Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 160525

Area Forecast Discussion
National Weather Service Marquette MI
125 AM EDT Sat Sep 16 2017

.SHORT TERM...(This evening through Saturday)
Issued at 403 PM EDT FRI SEP 15 2017

Another day with the stalled front and trough across the area. Main
impacts are thunderstorms, with an outside chance of a stronger
storm, far west over the next 2-3 hours, moderate swim risk through
this evening for Schoolcraft County, high swim risk for Schoolcraft
County Sat, dense fog potential across the Keweenaw tonight, and
possibly some strong to severe storms over the W on Sat.

Thunderstorms have formed over NW WI, far W U.P. and far W Lake
Superior as a weak shortwave lifts through. CAPE values up to 1,000
J/kg over the west with weak shear may result in a stronger storm or
two, but think chances of that are small. HRRR and RAP are also
showing some precip breaking out over the NCentral as the shortwave
passes, which is possible given the lake breeze there as an
additional focusing mechanism. Have slight chance PoPs over the

Ahead of an upper wave and the SFC low riding up the front, precip
may skirt the western U.P. Sat, with greater chances for precip as
the wave/low approaches later in the day. Some of the storms could
be strong to severe given potential for up to 2,000 J/kg of cape and
effective shear values of 20-30kts. Large hail and damaging winds
the primary threat.

Dense fog is possibly over the Keweenaw tonight with E winds off the
Lake. Not confident enough to issue any headlines though.

With large waves along the beaches of Schoolcraft County, the mod
swim risk will continue into this evening, with larger waves and a
high swim risk on Sat. The night shift will issue the headline if

.LONG TERM...(Saturday night through Friday)
Issued at 348 PM EDT FRI SEP 15 2017

Guidance continues to hold onto the dominant upper level ridge
across the eastern CONUS through the weekend; however, there
continues to be some nudging to the east which could bring the
upstream trough further east towards the Upper Peninsula. Will
continue to bring steady increases of precip and possibly thunder.
With a low pressure system lifting north of the forecast area Sun,
guidance indicates a frontal boundary will precede a surface ridge
of high pressure late in the weekend into early next week. This will
then allow dry weather to return.

The pattern does start to become more active with a quasi-zonal
orientation from Tue-Thur of next week. This will bring periodic
chances for showers and possibly thunder, but also with more
seasonal temps.

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 125 AM EDT SAT SEP 16 2017

LLWS at all sites overnight and at KSAW Saturday evening. Expect
showers to generally hold off to the west through much of the

At KCMX, LIFR to VLIFR conditions in CIGS and fog are expected
into early overnight with eastern flow off the lake and plenty of
upstream low level moisture. Conditions should improve by early
Saturday morning to VFR as winds shift to a downslope southeast

At KSAW, a narrow band of showers will impact the terminal early
this morning, otherwise moist southeast upslope flow could lead to
some patchy fog/stratus overnight but uncertainty is such that kept
VFR conditions thru the period.

At KIWD, moist northeast flow off Lake Superior will lead to LIFR
stratus clouds into early overnight but once winds shift southeast
early Saturday morning expect improvement to VFR.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 403 PM EDT FRI SEP 15 2017

An inverted surface trough currently anchored across Lake Superior
will begin to weaken tonight. NE winds to 20 to 30 knots may
occasionally gust to 35 knots into early tonight before weakening.
Winds will then increase on Sunday out of the W gusting to 20-30
knots. Otherwise, winds will be below 25 knots..

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


LONG TERM...Beachler
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