879
FXUS63 KMQT 051924
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
324 PM EDT Wed Jun 5 2024

.KEY MESSAGES...

- Some high-base showers and thunderstorms look to develop over
  the western half of the U.P. this evening. A strong
  thunderstorm or two with gusty winds and hail is possible.
- Showery weather and much cooler conditions expected Thursday
  through the weekend under the influence of low pressure.

&&

.SHORT TERM /THROUGH THURSDAY NIGHT/...
Issued at 323 PM EDT Wed Jun 5 2024

GOES-16 Visible imagery shows clearing skies along the MI/WI state
line behind an advancing cold front, with the band of rain showers
from that front now mainly confined to the eastern half of the UP.
Through 1830Z, the only electrically active storm has been a sub-
severe cell that started in southern Menominee County and has
transited the Bay of Green Bay and is imminently arriving at the
Garden Peninsula. Under cloudy skies for much of the day, highs are
around 10 degrees cooler than yesterday, mainly in the low 70s.

Attention turns upstream this evening to the clearing in the
west, which already is showing signs of some cu development
supported by diurnal heating and a secondary shortwave evident
on RAP Analysis 500mb heights. The 12Z HREF showed much less
available instability relative to yesterday`s storms with only
around 500-1000 J/kg of SBCAPE available. Shear is right around
what it was yesterday with around 20 kt of effective bulk shear
and 50-100 0-3km SRH. It is worth noting that while instability
is surface-based, the depth of the mixed layer at the surface is
around 6,000 ft, so cloud bases are going to be relatively
high. Reflectivity paintball plots in the HREF show that CI will
begin in northern Wisconsin and push east into the UP around
20Z, somewhat losing energy as it progresses and maintaining
cellular form. Thinking hazards are once again isolated damaging
wind gusts and pea to quarter sized hail from "core dumps".
Less total precipitation is expected with this round of showers,
with HREF mean 6-hourly precipitation only around 0.2-0.4
inches. In the wake of showers, lows look to fall to the 50s
tonight, with winds staying out of the west.

&&

.LONG TERM /TONIGHT THROUGH TUESDAY/...
Issued at 515 AM EDT Wed Jun 5 2024

Flow over and around N America thru early next week will feature
pronounced high latitude blockiness. Through the remainder of this
week and into the weekend, building mid-level ridging/positive
height anomalies, first from ne thru n central Canada and across the
Arctic Ocean, and then over western N America will force troffing to
develop from s central Canada across the Great Lakes/eastern U.S.
The last 24hrs of medium range model guidance has trended toward the
western ridge deamplifying/progressing downstream a little quicker
next week, resulting in quicker weakening/eastward progression of
the troffing affecting the Great Lakes. For Upper MI, this pattern
evolution will lead to a period of blo normal temps (seasonably
cool) thru early next week. However, the large scale pattern does
suggest the potential of unseasonably cool days in the mix,
particularly on Thu. The aforementioned model trends for next week
suggest a little more aggressive warming that would bring temps back
to around normal early in the week and then above normal late week.
Farther down the road, the end of the ensemble guidance and the 00z
June 4 ECMWF weeklies suggest we`re probably heading toward an
overall warm last half of June as heights build across the central
and eastern U.S. The CFSv2 counters that idea to some degree with
coolness lingering a little longer thru mid month. As for pcpn over
the next 7 days, the development of the mid-level troffing from s
central Canada thru the Great Lakes region will support showery
weather at times Thu thru the weekend. Models have lacked run-to-run
consistency and have been and continue to be quite varied on the
details of the flow affecting Upper MI. So, pcpn fcst has much more
uncertainty than normal. Overall, expect many areas to be dry much
of the time as shra are likely to be sct in coverage on most days.
Thu is likely to be the day with the most nmrs shra. With mid-level
trof weakening and drifting e early next week, dry weather is more
likely to prevail.

Beginning tonight, secondary cold front will sweep across the area
in association with another shortwave quickly following today`s
wave. Shra/tsra arriving over the w late aftn will continue eastward
thru the evening with the risk of strong/gusty winds diminishing
with loss of daytime heating and stabilization. Overnight,
broadening mid-level low centered nw of Lake Superior will increase
its influence over Upper MI. Within the circulation, another
shortwave will approach from northern MN. As a result, some shra
will linger thru the night.

