506
FXUS63 KMQT 271917
AFDMQT

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

.KEY MESSAGES...

-Rounds of showers Friday into Saturday and 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 WEDNESDAY/...
Issued at 359 AM 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
pressure over the Red River Valley (of the north), 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 50-70% hourly PoPs Friday morning while the
cold front is still between Minneapolis and Fargo. Showers 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, 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.

By Saturday, the cold front will be approaching the UP, providing
better forcing, though the 00Z GEFS still suggests only around 10%
of members with SBCAPE values above 500 J/kg, so the thunderstorms
that do form will struggle to become strong. GEFS mean daily QPF on
Saturday ranges from around an inch in the Keweenaw to around a half
inch in Menominee, which both are well short of flash flooding
guidance and will most likely not be enough to impact river
flooding.

PoPs fall off behind the front, with precipitation expected to be
ended by 12Z Sunday morning. This is supported by a ~1025mb high
pressure that will be over southern Minnesota by Sunday afternoon
and over the Michigan 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.

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. The GEFS shows 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 as
the CPC outlooks that the first half of July is still more
likely to be warmer and wetter than normal.

&&

.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 359 AM 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 west half of
the lake Friday into Friday night. As winds veer westerly behind the
front on Saturday, wind gusts across the lake will be 20-25 kt. 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, increasing the wind gusts to around and above 20
kt into 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 4-6 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...GS
AVIATION...Rolfson
MARINE...GS