Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 212007

Area Forecast Discussion
National Weather Service Marquette MI
407 PM EDT Mon Aug 21 2017

.SHORT TERM...(This evening through Tuesday)
Issued at 407 PM EDT MON AUG 21 2017

Tricky forecast through the late evening hours with respect to
developing convection or potential convective development. These
issues are a result of the typical variances as expected with
convective allowing models. In this case, there are several areas of
convection ongoing to the south and west of the U.P.

Water vapor imagery shows a trough digging into the Northern Plains
this after along with ongoing convective complex over southern MN.
Visible satellite imagery shows extensive cloud cover to the west of
the U.P. and well south of the area, over southern WI. Most of the
U.P. has seen partly cloudy skies through most of the day; however,
the cloud cover is steadily increasing from the west. Radar imagery
is showing a convective complex lifting northeastward from northern
IA into southern MN.

Late this afternoon through Tonight: A weak stationary front
stretching across much of northern WI, eastward across northern
lower MI is expected to lift northward this evening as a warm front.
This will be a result of a strengthening low pressure system over
the Central Plains lifting northeastward toward the eastern U.P. As
the warm front lifts northward late this afternoon into this
evening, WAA and moisture will increase across the area. This will
cause showers and thunderstorms to develop across much of the area.
The greatest thunderstorm potential will be for the central and east
half of the area through late evening, where instability values are
expected to increase to around 500 - 1000 J/kg. Effective shear
values along and just south of the warm front, will increase to
around 30 to 35 knots, which may lead to a few strong to severe
thunderstorms. The main threat from these thunderstorms would be the
potential for hail. This will be mainly over the southeast half of
the U.P. Heavier rain is also a possibility as an FGEN band is
progged to develop and shift from west to east across the area. The
best chance for a steadier heavy rainfall will be across portions of
the central into the western portions of the area in the evening,
then shifting eastward across the rest of the area late evening into
the overnight. PWAT values are progged to be around 1.5 inches over
the central and east through this evening. Drier air will filter in
from the west overnight tonight, effectively putting an end to the
rain showers from west to east.

Tuesday: The surface low will shift farther north and east of the
area throughout the day, again, leading to a decrease in any
lingering rain showers over the far east portions of the U.P. early
in the morning. At the same time, the upper level 500mb trough axis
is expected to shift directly overhead. This will likely lead to
some afternoon CU along with the possiblity of a couple of isolated
showers during the afternoon hours. This will also result in more
mixing during the day, keeping temperatures cooler that the past
couple days.

.LONG TERM...(Tuesday night through Monday)
Issued at 316 PM EDT MON AUG 21 2017

Pretty quiet stretch of weather expected for the second half of he
work week. Cool Canadian high pressure will settle over the Upper
Great Lakes with early fall-like temperatures expected Wednesday
into Thursday. Under clear skies and light winds...ideal radiational
cooling conditions will allow temperatures to fall into the mid and
upper 30s over parts of the interior west Wednesday night.  Some
patchy frost in those normally colder locations is not out of the
question. With warm advection pattern returning for the
weekend...there could be a few showers around but temperatures will
moderate back to normal.

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 407 PM EDT MON AUG 21 2017

VFR conditions are expected through early this evening. Showers will
move into each of the TAF sites late this afternoon into this
evening and then linger into tonight. Thunderstorms area also
possible across KIWD and KSAW in the evening before turning to more
of a plain rain shower event. Ceilings will drop to IFR at times
tonight as low pressure and increase low level moisture moves
through the area. Conditions will steadily improve from west to east
late tonight through Tuesday.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 407 PM EDT MON AUG 21 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. The next chance for gusty winds will be Tuesday night into
Wednesday as low pressure slides to the east of Lake Superior.
Northwest winds may gust as high as 30 knots during that time period.

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


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