Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 270928

Area Forecast Discussion
National Weather Service Marquette MI
428 AM EST Sun Nov 27 2016

.SHORT TERM...(Today and tonight)
Issued at 427 AM EST SUN NOV 27 2016

IR satellite imagery had indicated very minimal cloud cover coupled
with high pressure remaining overhead and also provided very light
winds. The combination has resulted in areas of dense fog developing
from south to north, mainly across the west/central portions of the
Upper Peninsula; however, expect pockets of dense fog to spread east
prior to daybreak. Compounding the problems early this morning will
be the fact that surface temps have also fallen below freezing. With
the fog overhead, this additional moisture will likely create some
slick conditions especially over untreated roadways. While fog is
expected to slowly improve above dense conditions after daybreak,
the challenge will be on how quickly the stratus cloud deck erodes.
The latest guidance would suggest minimal mixing taking place
through midday, which could signal the thermal inversion lasting
through the afternoon and trapping the shallow stratus layer into
the afternoon hours. Timelagged products have been steadily leaning
towards this stubborn scenario, so have steered the forecast in this
direction. In addition have also nudged temps cooler, or generally
in the upper 30s to possibly around 40 closer to the lakeshore

Then the focus for tonight turns towards timing and coverage of
precip ahead of a developed shortwave. A negatively tilted 500mb
ridge will amplify slightly over the Great Lakes this evening, which
will help to delay the moistening of the mid/upr levels of the
profile until after midnight. This should help to erode the leading
edge of the precip lifting north through Northern Wisc. Guidance is
in good agreement that around 9z Mon the mid-lvl ridge will push
east with precip steadily lifting northeast across the Upper
Peninsula. But with some dry air aloft, this could lower the
intensity of the rain to drizzle/lgt-rain. Temps aloft will remain
above freezing, so not expecting any p-type concerns tonight either.
Lows will likely not move much below afternoon highs.

.LONG TERM...(Monday through Saturday)
Issued at 427 AM EST SUN NOV 27 2016

Monday through Tuesday: To begin this period, a surface low pressure
system is progged to be positioned over western MN Monday with a
closed/vertically stacked 500mb low. Plenty of moisture will be
flowing into the U.P. along with isentropic upglide, which will give
a good chance of rain throughout the day Monday for most of the CWA.
Overall system dynamics are not overly impressive as shown by deep
layer Q-conv, but this will only act to keep the rain fairly light
overall. It does still look like rain will be likely throughout the
day. At this point wouldn`t expect more than a quarter of an inch of
rain or so at this point as output from most many of the models
suggest. Monday evening through much of the day Tuesday, the
moisture depth decreases across much of the west half of the U.P. as
the dry slot slides into the area. With very little forcing around
and the shallow depth of the moisture would expect the rain to
transition over to very light rain or possibly just drizzle. The
more significant issue Monday night through Tuesday morning will be
a reinforcing shot of energy that slides northeastward from the mid-
Mississippi Valley into Lower Michigan. This will develop another
strong low that slides across Lower Michigan by 12Z Tuesday and into
Southern Ontario By Tuesday afternoon. This system will be much more
dynamic and have much greater forcing over the eastern half of the
U.P. under the warm/moist conveyor belt. This will push PWAT values
up to around an inch, which is about 200-250 percent of normal.
Again, the moisture over the east half will be much deeper, keeping
definite rain in the forecast for the overnight Monday into the
Tuesday morning time period. QPF is being painted out over the east
half at or around an inch. The other component of this system will
be strong gusty winds Monday through Tuesday morning with Gales up
to 40 knots likely on the Great Lakes.

Tuesday night into Wednesday: The occluded front associated with the
aforementioned vertically stacked low pressure system will pass to
the northeast of the area Tuesday afternoon, taking most of the
deeper moisture with it. This should take most of the rain shower
activity out of the area; however, low cloud cover will still linger
across much of the CWA. There is another little shot of energy that
will slide east of the area, but it wouldn`t bring much more than a
few showers to the far east late Tuesday night into Wednesday
morning. Additionally, the occluded low will begin to slowly slide
toward the western U.P. by Wednesday afternoon, which will begin to
introduce precip chance over the far west once again. By that time,
cooler air will begin to move in aloft which may allow some snow to
mix with the rain at times over the far west.

Wednesday night through the extended: The closed low will slowly
meander through the Upper Great Lakes region through Friday night
before sliding to the east of the area over the weekend. As this
happens, colder air will begin to filter into the region, at the
surface and aloft, allowing the rain to transition to snow. The rest
of the extended looks to have several chances of lake
effect/enhanced rain/snow chances, but the exact locations will
depend on exactly where the surface features set up and the
associated wind direction. Currently it looks like the north to
northwest wind favored snowbelts would be most likely to see light
precipitation. It does look like temperatures overall will trend
colder during this time period and 850mb temperatures are progged to
cool to the -6C to -8C range.

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1236 AM EST SUN NOV 27 2016

The main forecast concern is with low clouds and fog potential
overnight into Sunday morning. Confidence in coverage remains a
concern; however, several sites in Northern Wisconsin are already
developing dense fog and it is expected this will steadily expand
north into the Upper Peninsula by 9z. Guidance has struggled with
handling of how low cigs will be reduced, but feel at least some
occasional IFR to LIFR near IWD/SAW and perhaps some slightly better
conditions at CMX. The weak southerly flow that downslopes into IWD
and CMX should help limit the fog potential. Expect fog to linger
just after daybreak, with likely seeing a thin stratus deck develop
and could take until midday before eroding completely.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 427 AM EST SUN NOV 27 2016

Weak ridge of high pressure will linger overhead today, resulting in
a light pressure gradient with winds less than 20kt through early
this afternoon from the south to souhteast. High pressure will shift
east this evening, with a low pressure deepening across the northern
plains into the upper midwest. This will result in a tight pressure
gradient developing across the Northern Great Lakes and creating
gales late this evening. Gales to 40kt are expected across all of
Lake Superior spreading west to east, but the gradient will slacken
earliest across the far west. Further east the gradient will remain
tight, with gales lingering through Mon night. The low pressure
system will linger over the upper midwest Tuesday into Wednesday;
however, the pressure gradient is not expected to be as tight and
allow winds to diminish below 25kt by Tuesday evening.

Upper Michigan...
  Dense Fog Advisory until 10 AM EST /9 AM CST/ this morning for

Lake Superior...
  Gale Warning from midnight tonight to 10 AM EST Tuesday for

  Gale Warning from midnight EST /11 PM CST/ tonight to 7 AM EST
     /6 AM CST/ Tuesday for LSZ240>242-245>248-263-265.

  Gale Warning from midnight EST /11 PM CST/ tonight to 10 AM EST
     /9 AM CST/ Monday for LSZ162.

Lake Michigan...
  Gale Warning from 4 AM Monday to 4 AM EST Tuesday for LMZ221-248-



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