Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 200427

Area Forecast Discussion
National Weather Service Marquette MI
1127 PM EST Thu Jan 19 2017

.SHORT TERM...(This evening through Friday)
Issued at 347 PM EST THU JAN 19 2017

Warmer than normal temperatures will continue through the short-term
forecast, but a neg-tilt shortwave trough lifting north through the
Southern/Central Plains tonight into Friday will bring a chance for
some light precipitation to mainly the southwest two thirds of the
cwa on Friday. Most the precipitation will fall as rain, but there
could be some freezing rain Fri morning, mainly along the Wi border
counties. With the influx of higher dewpoints and moisture into the
area, stratus and patchy fog will continue to be an issue later
tonight into Friday...especially for those locations favored by an
upslope/onshore se flow.

Ridging aloft and at the sfc will maintain dry conditions through
much of tonight. However, model soundings suggest lingering low-
level moisture will remain trapped under the strengthening
subsidence inversion. This will result in more stratus/patchy fog
for much of the forecast tonight. Suspect only locations favored by
a downslope southerly flow, mainly those locations along Lake
Superior, could stay free of stratus and fog tonight. With models
trending slower with the arrival of the Plains shortwave, expect
mostly dry conditions tonight across the cwa.

Friday, a weakening negatively tilted shortwave will be lifting into
the Upper Lakes. Despite negative tilt, only modest forcing/weak
isentropic ascent are indicated by models to swing thru Upper MI.
This should lead to some -ra lifting slowly across the area Fri.
However, with temps below freezing tonight, pcpn may start out as
light fzra in the morning for the Wi border counties, although
models still a bit uncertain on arrival of pcpn. Given uncertainty
with pcpn timing decided not to issue a WSW headline, but I did
issue a SPS for light freezing rain potential. Expect any freezing
rain to change over to rain by afternoon. With expected rain and
dewpoints continuing to increase, fog and stratus will again plague
much of the area on Friday. Patchy dense fog will be possible along
Lake Mi counties and for those locations favored in upslope se flow.
Clouds and rain should keep max temps generally in the 30s.

.LONG TERM...(Friday night through Thursday)
Issued at 302 PM EST THU JAN 19 2017

January thaw with well above normal temperatures continues into
early next week. Mid to late next week as strong jet stream crossing
northern Pacific attm pushes across the Conus, deep upper level
troughing will become established across much of the Conus. Temps
will only return toward normal as this colder air moves back over
much of the Conus. Lift with shortwaves over the central Conus this
weekend into early next week along with persistent low-level lift
ahead of sfc troughing from the central Plains to the Ohio Valley
will result in off and on rain chances this weekend into Mon and
depending on low-level temp profile, there could be freezing
precip issues as well. Colder air with the increasing troughing
brings snow back into the picture beginning late Monday night or
into Tue. Models have been hinting at more well developed
shortwave and associated low pressure system lifting across Great
Lakes Tue into Wed on leading edge of the troughing and colder
air, but they still do not agree in how strong this system will be
and the exact track of sfc low.

On Fri night, shortwave currently bringing showers to western
portion of Ohio Valley will be in process of lifting across northern
Upper Michigan and Lk Superior as shown by h7-h5 q-vector
convergence and moist isentropic ascent 295-285k (925-700mb). Expect
batch of light rain across mainly northern Upper Michigan in the
evening. Ptype should stay liquid as blyr temps will be middle to
upper 30s. Once rain ends temps could try to drop toward freezing
which may lead to slippery spots developing overnight. There could
also be some fog or drizzle, especially in areas of central Upper
Michigan where SE winds will lead to upslope lifting. Another
shortwave coming out of the trough over the western Conus lifts
across Upper Michigan on Sat. Also should be another round of low-
level isentropic lift as sfc low pressure wave lifts toward the
Upper Mississippi river valley while weakening. Will have to watch
out for possible freezing rain/drizzle Sat morning as warm temps
aloft flow over sfc-1kft layer that could be just blo freezing.
Similar to Friday the freezing precip hazard will diminish as blyr
temps warm into the mid-upper 30s on Sat aftn. Could be slippery on
untreated roads in the morning though.

Yet another shortwave moves across Upper Great Lakes on Sun though
much stronger shorwtwave/sfc low should be more over southern Plains
to the Tennessee river valley. More low-level lift along sfc trough
extending to the northwest of the southern Plains system and high
pressure over eastern Canada will support some light rain or at the
least increase the drizzle potential. Blyr temps on Sun should be
high enough to decrease freezing precip potential, though with even
slight cooling on Sun night could see that hazard return to inland
areas of central and east. On Mon as the system over the southeast
Conus heads to the east coast, expect sfc trough to persist across
the Great Lakes before it meets up with secondary sfc low over the
northern Plains. This low-level lifting mechanism along with another
shortwave lifting northward over the middle Conus and stronger jet
energy crossing middle Conus should help light rain expand over
Upper Great Lakes. Freezing precip could be factor on Mon morning
before temps warm by aftn into the mid to upper 30s.

All through the weekend and into Mon, ongoing light liquid precip,
melting snowpack and sfc dwpnts rising above freezing should result
in areas of fog, especially over the higher terrain of the central
cwa and the Keweenaw with steady ESE-SE wind direction. Fog could be
dense at times.

As shortwave slides across Upper Great Lakes into Tue, expect
cooling aloft to allow for rain/snow mix later Mon night with better
chance of snow on Tue as heights aloft fall and overall column
cools. Whether there is stronger system to bring accumulating snow
to much of region later Tue into Wed is not clear yet. Current runs
all show stronger system across middle Conus on leading edge of
larger scale troughing developing. But, as would be expected this
far out in time, there remains disagreement on track of low. ECMWF
favors track from northern Ill toward Lk Erie while Canadian is more
suppressed and GFS is more wrapped up and farther northwest. Even if
this system does not bring widespread snow to Upper Michigan, it
will still help switch the mild weather pattern back to one that is
breezy and cooler by this time next week. Colder conditions with
readings possible back or even blo normal could come back in by the
weekend of Jan 27-29.

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1127 PM EST THU JAN 19 2017

Very challenging aviation forecasts at the TAF sites this period
continues. Trapped low level moisture below a fairly strong
temperature inversion, will keep fairly low ceilings (VLIFR) in
place at SAW and will move back into CMX. More moisture moves in
late tonight and Friday, which should ensure lowering ceilings and
visibilities for each of the TAF sites through Fri night.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 347 PM EST THU JAN 19 2017

A relatively weak pressure gradient over the Upper Great Lakes in
the absence of any strong weather systems will result in winds under
20 kts over Lake Superior most of the time into early next week.

Upper Michigan...
  Dense Fog Advisory until 11 AM EST /10 AM CST/ Friday for

Lake Superior...
Lake Michigan...


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