266
FXUS63 KMQT 010721
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
321 AM EDT Mon Jul 1 2024

.KEY MESSAGES...

- There is a slight chance (<20%) for patchy frost across
  portions of the interior-western UP early this morning.

- Dry weather continues through this evening.

- Next rounds of showers and thunderstorms arrive Monday night,
  continuing into Wednesday. Gusty southerly winds up to 25-35
  mph are also expected on Tuesday.

- Low chance (~25%) of afternoon and low to medium chance
  (25-40%) of evening showers/storms across the western half
  of Upper Michigan on July 4th. Rain spreads over the region
  Thursday night and Friday.

&&

.UPDATE...
Issued at 922 PM EDT Sun Jun 30 2024

Main fcst concern overnight is how low temps will fall, and with
that, the potential of frost for the first morning of July. Sfc high
pres will be settling over the western Great Lakes during the night,
allowing for calm/near calm conditions tonight across the fcst area.
Skies are already clear, and the air mass is very dry. Precipitable
water tonight will be running just 30-40 percent of normal to
enhance what is already setting up to be a good radiational cooling
night. Afternoon dwpts bottomed out in the mid 30s F at some sites
across the fcst area, and that is likely a good indicator of where
temps will be heading at the traditional interior cold spots. 12z
MET guidance for KLNL had a min temp of 34F tonight, also a good
indicator of where traditional interior cold spots across the w will
end up. Fcst has been updated to knock a few degrees off of min
temps. While fcst reflects mid/upper 30s F across a fairly large
portion of the interior, would not be surprised at all to see the
typical cold RAWS sites fall toward 30F. Expected coverage of
possible frost across the interior w is still very low and spotty
given the isolated nature of the lowest temps that are supportive of
frost and also the short duration of the those lowest temps.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 231 PM EDT Sun Jun 30 2024

Robust upper ridging over the Plains is supporting a sprawling
1028mb surface high centered over MN this afternoon. With strong
subsidence over the UP, there is hardly a cloud in the sky. In spite
of this, temperatures remain quite cool; temperatures are only
climbing into the lower 60s across much of the UP, while shoreline
locations and the easternmost portions of our CWA are struggling
even to break out of the upper 50s under chilly NW flow off of Lake
Superior. NW winds are staying somewhat gusty across the eastern
half of the UP, but gusts should fall back heading into the
evening.

Tonight, as the aforementioned high pressure becomes centered
overhead, even stronger radiational cooling and calm winds will lead
to widespread overnight lows in the upper 30s to lower 40s. The
frost potential across the interior-western UP is still difficult to
pin down, with most of the guidance staying just warm enough to
preclude frost. Only about 10% of href ensemble members reach the
mid 30s, while the NBM 10th percentile also only flirts with the mid
30s. Will note, however, that some spots in the western half of the
UP fell farther into the 30s than expected, with the "winner" of the
night (Watton) reaching as low as 34F. Therefore, have been just
confident enough to come in a couple degrees under guidance,
particularly across Iron and southern Baraga counties, where we
may just get cool enough for patchy frost. This will continue
to be monitored/adjusted as needed.

In addition, dangerous swimming conditions for Marquette and Alger
counties are expected through this afternoon.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
Issued at 320 AM EDT Mon Jul 1 2024

Primary focus in the extended forecast period continues to be the
broad mid-upper level trough shifting out of the northern Rockies
beginning tonight. This system will amplify and support a surface
low developing this afternoon over eastern Montana/western Dakotas.
As the main trough axis/closed low aloft shifts east into Manitoba
tonight, the surface low will lift to near Lake Winnipeg, and then
to northeastern Manitoba/far northwestern Ontario by Tuesday
afternoon. Its expected to continue lifting north Tuesday night.
This progression will result in two waves of precip lifting through
our forecast area, in addition to a strong low level jet and
tightening pressure gradient resulting in gusty winds.

