973
FXUS63 KMQT 200729
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
329 AM EDT Sat Jul 20 2024

.KEY MESSAGES...

- 30-60% chance of showers and thunderstorms mainly over the
southern half of the UP this afternoon/evening. Severe weather not
expected.

- Next chance of showers/storms Tuesday/Wednesday.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 328 AM EDT Sat Jul 20 2024

Morning water vapor and RAP analyses reveal an anomalously deep
cutoff low moving into northern Quebec, remnants of an MCV spinning
over the eastern Dakotas/western MN, and an elongated vort max
moving east of Lake Superior. Ridging extends from the Desert
Southwest into the Canadian Rockies. This is supporting surface high
pressure over the Canadian Prairies, which is expanding
east/southeast into Ontario in the wake of the exiting low.
Altogether, this is pushing a weak surface cold front southward
towards Lake Superior early this morning, indicated by some cooler
cloud tops on satellite and weak radar returns over the far northern
portions of the lake.

The cold front continues to drop southward over the lake through the
early morning hours, and may finally touch off some shower activity
across the northern UP after sunrise. However, given the timing of
the frontal passage (that is, before peak heating and
destabilization), convection across the northern half of the UP
should be spotty at best. Showers and storms look to increase in
coverage as the front heads towards the WI border into the early
afternoon, with simulated reflectivity favoring the south-central UP
(spanning from Iron through Delta  counties) for more numerous
showers/storms. Per the HREF and model soundings, SBCAPE should
increases to around 500-1000j/kg by then, though shear remains low
and midlevel lapse rates unimpressive. Thus, strong convection is
not expected. Still, with a narrow corridor of PWATS in the
neighborhood of 1.5in and rather slowly-moving storms amid lighter
wind fields, some heavier downpours would not be out of the
question. Ensembles favor around a widespread 0.10-0.25in of rain,
but some higher embedded amounts around and in excess of 0.50in are
possible (50% chance among the hi-res ensemble members). Showers
drop south of the UP closer to sunset.

Otherwise, expect temperatures starting in the mid 50s-lower 60s
this morning to climb into the lower to mid 70s by mid-morning in
the northern half of the UP. Behind the front, temperatures should
hold steady the rest of the day or even fall back slightly
(especially closer to Superior); the southern half of the UP should
be able to see highs ranging in the upper 70s to lower 80s before
the front finally drops through later in the day.

Into tonight, clearing skies, light winds, and a cooler airmass
should yield lows several degrees cooler than early this morning.
Expect lows in the lower to mid 50s across most of the area, while
some portions of the interior-western UP potentially see
temperatures dipping into the 40s.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
Issued at 247 PM EDT Fri Jul 19 2024

Low-level frontal boundary discussed in the short term section will
continue progressing south through the UP on Saturday while losing
upper level support as the parent low continues shifting eastward
into Quebec. This may result in a few showers in the northern half
during the morning and early afternoon, but should be no more than a
nuisance if anything. Relatively more widespread coverage of showers
and thunderstorms expected over the southern half (highest near the
WI/MI border counties) where the arrival of the front will coincide
with a modestly destabilizing diurnal boundary layer. SBCAPE progged
by the HREF mean mainly in the 500-1000 J/kg range, but
midlevel lapse rates are weak and winds through the column are
very light, so any storms should be of the garden variety. There
could be a few heavier downpours with likely slow moving storms
and a narrow ribbon of 1.5-1.75" PWATs, but overall low impacts
expected. Saturday night into Sunday, big bubble no trouble as
the Ontario high continues to expand over Lake Superior and the
UP. Highs both days fairly seasonable, a little cooler near the
big lake due to onshore flow.

Another tranquil day Monday under the influence of the high, but
weak warm advection should boost temps a couple degrees to the
seasonably warm side. Western NOAM ridging remains strong into next
week, while shortwave energy dives south along its eastern flank.
Deterministic guidance is showing some of this energy consolidating
and possibly cutting off in the vicinity of the upper Great Lakes.
This will bring our next chance at showers and thunderstorms in the
Tuesday/Wednesday frame, along with cooling temps by Wednesday.
Temps look to rebound with a drying trend for the end of next week
as this low moves out. In fact, some summer warmth could return
Friday into next weekend as there are indications that some of the
western US ridging folds eastward into the upper Great Lakes.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 115 AM EDT Sat Jul 20 2024

VFR conditions will continue through the TAF period. The only
forecast concerns are a northerly wind shift with an approaching
cold front set to cross the UP in the daytime hours (12-18z) and
some incoming cloud cover, though, not expecting any drop to MVFR or
lower. Some spotty showers are possible along the boundary, however,
more convective activity is possible in the southwest UP
(potentially at IWD) along the MI/WI border as the cold front
interacts with max diurnal destabilization. Confidence in shower or
afternoon thunderstorm coverage is low, but I did include a VCSH at
SAW Sat afternoon where shower coverage will probably be the best of
all the TAF sites.

&&

.MARINE...
Issued at 517 PM EDT Fri Jul 19 2024

Southwest winds up to 20 knots over mainly the west half of Lake
Superior will diminish below 20 knots tonight as a cold front
moves through overnight into early Saturday. There is a slight
(20%) chance for storms developing along this boundary to make
it across the lake later tonight, but confidence is low. Winds
stay light, mainly below 20 kts at least through Monday. Winds
increase out of the NE across the western portions of the lake
Tuesday with another shortwave trough moving through. Gusts
around 20kts are possible. This is also our next decent window
for showers/storms to move over the lake (20- 30% chance) before
mainly dry weather returns midweek onward.

&&

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

&&

$$

SHORT TERM...LC
LONG TERM...Thompson
AVIATION...Voss
MARINE...Voss