868
FXUS63 KMQT 272004
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
404 PM EDT Thu Jun 27 2024

.KEY MESSAGES...


-Rounds of showers are expected Friday into Saturday and then Monday
night into Tuesday with quiet weather following each round.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 316 PM EDT Thu Jun 27 2024

It`s a pleasant late June aftn across Upper MI under sfc high pres
centered over the western Great lakes. Temps generally range from 60-
65 along the Great Lakes to the lwr 70s F inland. Dwpts are
comfortably low, ranging from around 40 to around 50F. Cu has
developed away from stabilizing flow off of the Lakes, and a streak
of high clouds is spreading over western Upper MI. Off to the w,
water vapor imagery and RAP analysis show a well-defined shortwave
trof over the nw U.S. This feature will bring the next round of
shra/some tsra to Upper MI during Fri into Sat. Ahead of that trof,
a weaker shortwave across the Plains is generating shra and a few
tsra from ND across sw MN into western IA.

Clouds will be on the increase from w to e tonight. Shra associated
with the lead Plains wave should reach western Upper MI in the 09z-
12z time frame. Prior to that, a modest increase in 850mb theta-e
and increasing 850mb flow may support a few isold -shra across
western Upper MI after 06z. Will be warmer night tonight than last
night under increasing clouds and stirring winds. Expect min temps
ranging from around 50 e to 55-60F w.

&&

.LONG TERM /FRIDAY THROUGH THURSDAY/...
Issued at 403 PM EDT Thu Jun 27 2024

It will be an active end to the work week and beginning of the
weekend as an approaching trough and associated surface low pressure
feature pass directly over the UP Friday and Saturday. These will
force showers and thunderstorms, of which an isolated storm on
Friday may be strong to severe. Despite the prolonged period of
shower chances, flooding rainfall is not expected. High pressure
then sweeps over the Great Lakes Sunday and Monday, allowing for
some nice summer weather. The next round of precipitation looks to
be late Monday into Tuesday, but the surface low associated with
those showers looks to not be particularly strong and also displaced
well to the north, so impacts should be relatively low. Model spread
increases beyond then, but a continued warm and wet pattern is
expected to continue.

Beginning Friday, a 500mb trough will be over eastern Montana and
quickly progressing east. This will support an upper-990s mb low
developing over the Northern Plains, causing a strengthening
southerly surface flow setup. 850mb warm advection, isentropic
upglide, and 500mb PVA will all contribute lift for showers well
ahead of the main surface front, with the HREF suggesting widespread
60-90% hourly PoPs spreading into the western UP Friday morning
while the cold front is still between Minneapolis and Fargo. Will
note that rainfall rates continue to be maximized over Lake Superior
and the far western UP, closer in proximity to the warm front and
left-exit region of the LLJ that may be providing a little extra
lift.

Convection in the morning should be fairly weak as instability is
meager, but HREF mean MUCAPE suggests by 00Z Wednesday, instability
in the IWD vicinity will be approaching 500 J/kg, so some afternoon
thunder is within the realm of possibility. It is definitely a low-
CAPE, high-shear environment, with HREF mean 0-3km SRH values well
north of 200 m2/s2. Reflectivity paintball plots indicate strong
convection firing upstream along/ahead of the cold front, so
depending on if those storms can survive as they progress eastward,
an isolated severe storm cannot be ruled out over the west, but
there is plenty of uncertainty given the lack of instability.
Meanwhile, PWATs up to 2in indicate a potential for some decent
rainfall amounts, with most of the guidance showing a widespread
quarter to half-inch of rain area-wide and some heavier amounts
potentially approaching an inch in the heaviest of downpours. This
would be most likely across the western UP ahead of the cold front.
As this is well below even hourly flash flood guidance,

Shower activity continues into the first half of Friday night ahead
of the cold front, then tapers off as a dry slots works in. Then,
another shortwave dropping through with an associated (albeit
weaker) cold front will touch off additional chances for showers
during the afternoon hours Saturday. With soundings indicating a few
hundred j/kg of CAPE, particularly across the south-central UP where
we may be able to see some partially clearing skies early in the day
Saturday, some thunder is not out of hte question. Otherwise, given
a rather moisture-starved column, any rain totals should be light,
generally a tenth of an inch or less.

PoPs fall off behind the front, with dry weather expected as early
as 06Z Sunday. This is supported by a ~1025mb high pressure that
will be over southern Minnesota by Sunday afternoon and over the
Lower Peninsula by Monday afternoon. This will lead to a couple of
nice sunny days, though Sunday will definitely be the cooler day of
the two as cool northerly flow aloft will keep highs mainly in the
60s Sunday, but winds becoming southerly Monday will allow highs to
rebound to seasonal 70s. Dewpoints could be worth watching Sunday as
soundings show a good potential for these to mix out (even reaching
values in the 30s!) but light winds and plenty of recent rainfall
continue to temper our fire risk.

Precipitation chances begin to ramp up Monday night into Tuesday as
the next trough exits the Rockies and a surface low passes generally
through northern Ontario. Ensembles show this low as only marginally
stronger than 1000 mb and as even the southernmost cluster of lows
remains well north of the UP, dynamics should be fairly weak over
the UP, so hazardous weather seems unlikely at this time. Following
the passage of showers, another dry period is expected Wednesday,
but to what extent that dry weather lasts is uncertain as ensemble
spread increases significantly, though a pattern change is still not
expected with CPC outlooks continuing to favor wet weather through
early July.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 143 PM EDT Thu Jun 27 2024

VFR will continue at all terminals thru this evening under a
lingering dry air mass associated with high pres. Later tonight and
Fri, a low pres trof approaching from the w will bring lowering
clouds and eventually shra. Although a few stray shra could arrive
over western Upper MI late tonight, the main area of shra should
reach IWD around 12z and CMX around 14z. Conditions will quickly
fall to MVFR at both terminals once shra begin. LLWS will develop at
IWD/CMX late tonight/early Fri morning as well. At SAW, VFR will
prevail thru this fcst period as shra hold off until some point
during Fri aftn.

&&

.MARINE...
Issued at 403 PM EDT Thu Jun 27 2024

Under high pressure, wind gusts will remain below 20 kt through
today and tonight. As a cold front approaches from the west,
southerly wind gusts increase to 20-25 kt across the western half of
the lake by Friday afternoon, then across the eastern half by Friday
evening. Wind gusts fall below 20kts Friday night while veering
westerly, but then a secondary front dropping through will bring
another round of 20-25kt gusts across much of the lake for the
daytime hours Saturday. The return of high pressure will keep wind
gusts below 20 kt Saturday night through Monday night before the
next system passes through northern Ontario, causing southerly winds
to increase to around and above 20kts for Tuesday.

Long-duration southerlies on Friday will cause waves over the
northern portions of the lake to increase to 4-6 ft. The westerlies
behind the cold front passage will cause 3-5 ft waves over the
eastern half of the lake Saturday night. Thunderstorms will also
threaten the lake Friday and Saturday, with some strong to severe
storms possible over the western portion of the lake Friday evening.

&&

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

&&

$$

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