The first wave of precip is expected to slide east late tonight and
Tuesday as a surface trough rotates through. Models continue to
highlight an environment lacking much in the way of instability, but
the elevated MUCAPE of ~200j/kg means a thunderstorm can`t be ruled
out. A lull is expected by afternoon in the west, which will shift
east through the evening as the initial swath of precip exits into
Ontario. As this initial wave moves through, a strengthening
pressure gradient over the region will ensue as a strong 925-850mb
40-50kt low level jet presses overhead. Even with modest dinural
mixing, gusty southerly winds will develop, particularly near the
Bay of Green Bay, Lake Michigan, and the downslope and higher
terrain locations in the Gogebic Range, Michigamme Highlands, and
lakeshore areas of Marquette and Alger counties. NBM appears certain
of 25-30 mph wind gusts in these locations and eastern Upper
Michigan and suggests ~25% chance of exceeding 35 mph. Model
soundings that suggest effective mixing suggest potential upwards of
40 mph. The second wave will lift northeast into the U.P. Tuesday
night ahead of the eastward migrating cold front. Between guidance
available last night and tonight, there appears to be a better
handle on when precip should end, with most now ending precip in the
east Wednesday morning.

A surface ridge extending northwest should help support a mostly dry
day on Wednesday, although there is a brief period in the east that
could destabilize enough for afternoon showers/storms to develop
before the cold front clears. The 4th of July should start off dry
thanks to the lingering effects of the surface ridge and a meso high
developing over Lake Superior. Upstream though, another trough exits
the northern Rockies and presses through the Plains. Guidance
amplifies the shortwave and lifts a surface low through the eastern
Dakotas and into Minnesota in the afternoon/evening. There`s good
agreement among the guidance packages that this wave will shift east
through Minnesota and Wisconsin through the day Friday, then lift
northeast through Upper Michigan Friday night into early Saturday.
Best chances for precip with this wave will be Thursday night and
Friday. Its unclear if it will remain dry Thursday afternoon and
evening in the western half of Upper Michigan. While probability is
currently low (~25%), Thursday afternoon destabilization could result
in convection developing. Additionally, increasing isentropic ascent
may support showers lifting into the region during the evening hours
(25-40%). Anyone with evening firework plans across the western half
of Upper Michigan should continue monitoring the forecasts.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 125 AM EDT Mon Jul 1 2024

Very dry air mass associated with high pres settling over the Great
Lakes overnight thru today will result in VFR continuing thru this
fcst period at IWD/CMX/SAW. Winds will be light to calm at all
terminals overnight, then during today, southerly increasing to
around 10kt, except becoming ESE at CMX. LLWS is likely to develop
at all terminals near the end of or just beyond this fcst period.

&&

.MARINE...
Issued at 320 AM EDT Mon Jul 1 2024

Light winds will persist over Lake Superior today with high pressure
continuing to influence the region.

A system will begin lifting from the Plains into Canada tonight,
then continue lifting northward Tuesday into Wednesday. The passage
of this system will result in at least 2 rounds of rain and storms
and two periods of stronger winds. Expecting the first round of
showers, maybe with a thunderstorm embedded within to shift through
Lake Superior late tonight and Tuesday. These showers may support
fog developing and periods of low visibility on the lake. As the
system approaches tonight, tightening pressure gradient will develop
while a strong 40-50kt 925-850mb low level jet moves over eastern
Lake Superior. There`s still a great deal of uncertainty in how much
of these stronger winds will mix to down to the surface given the
increasing stability of the over lake environment. However, recent
internal probabilistic tools are beginning to highlight nearshore
areas downwind of the Michigan lakeshores and the stretch from
Marquette northward into Canadian waters as those most likely to
experience low end gales. This tool is only suggesting a 20-40%
chance, which is in the middle of the road of probabilities when
comparing to the HREF and the NBM. These ~40% values may also be
somewhat representative downwind of the lakeshores east of Marquette
and along the northern shores of the Keweenaw, where models struggle
with the land/lake interface and localized terrain driven influences
have been known to mix down stronger winds to the surface. At this
point, given the uncertainty and the isolated nature of the stronger
mixing downwind of the lakeshores, will hold off on a gale watch and
allow the next shift to reexamine it again.

Another round of moisture will lift through Tuesday night into
Wednesday while the effects of the low level jet wane. The cold
front presses through west to east Tuesday night into Wednesday
morning, allowing winds to become westerly/southwesterly for
Wednesday. Another period of stronger winds up to 20-30kts, looks
possible between the Keweenaw and Isle Royale Wednesday in this
southwesterly flow. High pressure returns briefly for Thursday with
a weaker low pressure system expected to pass over the Upper Great
Lakes late Friday and Saturday. Light winds below 20 kts returns
Wednesday night, continuing likely into the weekend.

&&

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

&&

$$

UPDATE...
SHORT TERM...LC
LONG TERM...JTP
AVIATION...Rolfson
MARINE...JTP