Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 222351

Area Forecast Discussion
National Weather Service Marquette MI
651 PM EST Sun Jan 22 2017

Issued at 650 PM EST SUN JAN 22 2017

With lots of lingering llvl mstr/near zero sfc dewpt depressions
over melting sn pack and under light winds and mid lvl dry air,
area obs/webcams show some dense fog is dvlpg. Even though some hi
clds may impact mainly the w half of the cwa tngt, expect
conditions for dense fog to remain fvrbl. So issued a dense fog
advy into late Mon mrng for the entire cwa.

.SHORT TERM...(This evening through Monday)
Issued at 257 PM EST SUN JAN 22 2017

Sheared out shortwave over Upper Michigan and Lake Superior along
with sfc low over northern Lk Superior has brought isold light rain
showers and drizzle to a few areas of cwa today. Otherwise, the low
clouds and fog continue. The fog is not as widespread as it was this
time 24 hr ago possibly due to weak westerly flow on southern edge
of the low. Some areas do continue to see dense fog with much of
Keweenaw seeing vsby 1/4sm much of day and also over eastern U.P.
Shortwave trough weak as it is could still keep some light showers
or drizzle going tonight especially across the east cwa. Only light
precip expected but with temps falling to the lower 30s, there could
be some icy spots on untreated roads, sidewalks and parking lots. As
for the fog plan for areas of dense fog but not sure if it will be
as widespread as last night. Winds will be light but visible
satellite shows scattered to broken high clouds upstream which could
move across and disrupt radiational cooling potential at top of low
cloud deck in place. Issued a Special Weather Statement highlighting
areas of dense fog and possible black ice due to lingering moisture
and drizzle. Did not issue dense fog advy though based on concerns
of how widespread dense fog tonight will be. Later shifts can issue
if needed.

On Mon, shortwave over central Plains lifts toward the region. Rain
could become more widespread over eastern cwa as the forcing arrives
and since that area is in area of greater moisture aloft h7-h5.
Elsewhere drizzle would be the main ptype and best chance of that
would be near Lk Superior as winds become more northerly through the
day. Fog will gradually diminish but could hang on into the aftn
over the north closer to Lk Superior with onshore upslope flow (as
is occurring today over the Keweenaw Peninsula).

.LONG TERM...(Monday night through Sunday)
Issued at 357 PM EST SUN JAN 22 2017

Beginning Monday night...Shortwave lifting ne through Upper Mi and
associated modest forcing/q-vector convergence out ahead of it could
support some light precipitation over mainly the eastern portion of
the cwa, east of the inverted sfc trough hanging over the area.
Model forecast soundings would support a p-type of a snow/rain/sleet
mix in the evening east changing over to mainly light snow late.
Shallow moisture well blo height of -10C isotherm as depicted by
model soundings will likely only support light dz/fzdz across much
of the western/central counties. Could be some formation of patchy
fog as well, aided by daytime melting on Monday. Consensus of model
guidance suggest min temps around 30F.

Tuesday...After some lingering morning snow showers east from
shortwave departing the area Mon, expect most of Tuesday to be dry
as weak ridging moves in behind the shortwave. Looks like clouds and
possibly fog (dew points still in the lower 30s) will remain over
the area though as low-level moisture remains trapped under mid-
level subsidence.

Models indicate a more significant shortwave ejecting ne from the
base of a broad western CONUS trough will reach the Great Lakes
midweek. Continued falling heights and cooling column will ensure
ptype of just snow, by Tue night/Wed. The 12z GFS remains slightly
quicker and farther north than the 00z ECMWF. The 12z GFS takes a
track across the Mackinac Straits midday Wed while the 00z ECMWF
tracks the sfc low just south of the thumb in Lower Mi Wed
afternoon. Most GFS ensemble members would support a track across
central Lower Mi to the thumb more in line with the 12z ECMWF.
Meanwhile, the 00z Canadian remains much slower and farther south
than any of the models with the sfc low tracking through
central/northern IL Wed afternoon.  The Canadian ensemble mean for
sfc low is a bit farther north than 00Z run (with a track through
far southern Lower Mi) and about 12 hours quicker. Expect better
data sampling of this shortwave for model input by Mon night once
the shortwave moves onshore near the Baja of California.

In any event, following a favored blend of GFS ensemble and the
00/12z ECMWF it would seem there is a decent potential for a period
of widespread synoptic snow at some point Tue night into Wed time
frame. Models indicate a positive tilt of the large scale trough in
which the stronger shortwave is embedded which would suggest that a
wrapped up strong sfc low is unlikely. So, would expect synoptic
snow accumulations be generally be in the light to moderate range,
likely heaviest south and east. Expect light to possibly moderate
les in the nw Lake Superior snowbelts behind the system Wed night
into Thu as h85 temps drop from around -6C 00z Thu to around -10C.

Fri-Sun...Models indicate pattern amplification taking place with
amplifying ridge over western North America and resulting broad
downstream trough across much of the eastern half of North America.
This will allow a series of clipper shortwaves to move across the
Upper Great Lakes providing reinforcing shots of colder air (h85
temps around -13 Fri morning will lower to around -18c by Sunday)
with temps trending closer to normal through next weekend. Also the
increasingly colder air and subsequent instability over Lake
Superior will generate more les for the nw wind snowbelts
through next weekend with moderate snow accumulation possible.

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 624 PM EST SUN JAN 22 2017

With lingering llvl mstr over melting sn pack and light winds,
expect some dense fog with LIFR/VLIFR conditions to predominate
until mid/late Mon mrng. While there is likely to be improvement in
vsby on Mon into perhaps the MVFR category, lo cigs in the LIFR to
IFR range wl linger.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 257 PM EST SUN JAN 22 2017

A relatively weak pressure gradient over the Upper Great Lakes in
the absence of any strong weather systems will continue to result in
winds under 20 kts over Lake Superior most of the time into Mon and
Tue. Expect N to NW winds to 25 kts late Wed through the end of the
week as low pressure over the central Plains moves toward eastern
Canada and colder air returns to the Lk Superior region.

Upper Michigan...
  Dense Fog Advisory until noon EST /11 AM CST/ Monday for

Lake Superior...
Lake Michigan...
  Dense Fog Advisory until 1 PM EST Monday for LMZ248-250.



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