Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 200658

Area Forecast Discussion
National Weather Service Marquette MI
258 AM EDT Sun Aug 20 2017

.SHORT TERM...(This evening through Sunday)
Issued at 349 PM EDT SAT AUG 19 2017

Main concerns in the short term forecast will be the potential for
very warm high temperatures Sunday, along with showers and
thunderstorms moving in from the west during the mid to late
afternoon hours.

Tonight: Evening showers and thunderstorms will diminish across the
south-central and eastern U.P. as daytime heating diminshes and lake
breeze boundaries fade. Some stronger storms are still possible
through late this afternoon into the early evening hours. This would
be mainly along the boundaries in the greater shear areas. Small
hail and gusty winds would be the main threat, again, this would be
early in the evening. Added support early in the evening would come
from a very subtle/weak shortwave brushing past the east half of the
area. Otherwise, the rest of the night should remain fairly quiet as
weak upper-level ridging builds in across the area from the west.
Winds will be fairly light as the pressure gradient remains fairly
light. This will allow radiation cooling to occur, causing at least
patchy fog to develop over the west half of the U.P. and especially
in areas where rainfall occurred this afternoon and evening.
Overnight lows will be in the 50s across most area; however, areas
along Lake Superior may stay in the 60s as downsloping winds develop

Sunday: The first half of the day will continue to be fairly quiet
across the U.P. as the upper-level ridge and surface ridge begin to
shift eastward. This will allow an upper-level trough and associated
cold front to shift slowly eastward into the west half of the U.P.
during the afternoon hours. Showers and thunderstorms are expected
to develop along and ahead of the cold front as both forcing and
instability increase. Instability values ahead of the front are
progged to be in the 1000-1500 J/kg range as dewpoint jump into the
low 60s. A couple strong to isolated severe thunderstorms are
possible ahead of the cold front as shear values are progged to 25
to 35 knot range orthogonal to the front, lending support to storm
organization. At this point, it looks like the main threat would be
small hail and gusty winds in the strongest thunderstorms. The east
half of the area should remain dry through much of the afternoon as
a CAP remains in place. This capping, along with mostly sunny skies
and downsloping winds, will allow temperatures to warm into the 80s
for most locations. The exception will be along Lake Michigan where
south winds will help to cool temperatures due to the marine
influence. The warmest tempertures will likely occur along Lake
Superior due to downsloping southerly winds. Temperatures in those
areas may warm as high as the upper 80s and a 90 degree reading
would not be totally out of the question.

.LONG TERM...(Monday through Saturday)
Issued at 258 AM EDT SUN AUG 20 2017

Overall, the weather looks to remain active, especially across the
south central and eastern portions of Upper Michigan through early
parts of the week. Then as high pressure drops down across the Upper
Great Lakes region, cooler and drier air will advect south across
the area for the middle and end of the work week.

Monday, the cold front that is progged to drop southeast across the
area Sunday into Sunday night will stall out just to our south.
Therefore, the best precipitation chances look to remain south of
the area across Wisconsin and lower Michigan. As drier air begins to
filter in behind the front, things are looking a bit better cloud
cover wise for the viewing of the partial solar eclipse on Monday
afternoon, especially across the north central. Late Monday into
Tuesday, as longwave troughing digs across the Upper Great Lakes,
the stalled out front will lift back northward. This will allow
chances to increase for showers and thunderstorms Monday night.
There is some uncertainty in how far north this front and the better
instability will get; however, chances still look best across the
south central and eastern portions of Upper Michigan. Tuesday
morning, lingering showers and thunderstorms will push east-
southeast across the area eventually vacating Upper Michigan as a
stable post-frontal air mass works its way into the region.

Wednesday through the end of the work week the weather looks to
remain quiet as surface ridging takes hold on the Upper Great Lakes
region as longwave troughing anchors across the northeast. Wednesday
looks to be the coolest day of the week, with temperatures in the
60s, as cold air advection will continue to spread southward.
Overnight lows will be rather chilly as well, with a few interior
locations across the west and central possibly seeing temperatures
drop down into the upper 30s early Thursday morning. Thursday
through Friday, temperatures will rebound a bit each day as the
better cold air advection shifts east of the region, and warm air
advection gradually returns. Temperatures will return to near normal
through the weekend as warm air advection increases through ahead of
the next system dropping down across the north central CONUS. The
best precipitation chances this weekend look to be on Sunday.

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 138 AM EDT SUN AUG 20 2017

VFR conditions expected through end of TAF period. S winds may gust
over 20 kts on Sun afternoon at SAW and there could be scattered
showers or thunderstorms at all the TAF sites late Sun aftn into
early Sun evening as a cold front crosses the region.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 349 PM EDT SAT AUG 19 2017

Winds will remain at or below 20 knots through the first half of the
work week as the pressure gradient remains fairly weak across Lake
Superior. South winds may gust close to 25 knots Sunday afternoon as
a cold front slides through, but it should be for a short duration.
The next chance for gusty winds will be Wedensday as low pressure
slides to the northeast of Lake Superior. Northwest winds may gust
as high as 30 knots during that time period.

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


LONG TERM...Ritzman
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