Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 110041

Area Forecast Discussion
National Weather Service Marquette MI
841 PM EDT Thu Aug 10 2017

.SHORT TERM...(This evening through Friday)
Issued at 228 PM EDT THU AUG 10 2017

Afternoon satellite and radar loops show a broad upper-level trough
across the Upper Great Lakes region with showers and thunderstorms
developing ahead of the surface low, currently situated in far
southwest Upper Michigan, across the warm sector as a PV anomaly
begins to provide additional lift. Fairly expansive cloud cover has
lingered across the warm sector, hindering our heating a bit this
afternoon. However, fairly humid conditions were observed across the
warm sector with dew points in the low to mid 60s.

The main concern this afternoon and evening is for the potential for
strong to possibly severe storms across the south central portions
of Upper Michigan. As the surface low and upper-level PV anomaly
track eastward across northern Wisconsin and central portions of
Upper Michigan this afternoon, expect showers and thunderstorms to
increase in coverage. The better surface-based instability, with
around 1500 J/kg, is progged to nose into south central portions of
the area. Shear wise, with the mid and upper-level jet pushing east
across southern Wisconsin, the better deep-layer shear will be
displayed well south of the area. At best, we may see a brief window
where we see 20 to 25 knots of effective bulk shear this afternoon
across the south central. However, with the main upper-level wave
moving overhead, there should be enough lift to take advantage of
the instability and marginal shear for a storm or two to become
strong to severe. In fact, while the magnitude of effective shear is
not impressive, the direction shear is rather impressive. Therefore,
if a storm or two can rotate this afternoon/evening, with quasi-
steep mid-level lapse rates and dry-mid level air in place, large
hail and damaging winds look possible. Elsewhere, with MUCAPES
around 500 J/kg cannot rule out the possibility of a few rumbles of
thunder this afternoon.

Tonight through Friday, as the main system exits the area wrap
around rain showers will diminish from west to east. Still cannot
rule out a few rumbles of thunder across the central and east during
the overnight hours, but any stronger thunderstorm activity should
weaken. A few models are a bit robust compared to others in clearing
things out on the back side of the system; which seems fairly
reasonable as there is no expansive deck of stratus behind the
system across northern Minnesota at the moment. Therefore, expect
skies to gradually clear across the west during the late morning to
early afternoon hours on Friday. Across the central and east, where
onshore, upslope northerly flow is expected to persist, the clouds
may remain socked in for a good portion of the day, with drizzle at
least during the morning hours.

.LONG TERM...(Friday night through Thursday)
Issued at 349 PM EDT THU AUG 10 2017

Fairly quiet weather expected through much of the extended forecast.
There will be some afternoon showers and thunderstorms possible
Monday afternoon and more widesrpead rainfall expected toward the
end of the extended forecast.

Saturday and Sunday: The main upper-level trough axis will shift to
the east of the Upper Peninsula this weekend as dry surface high
pressure builds into the area. This will keep conditions mainly dry
for the U.P. There will probably be some afternoon fair weather
cumulus clouds that develop during the afternoon hours; however,
these will quickly diminish as the sun sets. High temperatures will
remain mainly in the 70s as at least some troughing lingers over the

Monday through Wednesday: As the upper-level trough continues to
push slowly to the east, a weak shortwave is progged to brush
through the Upper Great Lakes region Monday afternoon. At this
point, it looks like the wave will slide through during peak heating
and just enough moisture and instability will be in place to allow
for some afternoon showers and thunderstorms to develop. The best
chances will be along any lake breezes that develop during the
afternoon as these will act as the trigger/low level forcing for
development. Otherwise, the rest of this period will remain fairly
dry with a warming trend expected as upper level ridging moves into
the Upper Great Lakes. Temperatures will be in the mid to upper 70s
Monday before slowly warming to the upper 70s and low 80s by
Wednesday afternoon.

The rest of the extended: Model differences remain, on the
placement/development of a surface low progged to develop over the
Northern Plains late Wednesday night into Thursday. The GFS is much
more progressive with the upper-level troughing and development of a
surface low, while the EC keeps the ridge in place a bit longer.
This will allow for some unsettled weather toward the end of the
extended (Thursday into Friday). At this point, will stick with a
consensus of the models for this time period, introducing more of a
widespread potential for scattered rain showers.

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 834 PM EDT THU AUG 10 2017

Low cigs into the LIFR/VLIFR category have moved into IWD and CMX
with moist nrly upslope flow developing behind a low pressure system.
These lower ceilings and visibilities will eventually arrive to KSAW
later tonight, and may linger into a portion of the day on Friday.
Conditions on Friday should improve into at least the MVFR category
at KIWD/KCMX early with VFR conditions by afternoon as high
pressure and drier air builds into the region.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 228 PM EDT THU AUG 10 2017

As surface low pressure moves across Upper Michigan this afternoon
and into the overnight hours, a few observations had noted gale
force winds behind the surface low across the far southwestern
portions of the lake. These winds should subside through the
afternoon hours; however as the low pressure system does continue to
move east tonight, expect winds of 20 to 30 knots across the west
and central portions of the lake. As the system exits the region and
the pressure gradient weakens through the day Friday, winds will be
around 15 to 20 knots. Fog looks possible across the lake,
especially where area of heavy rain occur tonight into Friday.
Friday night through the middle of next week, winds look like they
will remain at or below 15 knots.

Upper Michigan...
Lake Superior...
Lake Michigan...


SHORT TERM...Ritzman
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