Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 240902

Area Forecast Discussion
National Weather Service Marquette MI
502 AM EDT Sun Sep 24 2017

.SHORT TERM...(Today and tonight)
Issued at 457 AM EDT SUN SEP 24 2017

WV imagery and RAP analysis indicated an amplified pattern with a
mid/upper level trough over the wrn CONUS and a ridge from the
ern Great Lakes into the mid Atlantic resulting in ssw flow from
the cntrl plains into the upper Mississippi Valley. At the
surface, a stationary front extended from nrn and wrn Lake
Superior into cntrl MN. Areas of shra/tsra remained mainly to the
west of the cwa from the ern Dakotas to nrn MN. Some isold light
showers were lifting through cntrl Lake Superior but remained weak
and unorganized.

Today and tonight, Strengthening srly low level flow ahead of the
ern Dakotas trough will push the portion of the front over Lake
Superior farther north today. Subsidence/capping will be strong to
suppress shra/tsra chances, keeping the pcpn to the north and west.
However, Gradually falling heights and a slowly advancing front will
gradually slide eastward may allow some shra/tsra into the far west
near IWD late tonight.

Even with a strong subsidence inversion near the 590 DM ridge
over the cntrl/ern Great Lakes, forecast mixing through 850 mb
temps around 18C will support readings in the upper 80s over much
of the area except downwind of Lake Michigan. Adding to the
discomfort will be dewpoints remaining in the 60s. Low temps
should also remain in the upper 60s with some downslope locations
around 70.

.LONG TERM...(Monday through Saturday)
Issued at 411 AM EDT SUN SEP 24 2017

Monday through Tuesday night: As the surface low shifts from MN into
Ontario through this time period, expected a very slow moving cold
front to drift into the western U.P. Monday. The front will pick up
speed late Monday night into Tuesday ahead of the approaching deep
trough from the west. A continued very moist environment ahead of
the cold front and the initially very slow movement of the front
will allow for the potential of heavy rainfall across much of the
CWA. PWAT values are progged to be around 1.5 inches or roughly 200
percent of normal for this time of year. Widespread severe weather
is not expected with the frontal passage, so the heavier rain
potential will be the main threat for this time period. The area
that will likely see the greatest totals, up to an inch, will be
over the western portions of the U.P. where the front will progress
the slowest. Temperatures will continue to be above normal for both
Monday and Tuesday; however, the trend will be more toward normal
temperatures by Tuesday afternoon, coolest for western portions of
the Upper Peninsula.

Wednesday through Friday: A bit drier air will push into the area
for Wednesday, which should lead to mainly dry conditions across
much of the area under near normal temperatures in the upper 50s to
around 60. Wednesday night through Friday, models continue to have
differing solutions on how strong the next wave of energy will be as
it rotates into the Upper Great Lakes. The GFS is not as strong and
much quicker with move the wave through the area, while the EC is
much stronger and more persistent in keeping deep troughing across a
good portion of the eastern CONUS. The Canadian model shows a very
similar trend to the EC, which have both been showing a similar
setup over the past few model runs. This lends more credibility to
keeping cooler temperatures along with rain showers and increased
cloud cover across much of the area. The system forcing will
initially be the cause for rain showers; however, cooler air aloft,
associated with the trough, will allow 850mb temperatures to
potentially drop below zero by late Friday afternoon resulting in an
increased lake effect rain shower component through Friday night.
Outside of the rain shower potential, temperature will cool off
significantly from where they`ve been over the past couple days. In
fact most places will be near to below normal by the end of the work
week. High temperature will fall into the low to mid 50s by the ind
of the work week.

Rest of the extended: The trough will begin to progresses eastward
through Sunday, allowing for warming temperatures aloft along with
drier air to filter into the area. This should lead to a diminishing
trend in the rain shower potential along with a steady warming trend
toward the end of next weekend.

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 147 AM EDT SUN SEP 24 2017

There is a chance of fog tonight at KCMX and maybe KIWD. Did not
have enough confidence in fog at KIWD, so left it out there.
Otherwise, VFR conditions are expected.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 501 AM EDT SUN SEP 24 2017

Low to mid 60s dewpoints sliding across Lake Superior are expected
to linger into Tue bringing patchy to areas of fog across the lake.
Some of the fog could be locally dense at times. Expect winds to
generally be below 20 knots through the early part of next week
under a weak pressure gradient. However, as a cold front moves
across Lake Superior Tue night into Wed with colder air moving in,
wind gusts will increase to 20 to 30 knots.

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


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