Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 170522

Area Forecast Discussion
National Weather Service Marquette MI
122 AM EDT Thu Aug 17 2017

.SHORT TERM...(This evening through Thursday)
Issued at 351 PM EDT WED AUG 16 2017

A fairly active period of weather is expected over the next 24-36
hours a strong late summer low pressure crosses Upper Michigan.

After mostly dry conditions this evening, decent moisture transport
ahead of the main low will push a shield of moderate to heavy rain
with embedded storms northeastward across the CWA late tonight
through Thursday morning. Rainfall rates of 0.5in/hr will be
possible within this shield of rain.

Guidance continues to latch on to a narrow dry slot spreading over
the west half behind the main shield of rain. With plenty of low-
level moisture around, do not think this will be enough to cause
considerable clearing. However, some breaks in the clouds are
expected late morning into early afternoon. Shower activity will
also likely diminish, and possibly even end, for a 3-5 hour window
during this time across the west and central U.P.

As the stacked low drifts across the west half in the afternoon,
cloud cover and shower activity will increase. High mid-level lapse
rates of 7C/km combined with ample low-level moisture under the cold
core low will allow for MLCape values to increase to as much as
1000j/kg. With this set-up, pulse showers and some storms with heavy
rain are expected. 0-6km shear of 20-25kts and freezing levels of 9-
10kft may allow for some small hail with the strongest

Lastly, gusty SE winds are expected across the Keweenaw and east
half of the CWA. Inland gusts to 25mph and shoreline gusts to 30mph
are expected. This will produce a high swim risk for the beaches
along Schoolcraft County.

.LONG TERM...(Thursday night through Wednesday)
Issued at 351 PM EDT WED AUG 16 2017

Thursday night through Friday: As the surface low slides from the
central U.P. into Ontario through this time period, the associated
upper-level trough will slide into the area. The combination of
system forcing along with upslope flow and wrap-around moisture will
allow rain showers and cloud cover to linger through Friday
afternoon and early evening. Temperatures will be kept down with the
added cloud cover and precipitation, allowing most areas to see
highs only reaching into the mid to upper 60s with a 70 degree
reading possible over south-central locations. In addtion, the tight
pressur gradient between the extiting low and approaching high
pressure center will allow for breezy condtions acorss much of the
are through this time period.

Saturday and Sunday: As the upper-level trough and surface low
continue to shift eastward, upper level ridging and a suface high
pressure system are expected to build across the Upper Great Lakes
Region. This will allow winds to diminish across the area and allow
skies to become clear to partly cloudy through the weekend. There
may be a few afternoon showers that develop over the eastern U.P. on
any lake breezes that develop; however, the coverage should remain
isolated without any large scale systems impacting the area.

Monday through the extended: The next area of broader troughing will
shift eastward toward the Upper Great Lakes Monday afternoon through
the extended. As this happens, a cold front is expected to shift
into the area Monday afternoon and then slowly shift eastward into
Tuesday afternoon. As moisture, forcing and instability increase
along and ahead of the front, expect showers, thunderstorms and
cloud cover to increase across the area Monday afternoon through
Tuesday. The front will be east of the area on Wednesday allowing
condtions to dry out a bit; however, the upper level trough axis
nearby along with the potential for a shortwave passing through will
allow for increased cloud cover and possibly some pop-up afternoon
rain showers. Temperatures will be near normal for this time period.

.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 638 PM EDT WED AUG 16 2017

VFR conditions are expected at all sites through this evening. Then,
a shield of SHRA will spread northeastward across all sites
overnight through Thursday, resulting in deteriorating conditions at
all sites. Conditions will drop to LIFR/VLIFR at all sites on Thu.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 351 PM EDT WED AUG 16 2017

Easterly winds will increase into Thursday across central and
eastern Lake Superior as low pressure moves from the Central Plains
to the Upper Great Lakes. Across western Lake Superior, east to
northeast winds of 20-30 knots are expected through tonight,
especially along the MN shore into Duluth. Some gale gusts to 35
knots will be possible across eastern Lake Superior Thursday
afternoon. The winds will become NW on Friday as the low departs to
the east, with 20-30 knots expected for the east half. Lighter
winds, mostly under 20 knots, are expected over the weekend into
early next week with high pressure over the region.

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


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