

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

&&

$$

SHORT TERM...Voss
LONG TERM...JTP
AVIATION...07
MARINE...JTP