526
FXUS63 KMQT 042304
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
704 PM EDT Sat May 4 2024

.KEY MESSAGES...

-Rain overspreading the UP from west to east this
 afternoon/evening as a low pressure system moves through the
 area.
-Dry conditions expected Sun/Mon, though mostly low winds and
 antecedent rainfall should broadly limit fire concerns.
-Complex pattern setup for the midweek as multiple low pressure
 systems interact in the Midwest. Precipitation chances highest
 on Tuesday, but PoPs linger through the end of the week.
 Thunder potential highest Tuesday and Wednesday.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 312 PM EDT Sat May 4 2024

A shortwave trough moving through the Northern and Central Plains as
noted on water vapor imagery will be propelling a cold front across
Upper Mi this afternoon and evening, spreading showers from west to
east across the fcst area. The leading edge of showers is into
southern Houghton and western Iron counties as noted on the latest
radar imagery as will continue to move through central Upper Mi from
20-00z and then into the eastern U.P. counties 00-03Z before exiting
the eastern cwa by 09Z. Elevated cape of a few hundred j/kg and steep
mid-level lapse rates could support a rumble of thunder into south
central and eastern zones late this afternoon into the evening hours.

Ridging and subsidence behind the shortwave and associated cold
front will support drier conditions behind the front tonight and
maybe some partial clearing over portions of the western U.P. later
tonight. The moist low levels from the showers along with the
prospect of partial clearing however could also support the
development of stratus/patchy fog behind the front. Min temps tonight
will generally range from the upper 30s west to the lower 40s
central and east.

&&

.LONG TERM /SUNDAY THROUGH SATURDAY/...
Issued at 346 PM EDT Sat May 4 2024

Sunday, 500mb heights begin to rise as ridging builds over the Upper
Midwest, contrasted with troughs over Hudson Bay and the western
CONUS. The ridge over the midwest will support a 1020mb high
pressure settling over the Upper Great Lakes through late Monday.
This will give the UP as a whole its driest stretch of the last few
weeks with high confidence of no precip through at least early
Tuesday morning. The main forecast concern will be how dry the
airmass gets for Sunday and Monday, as efficient mixing and
radiative heating under clear skies will allow RHs to fall. As the
mixed layer rises to near 7kft in the interior west Sunday
afternoon, RHs look to fall just below 30 percent. Using the NBM
10th percentile of dewpoints to calculate RHs Monday gives RHs
falling to the lower 30s. With mostly light winds below 10 mph
gusting to 15 mph expected (and CAMs even suggesting a lake breeze
off of Lake Michigan) along with prior rainfall, fire weather
concerns should be fairly low.

The trough over the west becomes a bowling ball closed 500mb low as
it emerges on the other side of the Rockies Monday, negatively
tilting as it does. Height falls over the Northern Plains cause
500mb height anomalies over Montana and North Dakota to fall to -26
dam. This will support strong lee cyclogenesis, with the 12Z GEFS
showing a near-980 mb low over the Northern Great Plains. Meanwhile,
a near-120kt 300mb jet will be on the south side of the parent
trough, with divergence aloft supporting cyclogenesis further south.
Ensemble clusters bring this secondary low pressure into the Upper
Great Lakes at roughly 990s mb, but there is considerable spread as
to the interaction of these two low pressures, the timing and
strength of each, and the implications of each variable. Ensembles
vary significantly on thunder potential, with especially the 00Z
Canadian ensemble suite having multiple members with ~1000 J/kg of
SBCAPE in the afternoons of Tuesday and Wednesday, but other members
have instability never overcoming any caps. Given the uncertainty,
did not deviate from NBM PoPs, which bring up to 90% PoPs Tuesday
afternoon for much of the UP, falling off by Wednesday morning to
near 30%. PoPs never truly fall off through the week as enough
ensemble solutions have low pressure stalling near the Great Lakes
to warrant at least 15-25% PoPs into the weekend. Peeking beyond the
next week, ensembles favor ridging over the western CONUS and
troughing over the eastern CONUS, leaving the UP in a somewhat drier
northwesterly flow pattern, reflected in each CPC precipitation
outlook to favor below normal precip through the end of May.

&&

.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 704 PM EDT Sat May 4 2024

Expect the transition to MVFR conditions across KCMX and KSAW by 00z
this evening as KIWD hangs onto LIFR conditions for at least a
couple more hours. However, with cigs being higher than previously
expected, I`m thinking there`s about a 50% chance that higher
conditions, including VFR conditions, remain across KCMX and KSAW
into late tonight, with lower chances (20 to 30%) of the better
conditions remaining into the morning hours on Sunday. However, what
gives me pause on going with the more optimistic forecast is the
recent rainfall and the propensity of our area to produce patchy fog
across the area behind rainfall. Thus, while I have improved
conditions a little quicker in comparison to the previous TAF
forecast, I have kept the lower conditions in for now; there
certainly could be some amendments for the terminals tonight though
if the good conditions continue/improve across the area.

Going back to the patchy fog, there is a chance (30 to 40%) that it
could bring conditions down to around airport mins tonight,
particularly at KCMX and to a lesser extent KIWD; this concern is
noted via the SCT cloud decks at 02z and 07z at KIWD and KCMX,
respectively. While the chance is small (10%), KSAW could see some
marginal LLWS tonight from time to time behind the cold front
tonight. VFR conditions return across the region Sunday morning, if
not sooner.

&&

.MARINE...
Issued at 346 PM EDT Sat May 4 2024

Behind showers today, high pressure settling over the Upper Great
Lakes through Monday will cause winds to remain below 20 kt. Monday
evening, developing low pressure systems over the Great Plains will
compress the pressure gradient and cause northeasterly wind gusts to
funnel near Duluth Harbor to 20-25 kt. As low pressure approaches
Lake Superior Tuesday and into the midweek, wind gusts up to 30 kt
are forecast. There is gale potential if the low pressure tends to
be on the stronger side of guidance and the low tracks directly over
Lake Superior, but probabilities are currently only around 20% for
widespread, frequent gusts over the gale force threshold.
Uncertainty in the forecast increases greatly into the later
portions of the week, though winds are currently expected to be
around 20 kt in the wake of the low pressure.

&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
  Small Craft Advisory from 5 AM to 2 PM EDT Sunday for LSZ250-
     251.

Lake Michigan...
None.

&&

$$

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