Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 201737

Area Forecast Discussion
National Weather Service Marquette MI
137 PM EDT SAT AUG 20 2016

.SHORT TERM...(Today and tonight)
Issued at 646 AM EDT SAT AUG 20 2016

The 5H trough continues to dig into the northern plains this morning
per the latest satellite WV imagery. Additional energy moving into
the backside of this feature will help enhance the surface low
currently over the central Mississippi Valley, with this low
deepening as it moves into northeast WI and eastern Upper Michigan
during the day. The low will then shift northeast out of the region
overnight while high pressure builds into the central plains.

Multiple forecast challenges exist in the short term due to the
track and strength of the surface low. There will be plenty of rain
associated with this system especially across the central and east
as those areas showing 1.5-2 inches PW per latest Bufkit soundings.
And while instability is rather low, a weak vort max lifting through
the area along with the right entrance region of the 3H jet passing
by should be enough to help bring some of the thunderstorm activity
over WI into central and eastern Upper Michigan this afternoon,
especially if there is a break in the cloud cover there due to some
slight mid-level drying as shown on satellite. Winds will be quite
gusty once the low passes through the area but the main impacts will
be over the marine zones. Still, exposed areas along the Superior
lakeshore east of Marquette and along the higher terrain of the
Keweenaw may see occasional gusts up to 40 mph. temperatures for
today will also be slightly challenging as if there is a brief break
in the sky cover over the east, temperatures there could rise a
little higher than currently expected. Weak cold air advection over
the west along with plenty of sky cover to help keep lows there
below seasonal averages.

.LONG TERM...(Sunday through Friday)
Issued at 411 AM EDT SAT AUG 20 2016

Greatest weather impacts during the extended will be Sunday morning
with continued very strong and gusty winds expected over the east
half of Lake Superior and along the east half of Upper Michigan
along the Lake Superior shoreline.

Sunday: The low pressure system is progged to be over far eastern
Lake Superior by 12Z Sunday as the 500mb trough axis is positioned
over the eastern half of the U.P. Plenty of moisture will be in
place across the CWA in the morning to keep scattered rain showers
in the forecast. This will be a result of the proximity to the low,
wrap around moisture as well as 850mb temperatures dropping to
around 5C to 6C. Lake surface temperatures are around 20C, according
to buoy readings, which would create delta T values around 14-15C.
This would result in lake enhanced rain showers with the north to
northwest winds across the area. Winds will continue to be very
gusty over the eastern half of Lake Superior and over the eastern
half of the U.P. between 12Z/22-18Z/22 due to the tight pressure
gradient, mixing down of stronger winds from aloft on cool advection
and enhancement due to the isallobaric wind component. The pressure
change associated with the isallobaric component is progged to be
around 6-8mb between roughly 12Z and 15Z Sunday. The addition of all
the aforementioned wind elements will likely continue to give wind
gusts 35 to 45 mph over Lake Superior and along the eastern
shoreline of Lake Superior, with some of the models showing as high
as 50 mph wind gusts. Between 18Z and 00Z/23, the low pressure
system is progged to shift east of the U.P. allowing the pressure
gradient to relax across the area. This will allow winds to decrease
below 15 to 25 mph by mid to late Sunday afternoon. The rain showers
will also be on a diminishing trend in the afternoon as the low
continues to slide east and winds begin to shift out of the west.
While Sunday will continue to be a dreary day, there will be a high
swim risk for the beaches along Marquette and Alger county, likely
requiring a headline.

Sunday night through Tuesday: As the aforementioned low pressure
system slides into Quebec Sunday night, a surface high pressure
ridge and upper level height rises will slide into the CWA. This
will put the U.P. on the inflection point between ridging aloft and
the trough to the east. Drier air will also be in place allowing for
dry conditions for Sunday night. The surface ridge in place will
allow for light winds and clear skies. This will cause pretty good
radiational cooling for inland locations. Generally kept lows in the
low to mid 40s inland as pwats only drop down to around 75 percent
of normal Sunday night. Overall moisture will continue to be limited
for the remainder of this time period; however, a shortwave is
progged to slide through the area Monday, which may bring additional
cloud cover. Otherwise, the only chance of precipitation will be
Monday night as WAA pushes into the region along and ahead of an
approaching warm front from the southwest. Again, moisture will be
limited so kept the coverage to isolated at this point.

Tuesday night through Wednesday night: Models are depicting a low
pressure system and 500mb trough sliding across central Canada to
northern Ontario during this time period. This would also allow a
cold front to slide through the area. Ahead of the front, southerly
flow will kick in, allowing temperatures to continue to be above
normal for Wednesday. Showers and thunderstorms are expected to
develop along and ahead of the front, with the best chances expected
Wednesday afternoon through late Wednesday night, before the cold
front passes to the east of the U.P. by late Wednesday night into
Thursday morning.

Thursday through the extended: The cold front will continue east of
the area Thursday morning with perhaps some lingering showers and
thunderstorms early in the morning over the far east.
Otherwise,abroad surface ridge will be in place across the Upper
Great Lakes Region with nearly zonal flow expected aloft. This will
keep temperatures near normal for this time period with fairly quiet

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 136 PM EDT SAT AUG 20 2016

With deepening low pres over ne WI crossing eastern Lake Superior
tonight, shra will continue. To the w of the low track, upslope
winds off Lake Superior should result in prevailing LIFR conditions
at KSAW into the evening hrs. KCMX should drop to IFR in the next
few hrs, but confidence is not especially high as northerly winds
will not be the ideal upslope direction for that terminal. KIWD
should see prevailing IFR conditions under a better upslope wind
direction. Overnight into Sun morning, expect gradual improvement
from w to e. KIWD/KCMX should break out to VFR around 12Z. At KSAW,
expect MVFR conditions to develop late tonight, but VFR may not
develop until near or just beyond this fcst period. Finally, closer
to the low pres track, gusty winds will impact KCMX/KSAW for much of
this fcst period with gusts as high as 30kt at times tonight.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 411 AM EDT SAT AUG 20 2016

A low pressure system, rapidly developing along the cold front
stretching across the central U.P. into Wisconsin, will track from SW
WI this morning, to near Green Bay this evening. The low will the
shift east of Sault Ste. Marie by Sunday morning. In response, NE
winds will increase to 25 knots through this afternoon. After the low
passes this evening, N to NNW gales to 40 knots are expected to
develop across the east half of Lake Superior. There could also be
some storm force gusts as high as 50 knots over south central and
eastern Lake Superior late tonight into early Sunday morning. As high
pressure then slowly builds in from the west through Monday, NW winds
will gradually diminish from around 30 knots Sunday morning to less
than 15 knots by Monday morning. A period of southerly winds of 10 to
20 knots is then expected Tuesday into Wednesday as the high pressure
drifts to the SE and low pressure develops over south-central Canada.

Upper Michigan...
  Beach Hazards Statement until 10 PM EDT this evening for MIZ005-

Lake Superior...
  Gale Warning from 5 AM to 2 PM EDT Sunday for LSZ251-267.

  Gale Warning from 8 PM this evening to 2 PM EDT Sunday for

  Gale Warning from 8 PM this evening to 11 AM EDT Sunday for

  Gale Warning from 2 AM to noon EDT Sunday for LSZ250.

Lake Michigan...
  Gale Warning from 11 PM this evening to 11 AM EDT Sunday for



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