Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 092052

Area Forecast Discussion
National Weather Service Green Bay WI
252 PM CST Tue Jan 9 2018

Forecast discussion for routine afternoon forecast issuance

.SHORT TERM...Tonight and Wednesday
Issued at 252 PM CST Tue Jan 9 2018

Main focus is on freezing drizzle and fog potential, along with
cloud and temperature trends.

Mid-level clouds have persisted across most of the area this
afternoon. There is drier air noted south and west which will
continue to erode some of these clouds away late this afternoon.
Some locations, especially towards central Wisconsin, will
probably see a few clear hours before higher clouds start to move
in this evening.

Overnight, low level moisture starts advecting into the area.
Models are in agreement that this moisture is fairly shallow and
remains below 1km (925mb) tonight and Wednesday morning. This
combined with minimal lift limits the potential for freezing
drizzle. Kept a slight chance in the forecast from about 10Z to
16Z, but confidence of this occurring is not particularly high.
However, some slick spots are still possible since road
temperatures are expected to be below zero and we have a fairly
moist airmass riding over the snow pack. This could lead to some
frost formation on roads and sidewalks tomorrow morning,
especially over bridges and untreated roads.

Air and road temperatures will rise above freezing by midday which
will bring improvements to any slippery roads. The rest of the
afternoon is expected to be cloudy and mild with the potential for
fog formation as the boundary layer dew points continue to rise
into the 30s.

Temperatures will fall a little this evening then steadily rise
through tonight and Wednesday due to persistent WAA.

.LONG TERM...Wednesday Night Through Tuesday
Issued at 252 PM CST Tue Jan 9 2018

Precipitation type and amounts, and fog potential, Wednesday
night through Thursday evening are the main concerns during this
part of the long term. Forecast confidence is not high enough to
go with a watch or advisory with this issuance.

A surface low pressure system is forecast to drag a cold front
across part of the forecast area Wednesday night as a mid level
short wave trough approaches Wisconsin from the Panhandle region.
Increasing low level moisture ahead of the front will cause dew
points to rise into the middle 30s to around 40 degrees. Since the
ground is rather cold and/or snow-covered, fog is a pretty good
bet. Am concerned that the fog could be dense but at this point
only mentioned areas of fog. "Widespread" or "dense" wording may
need to be added as the event draws closer.

The 12Z models were slower with the progression of the cold front
than they were yesterday at this time. The slower solution would
lead to a slower and more messy change from rain to snow, with
less snow and more rain falling. The rather cold ground across far
northern Wisconsin could cause a layer of ice to develop there
before the changeover to snow. Based on the latest blend of the
models some locations in Vilas County could pickup more than 0.1
inch of ice. A change to mainly/all frozen precipitation is not
forecast to occur in the north until Thursday morning and not
until early evening in parts of east central Wisconsin. Models
had the highest QPF Thursday morning, with amounts decreasing
thereafter as the front passes across Wisconsin and the mid level
trough crosses the state. Snowfall totals should be highest in
Vilas County, where 2 to a little more than 4 inches of new snow
can be expected.

Once the upcoming system passes, colder than normal conditions
return as the upper flow transitions to an eastern trough-western
ridge pattern.

Due to the slow progression of the cold front, parts of north
central Wisconsin may experience falling temperatures throughout
the day on Thursday, while parts of east central Wisconsin will be
several degrees warmer than they are forecast to be on Wednesday.
Either way, highs on Friday may not even reach double digits in
the far north or 20 degrees in east central Wisconsin. Much below
normal temperatures are expected to persist through at least the
first half of next week. Highs are likely to be 10 to 15 degrees
below normal.

.AVIATION...for 18Z TAF Issuance
Issued at 1142 AM CST Tue Jan 9 2018

VFR conditions are expected to continue this afternoon and
evening. Current satellite imagery shows mid level clouds across
the area. Some drying to the west may produce some breaks in the
clouds at times, and then high clouds further to the west will
come in this evening. Less confidence in the forecast tonight and
Wednesday morning. As winds increase from the south moist air is
expected to flow in over the snowpack. This typically leads to
the development of low clouds and fog, and a changeover to
MVFR/IFR conditions, but timing the onset and strength is
difficult to pinpoint. Along with this is the potential for
freezing drizzle Wednesday morning, but again confidence is low.
IFR/LIFR conditions look more favorable beyond the current TAF
period into Wednesday night and Thursday.



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