Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 220717

Area Forecast Discussion
National Weather Service Marquette MI
317 AM EDT Tue Aug 22 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...(Wednesday through Monday)
Issued at 317 AM EDT TUE AUG 22 2017

Overall quiet weather is expected to prevail through the end of the
work week, and possibly through much of the weekend. Temperatures
will start off around 10 to 15 degrees below normal as cold air
advection drops south across the region on Wednesday; however,
expect temperatures to gradually modify back to near normal by this
weekend. While a fairly potent shortwave is progged to dig across
the Upper Great Lakes region Wednesday into Thursday, forecast
soundings show ample dry air across the region which should limit
any development of shower activity. The reinforcing shot of drier
Canadian air and ample radiational cooling on Wednesday night will
allow overnight lows to drop into the mid 30s across the interior
west, which will result in areas of patchy frost. Thursday through
the beginning of the weekend, surface high pressure will park across
the Upper Great Lakes leading to mostly clear skies and with no
precipitation expected.

This weekend, shortwave activity will dig across the Upper
Mississippi Valley increasing cloud cover from west to east by
Sunday. Models have backed off on the precipitation tracking west to
east across the area, with Saturday looking mostly dry and minimal
chances for precipitation through Sunday. Early next week, high
pressure looks like it will hold on; however, with the shortwave
finally making its way over the Upper Great Lakes region, there will
be a small chance for showers.

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 138 AM EDT TUE AUG 22 2017

Scattered showers and a few thunderstorms will remain possible into
the overnight hours then rain ends late. Conditions will continue to
lower to IFR or LIFR at IWD and SAW but should only fall to MVFR at
CMX. Conditions will steadily improve from west to east on Tuesday.
NW winds will gust over 20 kts at all the TAF sites on Tuesday as
drier air arrives.

.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...


LONG TERM...Ritzman
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