Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 101800

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

.SHORT TERM...(Today and tonight)
Issued at 447 AM EDT THU AUG 10 2017

The SFC low currently over the MN/WI border will shift E across the
southern U.P. today. Widespread precip currently across the CWA
should clear out over the central Upper Peninsula, especially over
the south-central. Clearing may allow for instability to increase to
1,500-2,000 J/kg over the south-central and along the WI border,
with the magnitude and coverage dependent on that clearing. Do
think there is a large hail and strong wind threat over the south-
central and along the WI border given the instability, which is
backed up by SPC SREF Calibrated Severe Thunderstorm Probabilities
around 15-20 percent, but that threat will be pulsy due to
limited shear around 20 kts.

Precip will then become more focused near Lake Superior and the
eastern U.P. tonight.

.LONG TERM...(Friday through Wednesday)
Issued at 233 AM EDT THU AUG 10 2017

Nam shows a 500 mb low over Lake Superior 12z Fri that slowly moves
east this forecast period and the upper Great Lakes remains in an
upper level trough through 12z Sun. Deeper moisture and weak 850-500
mb q-vector convergence move out of the east half of the U.P. on Fri
night. Looks dry then for Sat and Sat night. Did not make too many
changes to the going forecast.

In the extended, GFS and ECMWF show a 500 mb trough over the upper
Great Lakes region 12z Sun which remains through Tue. At the sfc,
high pressure remains over the area into Wed. Shortwave ridging
moves into the area at 500 mb on Wed and then is replaced with
another shortwave trough for Thu. Temperatures look to stay near
normal for this forecast period. Highest chance for rain will be Thu.

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 120 PM EDT THU AUG 10 2017

Challenging aviation forecast today as low pressure currently
situated near KIWD this afternoon pushes east across Upper Michigan
this afternoon into the overnight hours. Ahead of this low, showers
and thunderstorms are expected at KSAW this afternoon, with
lingering showers and perhaps some lingering drizzle early Friday
morning. Behind the low at KIWD/KCMX ceilings and visibilities will
deteriorate down into the IFR category through the late afternoon
and tonight as cooler air moves over the area and upslope flow
develops from the northwest. These lower ceilings and visibilities
will eventually arrive to KSAW later tonight, and may linger into a
good portion of the day on Friday. Conditions on Friday should
improve into at least the MVFR category at KIWD/KCMX through the
late morning hours.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 200 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. Friday night through the middle of
next week, winds look like they will remain at or below 15 knots.

Upper Michigan...
Lake Superior...
  Gale Warning until 5 PM EDT /4 PM CDT/ this afternoon for LSZ162.

Lake Michigan...


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