On Thu, Upper MI will be situated firmly under mid-level low
circulation with center over or very near to Upper MI. Shortwave
tracking se from ne MN combined with the start of daytime heating
will support a rapid development/expansion of shra during the
morning. The shra should diminish in coverage over the w in the aftn
in the wake of the wave. Considerable cloud cover will limit daytime
heating/instability, so thunder potential is overall minimal. Fcst
will only include a mention of thunder over the e and se fcst area
due to a little more instability potential before clouding over and
development of widespread shra. Under considerable cloudiness,
passing shra, rather stiff wnw winds and 850mb thermal trof driving
se into the area, it will be unseasonably cool for much of the area.
Highs in the 50s F will likely be the rule across the w thru n
central ranging up to the low/mid 60s F s central/se. Lakeside
locations exposed to wnw winds across Lake Superior may not see max
temps above 50F. W side of the Keweenaw likely to be coolest.
Showers will diminish Thu night in the wake of shortwave, but won`t
end, particularly over the e where there is actually some isentropic
ascent as warmer air to the n and ne weakly advects toward the
thermal troffing over the area.

On Fri, center of mid-level low drifts e toward southern Ontario.
Weak shortwave ridging develops into western Upper MI btwn that low
and another mid-level low over s central Canada. This is suggestive
of fewer shra over western Upper MI on Fri compared to Thu, more
areas likely to be dry thru the day. To the e, closer to the mid-
level low, there will be a greater chc of shra. High temps on Fri
will be coolest over the e where more clouds/shra are expected. Mid
50s to around 60F expected there. Low/mid 60s expected to the w,
except closer to Lake Superior where temps will be in the 50s.

Over the weekend, the lack of run-to-run consistency and model
disagreement on the details of the flow from s central Canada thru
the Great Lakes region leads to decreasing confidence in pcpn
chc/coverage, and that plays a role in temps as well. As a result,
fcst is generally broad brushed with 30-50pct chc of shra, targeting
the aftn hrs when a little instability will aid shra development.
Expect high temps in the 50s near Lake Superior in areas exposed to
nw winds across the lake and 60s F inland.

With medium range models trending toward troffing easing and
shifting e early next week, expect a trend to dry weather across the
board. For the moment, there`s not really any support for including
a specific shra chc Mon or Tue. There`s some indication of a
shortwave trof to affect the Upper Lakes on Wed, and that would
offer the next mention of chc shra. Temps will head back to around
normal.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 134 PM EDT Wed Jun 5 2024

VFR prevails at all TAF sites to begin this afternoon. -SHRA has
moved out of IWD and CMX with SAW forecast to also clear out of
precip in the next hour or two. This evening, a second wave of
showers is expected to move in from the west, with some stronger
TSRA possible at IWD. VFR is expected to prevail through these
SHRA/TSRA. In the morning hours, low (20-40%) SHRA chances return to
the forecast along with likely (50+%) reductions in ceiling height
to MVFR, though models have trended later with the onset of MVFR
conditions over the last few model cycles. Expect winds to remain
primarily out of the west, occasionally gusty.

&&

.MARINE...
Issued at 515 AM EDT Wed Jun 5 2024

Low pres trof currently over western Lake Superior will continue
eastward, exiting the eastern lake mid to late aftn. While wind
gusts to around 20kt are expected today, showers and thunderstorms
along/ahead of the trof may result in locally enhanced winds just
ahead of and just behind the trof. A secondary trof will lead to
more thunderstorms developing over MN and moving out across western
Lake Superior this aftn/evening, posing a risk of locally strong
wind gusts. During tonight and Thu, steady w to wnw winds generally
at around 20kt with occasional gusts to 30kt will set in from w to
e. These winds will remain unchanged thru Fri. A slight diminishing
of winds will occur over the weekend with sustained speeds falling
back to around 15kt.

Also of note, there will likely be some fog present thru this
evening, mainly across the e half of Lake Superior. Passage of
second trof should clear the fog off of the lake during tonight.

&&

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

&&

$$

SHORT TERM...GS
LONG TERM...Rolfson
AVIATION...GS
MARINE...Rolfson