Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 190521

Area Forecast Discussion
National Weather Service Marquette MI
121 AM EDT Sat Aug 19 2017

.SHORT TERM...(This evening through Saturday)
Issued at 349 PM EDT FRI AUG 18 2017

Tonight: Wrap-around moisture will continue to flow into much of the
central and eastern portions of the U.P. this evening, before slowly
exiting off to the far eastern portions of the area overnight. In
addition to the wrap-around moisture, another shorwave rounding the
base of the overall troughing pattern will slide across the U.P.
This may touch off some early evening showers over the far western
U.P.; however, instability is fairly minimal due to the continued
cloud cover across the area, so this would likely be limited to any
showers that form over MN and slide into the far west. Otherwise, as
the shortwave shifts eastward tonight, skies should begin to clear
over the west half. If the clearing occurs early enough, radiational
cooling may allow some patchy fog to for overnight over the west
half. Temperatures will be kept a bit warmer over the east where
cloud cover is likely to linger through much of the night.

Saturday: The main trough axis will continue to shift eastward
through the day Saturday allowing for a steady warming trend across
the area. This will especially be true across the west half under
the approaching ridge. The east half, still remain under the
influence of the departing trough, will see some isolated to
scattered afternoon showers and thunderstorms develop along lake
breeze boundaries. There will be some additional support, steeper
lapse rates, from yet another shortwave progged to slide across the
east half during peak heating. Again, the main focusing mechanism
will be the lake breeze boundaries over the east half, so the
showers and thunderstorms should be limited to those areas. CAPE
values are expected to be in the 500-800J/kg range across the south
central and east along with shear values in the 25 to 35 knot range.
This may allow for a couple stronger storms to develop along the
boundaries, especially at the onset of thunderstorm development. The
main threat would be hail and gusty winds. The rest of the U.P. may
only end up seeing some afternoon CU. High temperatures will warm
into the mid to upper 70s across most of the area with a few 80
degree readings possible.

.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 06Z TAFS through 06Z Saturday night)
Issued at 120 AM EDT SAT AUG 19 2017

VFR conditions are expected through the TAF period. There is some
fog developing over the western U.P. but that is expected to stay
out of KIWD.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 349 PM EDT FRI AUG 18 2017

Northwest winds will gust to 20 to 30 knots over the easter portions
of Lake Superior through early this evening as the pressure gradient
slowly relaxes across the area. Winds will then remain at or below
20 knots through the first half of the work week.

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


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