Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 202251

Area Forecast Discussion
National Weather Service Marquette MI
551 PM EST Fri Jan 20 2017

.SHORT TERM...(This evening through Saturday)
Issued at 310 PM EST FRI JAN 20 2017

Murky conditions over much of Upper Michigan today with moist
easterly low-level flow to the north of weakening sfc low pressure
system over Ohio Valley. Shearing out shortwave trough and area of
isentropic lift is leading to slow northward push of light rain into
southern Upper Michigan. Despite temps at or blo freezing this
morning as the rain moved in, there were not many icing issues
reported as main roads were mostly wet. Cold ground temps likely led
to slippery non treated surfaces as was occurring over northern WI.
As weakening shortwave continues to drift north expect the shield of
steady light rain to do so as well. Should be pretty rainy evening
for northern Upper Michigan but the rain should taper off by late
evening or after midnight. Due to the moisture from the rain that
will have occurred and/or potential light drizzle at times, temps
falling into the low to middle 30s could lead to icy conditions on
untreated surfaces tonight. Plan to cover this with special weather
statement and mention in the hazardous weather outlook.

On Sat, the damp and murky conditions will continue. Temps will rise
into the upper 30s or near 40 by the aftn. At this point, with
minimal insolation, thinking 40 will be a stretch. Low level flow
remains weak as weakening area of low pressure lifts toward Upper
Mississippi river valley and warm front slides to the western Great
Lakes. Another shortwave currently over the central Plains lifting
in along with the low-level forcing/lift should enhance light rain
especially in the aftn. May see drizzle at times before the next
surge of rain on Sat. Since sfc temps will be around freezing could
still see icy conditions at times on untreated sfcs at least during
the morning hours.

Other larger issue is fog. Fog was very widespread near Lk Michigan
and the Bay of Green Bay into early aftn with widespread reports of
vsby less than 1/4sm. Fog has lifted this aftn though with vsby now
more in the 1-3sm range as the more widespread rain moved in,
scouring out the tiny fog droplets. However, weak east to southeast
low-level flow and sfc temps/dwpnts above freezing flowing across
ice on Bay and sfc temps in the mid 30s over the open waters of Lk
Michigan should result in more dense fog forming again near Lk
Michigan by this evening as the steadier rain lets up. Moist ESE
flow and an ongoing melting snowpack will likely allow this fog
to expand over much of cntrl Upper Michigan and across the
Keweenaw later tonight (especially once the rain ends) and similar
wind trajectories and dwpnts on Sat indicate the fog could
persist through much of the day. Went with dense fog advy for all
but far western cwa (since downslope E-SE flow not as favorable
there) through midday Sat. Widespread dense fog probably will not
develop until after the steady rain lifts out later this evening.
Later shifts can extend or cancel the advy as needed.

.LONG TERM...(Saturday night through Friday)
Issued at 350 PM EST FRI JAN 20 2017

Beginning Sat night/Sun, abundant low clouds will prevail across the
area and with precipitable water values in the .5-.6 range or 90 pct
above normal for late Jan climatology expect unusually high min
temps which will likely stay above freezing Sat night. If low clouds
dominate as they should, max temps Sunday won`t rise much from
the mins. Could certainly see only a few degree swing from Sat
night mins to Sun maxes, something like mins of 33/34 and maxes
near 38. A shortwave lifting n from the Plains and tracking mainly
w of the area, may generate some -ra on Sat evening. Otherwise,
expect some -dz at times thru the rest of the Sat night into Sun,
especially for locations favored in an upslope se flow.

A much more significant shortwave/low pres system will track
underneath the positive height anomaly in Canada, from the Gulf
Coast states Sat night to the se CONUS by Mon. While this system
will be much too far s and se of the area to bring pcpn, sfc/mid
level troughing extending back to the Upper Mississippi Valley
should help maintain some chc of -ra thru Mon. The best chc of rain
will be along and e of the sfc trough. The exact location of the sfc
trough is uncertain, but right now, it appears that it may cut nw to
se across Upper MI from the Keweenaw to northern Lake MI. Will
denote higher pops along and east of sfc trough axis. Cooling column
under height falls may support a mix with wet snow over the higher
terrain of the w.

Models indicate a more significant shortwave ejecting ne from the
western CONUS trough will reach the Great Lakes midweek. Continued
falling heights and cooling column will mean a ptype transition to
just snow, if not by Tue, certainly by Wed. The Canadian model
continues to be much more suppressed with the wave than the GFS, and
indicates the main synoptic pcpn shield staying well s of Upper MI.
The 12Z and 00Z ECMWF shifted a bit farther n, but not as far n as
the 12Z GFS. Both models would bring the synoptic snow shield into
Upper MI Tue night into Wed, though the GFS is more expansive
across the area than the ECMWF. GFS ensembles overall support the
operational GFS, but a number show an even farther n track. A good
number of the CMC ensembles are similar to the GFS track, just
delayed 12-24 hrs. So, it would seem there is a decent potential
for a period of widespread synoptic snow at some point Tue Night
into Wed/Wed night time frame with light to moderate les in nw
Lake Superior snowbelts behind the system into Thu, and then les
tapering off sometime on Fri as h85 thermal trough shifts east and
surface ridging moves in behind it. Whatever happens, the
positive tilt of the large scale trough in which the stronger
shortwave is embedded suggests that a wrapped up strong system is
unlikely. So, synoptic snow accumulations midweek should not be
significant, generally in the light to moderate range.

.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 551 PM EST FRI JAN 20 2017

Light rain will continue to lift across Upper Michigan this evening,
affecting all the TAF sites. Low cigs and low visibility in light
rain and fog will result in IFR to LIFR conditions into Sat. Upslope
flow will result in potential for VLIFR conditions at SAW and
possibly CMX. Could see conditions at both sites fall blo flight

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 310 PM EST FRI JAN 20 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.
Abundant low-level moisture will result in fog over northern Lk

Upper Michigan...
  Dense Fog Advisory from 10 PM EST /9 PM CST/ this evening to 1
     PM EST /noon CST/ Saturday for MIZ001-003>007-010-011-084-

  Dense Fog Advisory until 1 PM EST /noon CST/ Saturday for

Lake Superior...
Lake Michigan...
  Dense Fog Advisory until 1 PM EST Saturday for LMZ221-248-250.



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