094
FXUS63 KMQT 050742
AFDMQT

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

.KEY MESSAGES...

- Showers today. A 40-60% chance of some areas across the south
  receiving in excess of an inch of rainfall.

- Mainly dry Saturday, but a rain shower cannot be entirely
  ruled out 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.

&&

.SHORT TERM /THROUGH THIS AFTERNOON/...
Issued at 341 AM EDT Fri Jul 5 2024

Water vapor imagery and RAP analysis show a well-defined
shortwave/mid-level low over eastern MN/western WI. Ahead of the mid-
level dry slot lifting around e side of the circulation, a band of
shra extends from ne WI wnw into MN, aided by isentropic ascent,
especially over ne WI. These shra have spread across the MI/WI
stateline recently with new development also occurring in s central
Upper MI ahead of the main band of shra. Current temps range thru
the 50s with some lwr 60s F s central.

Mid-level low will drift e today with deep layer forcing per q-
vectors strongest during the morning thru early to mid-aftn. With
more persistent isentropic ascent focused into the central and
eastern fcst area, expect the more persistent/heavier pcpn over that
area, but especially s central/se where isentropic ascent is
generally best focused this morning. The nw fcst area, Keweenaw in
particular, may not see any shra today. Beyond mid-aftn, forcing
weakens, and models all show a corresponding decrease in
coverage/intensity of pcpn at that time. Precipitable water is
running about 130-140pct of normal with the pcpn today, so not
unusually high to support excessive rainfall. However, given the
persistence of the shra, local amounts of an inch or two are
possible. 00z HREF has the probability of exceeding 1 inch at 40-
60pct, but exceeding 2 inches at no more than around 20pct. At least
to this point, KMQT radar has only showed some of the shra having
small cores with instantaneous rainfall rate estimates of 1-3
inches/hr. There is some instability noted for non sfc-based
parcels, and with mid-level dry slot advecting toward the area,
can`t rule out some rumbles of thunder today across the southern
fcst area. So far, GOES GLM has only detected a few lightning
flashes either side of the MI/WI stateline. Clouds/shra will hold
temps down today with highs ranging thru the 60s F. Will be coolest
across the central, especially n central, due to ne winds off of the
lake.

&&

.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.

&&

$$

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