Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 180001

Area Forecast Discussion
National Weather Service Marquette MI
801 PM EDT Thu Aug 17 2017

.SHORT TERM...(This evening through Friday)
Issued at 332 PM EDT THU AUG 17 2017

Latest 19z WV imagery and RAP analysis indicated a vigorous
mid/upper level low over far NW WI fast approaching western Upper
Mi. Radar imagery shows increasing shower coverage as forcing
ahead of the mid-upper low combines with MLCAPE values 500-1000
j/kg highest over Menominee County. Instability has also led to
a few isolated t-storms.

Into this evening, radar trends and short range high res models
suggest showers continuing into the evening hours along
with some isolated t-storms into early evening. The main threat
will be for heavy rainfall of several inches with any stronger
slow moving shra/tsra clusters as PWAT values climb into the
1.50-2.00 inch range. Even though effective shear will be weak
(generally 25 knots or less), with the strong vorticity center
moving into the area combined with modest instability there may
be a slight potential for a brief/weak funnel/tornado similar to
what occurred over srn MN yesterday afternoon and evening.

Tonight, as the mid level low lifts to the northeast, the heavier
shra/tsra will diminish by late evening. Additional lighter wrap-
around rain/drizzle will develop over the northwest half especially
where upslope nnw flow/lift is strongest.

Friday, Some isolated showers could linger into the morning hours
especially for nw upslope locations but then as low continues to
lift ne expect drying and partial clearing from the west in the
afternoon. NW winds will remain fairly gusty through much of the
day especially north central and east where gusts of 25-30 mph can
be expected. 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. Farther west and for downsloping locations south central
in nw flow, high temps Fri could reach into the lower 70s with the
possibility of afternoon breaks in cloud cover.

.LONG TERM...(Friday night through Thursday)
Issued at 332 PM EDT THU AUG 17 2017

Saturday and Sunday: As the upper-level trough and surface low
continue to shift eastward, weak upper level ridging and a suface
high pressure system are expected to build across the Upper Great
Lakes Region for Saturday into Sunday morning. This will allow winds
to diminish across the area and allow skies to become clear to
partly cloudy through Sunday morning. 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 for the day
Saturday. Sunday afternoon a weak surface trough is expected to
slide in from the west, which will bring scattered showers and
thunderstorms from west to east across much of the U.P. through the
evening hours. Sunday afternoon will be very warm ahead of the
surface trough with many locations warming into the mid 80s.

Monday into Tuesday: The next area of broader troughing will shift
eastward toward the Upper Great Lakes for this time period. 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.

Rest of the extended: 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 at least increased afternoon cloud
cover and possibly some diuranl afternoon rain showers. Temperatures
will be near normal for this time period. At this point, will stick
with a consensus of the models for this time period.

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 800 PM EDT THU AUG 17 2017

Upslope, moist flow on the back side of a surface low pressure
system currently near KSAW will promote low CIGs, rain and reduced
VIS at all sites into Friday morning. Gradual improvement from W to
E will be noted on Fri as the low exits the region.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 332 PM EDT THU AUG 17 2017

Easterly winds could briefly gust to low end gales to 35 knots over
far eastern Lake Superior into late this 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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