Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 181947

Area Forecast Discussion
National Weather Service Marquette MI
347 PM EDT Fri Aug 18 2017

.SHORT TERM...(Today and tonight)
Issued at 359 AM EDT FRI AUG 18 2017

Water vapor imagery shows troughing across the Upper Great Lakes
region this morning with the associated surface low tracking across
eastern Lake Superior. Upstream of the area, additional shortwave
activity is also apparent as it digs across the northern and central
Plains. A few lingering showers continued to impact portions of
Upper Michigan both ahead of and behind the main surface low. A few
areas of fog were observed across the area, primarily across the
Keweenaw Peninsula where upslope flow is most prevalent.

Today, as the above mentioned low pressure system continues to lift
northeast out of the area, cold air advection and lingering cloud
cover will help keep temperatures about 10 degrees below normal for
this time of year. Some locations, especially those downwind of Lake
Superior across the north central and eastern portions of Upper
Michigan will struggle to climb into the mid 60s. In fact, some
locations may see high temperatures occur this morning, with a
cooling trend through the afternoon. Given the track of the system,
it looks like we will see more northwesterly than northerly winds on
the back side of the system. Given this flow orientation with the
terrain, this should limit the temporal extent of any lingering
drizzle chances across the north central portions of the area to at
least the morning hours. Across the Keweenaw where upslope flow will
be better oriented with the terrain, expect the fog to linger across
the higher terrain this morning and possibly into the early
afternoon hours. Further east, wrap around showers will linger
through a good portion of the day. Not expecting widespread showers,
but a few locations may pick up a tenth to a quarter of an inch of
additional rainfall. As the pressure gradient and pressure rises
behind the exiting system linger across the region, expect winds to
be rather gusty today. These gusty winds will be strongest near the
shores of Lake Superior and will create a high swim risk for
Marquette and Alger counties.

Late this afternoon through the overnight hours, as the upstream
shortwave activity previously mentioned begins to dig across the
Upper Great Lakes region, it isn`t out of the question that we could
see scattered showers track southeast across the area.

.LONG TERM...(Saturday night through Friday)
Issued at 346 PM EDT FRI AUG 18 2017

Saturday night and Sunday: Weak upper level ridging and a surface
high pressure ridge are expected to build across the Upper Great
Lakes Region for Saturday night into Sunday morning. This will allow
winds to diminish across the area and allow skies to become clear to
partly cloudy through Sunday morning. Sunday afternoon a weak
surface trough is expected to slide in from the west in response to
a shortwave moving through NW Ontario, which will spread scattered
showers and thunderstorms into the west half of the U.P. mainly late
afternoon through the evening hours. Sunday afternoon will be very
warm ahead of the surface trough with mixing of around 18c temps
from h85 thermal ridge overhead to sfc resulting in many locations
warming into the mid 80s.

Monday into Tuesday: The next area of broader mid-level 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 (MLCAPEs approach
1000 j/kg) increase along and ahead of the front, expect showers,
thunderstorms and cloud cover to increase across the area Monday
afternoon into Tuesday. Also not out of the question there could be
some isolated severe storms Mon afternoon into evening given
instability and deep layer shear increasing to 30-35 knots.

Wednesday: With the broad mid-level trough still lingering over the
area and the models hinting at another shortwave moving down from
Ontario, scattered showers could persist into Wed. The 12z ECMWF and
CMC models also suggest the potential for some lake enhancement to
showers on Wednesday as h85 temps fall near 7C Wed afternoon. Given
mid-lake Superior temps 15-16C this would create a lake-h85 delta-t
of around 8C. With a possible shortwave moving through the area
could see a hybrid of lake enhanced and diurnal instability showers.

Thursday and Friday: Should see a drying trend toward the end of
next week as broad sfc ridging builds in fm northwest of the lake.
Temperatures will likely be below normal for the latter half of the
work week.

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 144 PM EDT FRI AUG 18 2017

MVFR ceilings are expected to steadily improve this evening at each
of the TAF sites. KIWD and KCMX will be first to improve this
afternoon as drier air filters in at the lower levels of the
atmosphere. KSAW will be closer to the departing low pressure
system, which will keep the low level moisture lingering a bit
longer; however, the west to northwest downsloping wind will help to
scour out some of the lowest clouds. Skies will likely clear over
the western TAF sites tonight, which may lead to some fog
development late tonight; however, confidence in fog development is
low enough at this point to leave out of this TAF issuance.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 359 AM EDT FRI AUG 18 2017

Today, as low pressure continues to lift northeast across eastern
portions of Lake Superior and up into Canada, expect winds behind
the system to be 20-30 knots across the central and eastern portions
of the lake. A few gale force gusts will be possible, especially
closer to the lake shore where winds may become locally enhanced.
Further to the west, winds will begin to relax through the afternoon
to around 10 to 20 knots.

Tonight as the pressure gradient relaxes across the area, expect
winds to decrease to around 10 to 20 knots. Winds are expected to
remain below 20 knots through the weekend and a good portions of
next week.

Upper Michigan...
  Beach Hazards Statement until 9 PM EDT this evening for MIZ005-

Lake Superior...
Lake Michigan...


SHORT TERM...Ritzman
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