Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 170814
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
414 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
showers/storms.

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...(Friday through Wednesday)
Issued at 413 AM EDT THU AUG 17 2017

A fairly progressive pattern will prevail over the next 7 days. Very
well-defined shortwave currently lifting toward the Upper Great
Lakes will reach Quebec/New England on Sun. Meanwhile, the next trof
which arrives over western Canada Fri will reach central Canada
early next week and will then be in the Hudson Bay to Great Lakes
region on Tue. Longer range guidance is in quite good agreement that
the pattern should then slow down/become much more amplified across
Canada again as sharp ridging rebuilds over central Canada by late
next week. This will result in the trof over the Hudson Bay to Great
Lakes region on Tue amplifying over eastern N America during the
last half of the week. These large scale changes will lead to cool
conditions over the next couple of days as approaching trof crosses
the area. Temps will then swing above normal over the weekend ahead
of approaching cold front tied to the trof reaching central Canada.
As that trof then goes on to amplify over eastern N America, temps
will fall back, and there will probably be at least a couple of days
of blo normal temps during the last half of next week. As for pcpn,
wet period today into Fri associated with passing trof will give way
to a dry weekend for most of the fcst area. The next potential of a
more widespread pcpn event should arrive Mon into early Tue in
association with the cold front tied to the trof progressing from
central Canada to the Great Lakes region and Hudson Bay. Drier
weather will return late Tue thru Thu, but the amplifying trof over
eastern N America raises some concern for diurnally driven isold/sct
convection as summertime nw flow over the area is notorious for that
kind of activity.

Beginning Fri, sfc low pres will be exiting to the e of Lake
Superior/Upper MI during the morning. Wrap around/upslope enhanced
shra affecting much of the area early in the morning, except the s
central, will end from w to e during the day into the evening. It
will be a breezy day behind the rather vigorous low pres system for
Aug. NW winds will likely be gusting frequently into the 15-25mph
range from the Keweenaw to central and eastern Upper MI. Gusts up to
30 mph will be possible along the lakeshore over n central and ne
Upper MI. These blustery winds will lead to large waves and a high
swim risk for the Lake Superior beaches of Marquette and Alger
counties on Fri. However, it won`t be a day to go to the beach due
to clouds/shra and temps struggling to get out of the lower 60s over
the n central and ne fcst area where shra/cloud cover will be most
persistent. Not out of the question that a few locations will fail
to get above 60F if shra/clouds persist thru the daylight hrs. Over
the w and sw fcst area, temps may reach 70F, aided by some breaks in
the cloud cover during the aftn. Trailing shortwave dropping into
the departing trof late Fri night will probably prevent skies from
completely clearing out. Could even be a few sprinkles over the w
late Fri night.

Although potential is very low, passage of the trailing shortwave on
Sat may lead to isold -shra or a few sprinkles. Otherwise, expect a
partly cloudy, warmer day with temps rebounding back to normal or
even slightly above normal Sat aftn.

Trof moving across western Canada Fri will evolve into a broad mid-
level low over central Canada on Sun. Shortwave swinging around the
s and se side of the low will push associated cold front toward the
Upper Lakes late in the day, and it may spark a few shra/tsra over
the w. Ahead of the front, expect a warm day Sun with highs in the
80s, except e along Lake Michigan.

As the mid level low w of Hudson Bay drifts e, a shortwave will
amplify troffing into the Great Lakes by Tue. This additional energy
should support an increase in shra/tsra coverage along frontal
boundary and across Upper MI for Mon, perhaps lingering into Tue.
Dry weather should mostly follow for Wed/Thu. However, nw flow in
addition to the potential of shortwaves to drop se across area could
generate mainly diurnally driven isold/sct convection.
&&

.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.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
  Beach Hazards Statement through this evening for MIZ014.

Lake Superior...
None.
Lake Michigan...
None.
&&

$$

SHORT TERM...Kluber
LONG TERM...Rolfson
AVIATION...07
MARINE...Kluber


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