053
FXUS63 KMQT 050512
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
112 AM EDT Fri Jul 5 2024

.KEY MESSAGES...

-Good chance (~60%) of some areas getting an inch of rain
 Friday, though flooding rainfall is not currently forecast.

-Mainly dry Saturday, but a rain shower cannot be entirely ruled
 out (20-30%) along the MI/WI state line in the afternoon.

-Sunday through Wednesday, daily chances of showers and
 thunderstorms, highest chances in the afternoons.

-Dry period begins Thursday, could be dry into next weekend.

&&

.UPDATE...
Issued at 832 PM EDT Thu Jul 4 2024

Quick update to expand low PoPs eastward to roughly western
Alger/Delta and points west except for the Keweenaw. Nothing
impactful with just a few light showers falling from high cloud
bases associated with a weak leading wave, but perhaps enough to
cause a minor annoyance for those out and about this evening. Main
slug of rain associated with trailing stronger wave arrives later,
likely approaching the MI/WI border around 06/07Z (1-2 am CDT).

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 326 PM EDT Thu Jul 4 2024

This afternoon, weak high pressure ridging remains over Upper
Michigan ahead of another shortwave that is analyzed over the
Dakotas. A couple waves of convection associated with this are
moving through MN and into northern WI, and cirrus continues to
stream into the UP from this upstream convection. Meanwhile, closer
to home, the Superior lake breeze is quite apparent on radar,
already heading well inland into the UP. So far, just agitated cu
with this sporadically apparent on satellite beneath the cirrus
deck, but weak radar returns are finally popping on the Lake Michigan
boundary in the eastern UP. Will not rule out spotty shower activity
(and perhaps some rumbles of thunder) along the lake boundaries,
mainly across the central and eastern UP. Heading into the late
afternoon and evening, spotty showers and storms currently across
northern WI may be able to make it into the southern UP, but better
chances for rain hold off until later tonight (more on that later).
By then, with several hundred j/kg of CAPE, some thunder will be
possible. Any thunderstorm could put down some gusty winds and a
brief heavy downpour.

Otherwise, winds remain on the lighter side, but may shift suddenly
with the passing lake boundaries. Temperatures inland have been able
to climb well into the 70s and even around 80F, but where onshore
flow is having an impact, temperatures are hovering in the lower to
mid 70s, even falling back into the 60s.

Overnight, the shortwave moves over MN and into WI with a surface
low closing off over central WI. Expect showers (with some thunder)
to increase in coverage after midnight, mainly across the western UP
as the surface low continues its eastward trek. There is a chance
for some decent rainfall amounts at times in the resulting
deformation zone; href ensembles note a potential (20-30% chance)
for rainfall rates rainfall rates of a quarter-inch per hour in the
heaviest downpours overnight. So, while not a washout, we could
expect a widespread quarter to half-inch of rain over the western
half of the UP, with some isolated spots seeing even higher amounts
closer to an inch. Temperatures, meanwhile, stay fairly mild
overnight with lows generally in the mid 50s.

&&

.LONG TERM /FRIDAY THROUGH THURSDAY/...
Issued at 352 PM EDT Thu Jul 4 2024

After a very progressive pattern kicked off this summer, a more
blocky pattern has now emerged as 500mb ridging over western North
America will only very slowly progress eastward with time throughout
this forecast period. The consequence of this for the UP will be
dealing with the low-amplitude shortwaves that spill southeast from
the ridge, and one such shortwave will be over the UP on Friday. The
resultant surface feature is a 12Z GEFS-mean 1007mb low pressure
over Wisconsin passing south of the UP through Friday. As the UP
will be on the north side of the commahead, much of the UP is
expected to be under the precipitation shield during Friday morning.
The 12Z HREF does show precipitation becoming much more scattered in
the afternoon hours though, particularly over the central UP. As the
surface destabilizes somewhat during the afternoon hours, a few
thunderstorms are expected as HREF mean SBCAPE climbs to near 500
J/kg, but these are mostly expected to be garden variety
thunderstorms and not severe. With PWATs climbing above 1.25 inches,
some heavy downpours are expected, with the HREF showing around a
60% chance that somewhere in the west-to-central UP sees an inch of
rainfall in the morning and similar chances for the eastern UP in
the evening hours. Chances of 2+ inches, where flooding might be a
concern, is around 10-30% in the west early and in the south-central
late. Given the strongest forcing (which is not incredibly strong to
begin with) will be south of the UP and NAEFS indicates the PWATs
and IVT are around normal for this time of year, flooding rainfall
is not forecast, but it is still expected to be a wet end of the
week for the UP.

By Saturday morning, the low will be nearly completely departed from
the area and showers will dry up, with the final showers being in
the far eastern UP and upslope light rain showers in Alger County.
Weak surface ridging is expected to take the place of the departing
low, as the high pressure center is forecast to be near TN at 1015
mb. Because the high is so weak and far away from the UP, not enough
subsidence will be present to completely preclude some diurnal
showers along the MI/WI state line, but impacts should be low. A
quiet night is expected Saturday night, but cloud cover begins to
increase ahead of the next shortwave trough sliding southeast off
the western ridge. Global deterministic models do begin to diverge
here as to how this trough progresses, but the general outcome seems
to be a mainly diurnal pattern of precipitation Sunday through
Wednesday with lower PoPs in the overnight periods in between. Given
how weak synoptic surface forcing is, the ability of diurnal forcing
to help initiate showers will be key in determining PoPs as well as
thunderstorm chances, though severe weather is unlikely because of
said lack of forcing. Most deterministic guidance does have the
trough beyond the UP by Wednesday, so PoPs are lower by a fair
margin on Wednesday, but enough ensemble spread exists to keep at
least 20-30% PoPs in the forecast for now. As the ridge aloft shifts
over the Four Corners area from the Pacific Coast from where it was
centered, high pressure does look to settle over the UP for
Thursday, with the 12Z GEFS showing a ~1020mb high over the UP
Thursday morning and building to the mid 1020s mb over the rest of
the Great Lakes basin by the weekend. This will usher in a dry
period to end next week, with the potential of a multiple-day period
of no rain across the UP, something that has not been common this
summer so far.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 112 AM EDT Fri Jul 5 2024

VFR conditions in place to start the 06Z TAF cycle. A surge of
moisture and rain showers should impact at least IWD/SAW
overnight into the morning, with cigs falling to MVFR and IFR.
CMX looks to be on the edge of the rainfall so VFR was
maintained with this cycle, although confidence on placement of
precipitation is fairly low. An embedded TS cannot be ruled out
at IWD roughly 08-14Z and SAW 10-16Z, but coverage too low for
inclusion in the TAFs. Gradual improvement in cigs expected
through the day, but IFR conditions may hang on at SAW until
early afternoon.

&&

.MARINE...
Issued at 352 PM EDT Thu Jul 4 2024

As a ridge aloft over the western CONUS creates a blocking pattern,
Lake Superior will see a particular lack of strong pressure systems
passing overhead, and as a result, the slackened pressure gradient
will keep wind gusts below 20 knots and waves at 3 feet or below for
nearly the entire forecast period. That being said, there are still
a few weak disturbances that will cause chances of thunderstorms
periodically throughout the next week, mainly during the daytime and
in the nearshore zones.

&&

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

&&

$$

UPDATE...
SHORT TERM...LC
LONG TERM...GS
AVIATION...Thompson
MARINE...GS