-- Discussion containing changed information from previous version are highlighted. --
513
FXUS63 KMQT 261738
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
138 PM EDT Sun May 26 2024

.KEY MESSAGES...

- Instability showers pop up in the west this afternoon.

- 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.

&&

.SHORT TERM /THROUGH THIS AFTERNOON/...
Issued at 238 AM EDT Sun May 26 2024

Upper air pattern consists of a closed 500 mb low over western
Ontario with a shortwave over the northern plains. The shortwave
heads east into the upper Great Lakes by 00z Mon. Did introduce some
pops into the area this afternoon as a narrow ribbon of deeper
moisture and some 850-500 mb q-vector convergence sets in in the
west, but only have chance pops in there. The east continues to look
dry with dry east low level flow. Did not make too many changes to
the going forecast.

&&

.LONG TERM /TONIGHT THROUGH SATURDAY/...
Issued at 336 AM EDT Sun May 26 2024

Recent deterministic and ensemble guidance packages continue to
highlight an active pattern for Upper Michigan 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 today, then lingering Monday. From there, broad mid-
level troughing establishes itself across the eastern half of North
America while at the surface, the aforementioned surface low slows
and maintains cyclonic flow over the region through at least Tuesday
night. From there, ridging builds into the region for the latter
half of the week. Together, these will yield early week rain with
cooler temperatures, followed by a dry period midweek and warming
temperatures late week.

Starting tonight at 0z, EC and GEFS ensemble surface low clustering
continues to suggest a good bit of uncertainty for where the surface
low will be considering how far out this is, but the general
consensus is that the surface low will be over southeastern WI,
southern Lake Michigan, or Illinois. As the night progresses and the
mid-level shortwave lifts northeast, the surface low will follow,
spreading 1-1.5 inch PWATS into the forecast area as it lifts into
northern Lower and then into Ontario north of Lake Huron by Monday
afternoon. During this transit, the mid-level shortwave is expected
to amplify and take on a negative tilt, increasing the dynamic
response and enabling the surface low to deepen some. The
deterministic GFS and EC track of the low and the system`s
deformation zone line up fairly well with where their respective
ensemble`s projected higher probabilities of exceeding 1 inch of
rain in 24 hours. These guidance packages suggest these areas,
across central and eastern Upper Michigan, have a 50% or greater
chance of exceeding 1 inch during this event. Guidance suggests the
western UP is favored for less, draping a gradient of 10-50% of
exceeding half an inch across the region. Rain should end west to
east through the day on Monday.

As this low slowly pulls away, broad troughing extending across
Ontario and the Upper Great Lakes will enable continued cyclonic low
and mid level flow while a shortwave presses east across the
northern Plains into Minnesota/Wisconsin Monday afternoon and night
and yesterday`s system drifts back southward into the Midwest
Tuesday. This evolution will support continued scattered rain
chances through Tuesday night. High pressure and a dry airmass build
into the region Wednesday and should maintain mostly dry conditions
through at least early Friday.

As the early week surface low pulls away, a cool airmass will rotate
into the region. Daytime temperatures Monday through Wednesday look
to be in the 50s and 60s with overnight lows in the 40s and 30s.
Frost may be a concern for portions of the interior west Tuesday
night and for most interior locations Wednesday night. Confidence is
highest for Wednesday night given our internal model certainty tool
suggesting a 15-50% chance of falling below 35F for interior
portions of Upper Michigan and NBM probabilities for the same
suggesting a 15-30% chance. While still possible Tuesday night, the
timing of the drier air and potential for continued winds above 5
mph suggest radiating out may be more difficult. Dry and well-mixed
soundings, particularly Wednesday and Thursday, could also lead to
plummeting dewpoints and RH falling below 30% away from the
lakeshores. 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 the
surface high to maintain its spot over the region until the eastward
progressing trough shifts into the region. This enables PoPs to
creep into the western UP as early as Friday.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
-- Changed Discussion --
Issued at 138 PM EDT Sun May 26 2024

Low pressure tracking northeast across Lake Michigan tonight brings
renewed shra development into Upper MI with the highest chances at
SAW and lowest at IWD. A 35-45 knot low level jet accompanies rain
chances leading to LLWS at IWD/SAW that subsides Tuesday morning.
VFR will prevail at all terminals today before lowering to MVFR late
this evening at IWD/CMX to IFR cigs at SAW. Northerly upslope flow
at IWD/SAW is expected to lower cigs to IFR/LIFR and may also result
in fog and vsby decreasing below IFR thresholds late tonight into
Monday morning. Otherwise VFR cigs/vsby prevail until tonight with
winds gradually backing from easterly this afternoon to
northwesterly by tomorrow afternoon.
-- End Changed Discussion --

&&

.MARINE...
Issued at 336 AM EDT Sun May 26 2024

Main item of interest is a northeastward lifting surface low that`s
expected to move through Lake Michigan and northern Lower Michigan
tonight into Monday. Today, ahead of this system, expect light
southerly flow in the east and northeasterly in the west backing
east/southeast as the low approaches. Winds will continue to back
and build throughout Sunday night as the Colorado low approaches.

When looking at the GEFS and EC ensemble surface low clustering,
there`s poor agreement on where the individual members believe the
system will track. More northern solutions yield stronger winds
tonight and Monday, while more southern solutions yield weaker
winds. With more northern options being more consistent run to run,
opted to increase winds in this forecast package closer to these
solutions. Current thinking is that northeast winds will increase to
near 30kts across the east half tonight and Monday, but it should be
noted that low end gales cannot be ruled out. For example, the
latest and previous EC run suggests 34-40 knot gales in and around
Whitefish Point by Monday afternoon.

The low will slow northeast of Lake Superior Monday night, enabling
northwesterly flow through at least Tuesday. During this period,
gradient forces should gradually weaken, enabling winds to slowly
fall below 20kts by Tuesday night. High pressure builds in at that
point, which supports light and variable winds and decreasing waves
until Thursday midday, when light easterly to southeasterly flow at
5-15 kt re-establishes itself, along with waves 1-3 ft.

&&

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

&&

$$

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