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FXUS63 KGRB 091140

Area Forecast Discussion
National Weather Service Green Bay WI
540 AM CST Mon Dec 9 2019

Updated aviation portion for 12Z TAF issuance

.SHORT TERM...Today...Tonight...and Tuesday
Issued at 410 AM CST Mon Dec 9 2019

The main concerns for this portion of the forecast will be the 
potential for drizzle/freezing drizzle this morning along with 
widespread snow this afternoon. No major changes in the snowfall 
totals or headlines for today. Some slippery stretches are possible 
through the morning commute over the Fox Valley and along the Door 
Peninsula, but any slippery conditions should improved through mid 

Today: A surface low is expected to shift from northern MO/southern 
IA at 12Z to Lake Huron by 00Z Tuesday. As this happens, moisture is 
expected to deepen to the northwest of the surface low and near the 
850mb low. Forcing will also increase across all of the area as a 
coupled jet structure is expected to slide across the area 
throughout the day. Much of northeast WI will be on the southern 
fringes of the right-entrance region of a northern stream jet and 
the northern fringes of the left-exit region of the southern stream 
jet. Moisture is expected to deepen across the area throughout the 
day and cold air advection aloft will combine to increase the 
probability of ice crystal introduction into the cloud layer. This, 
in simple terms, will allow the drizzle/freezing drizzle to 
transition over to mainly snow throughout the day. The moisture in 
the DGZ is expected to become fairly deep across the central into 
north-central WI by this afternoon, allowing snow ratios to increase 
and snow intensity to increase. Farther east, across east-central 
and far northeast WI, it will likely take longer for the cold air 
and deeper moisture to transition the precipitation to all snow. 
Accumulations are expected to range from 3 to 5 inches across 
central and north-central locations to around 1 to 3 inches across 
the Fox Valley into far northeast WI, with the lowest totals 
expected along the lakeshore. Some minor flooding may occur along
the Bay as northeast winds increase through the morning hours, but
should not be as bad as the last couple events. High temperatures
will range from the 20s northwest to mid 30s southeast, with 
steadily dropping temperatures in the afternoon.

Tonight into Tuesday: As the low pressure system shifts from Lake 
Huron into Quebec, expect some wrap-around moisture to linger across 
eastern portions of the area into the early evening hours. Moisture 
will be deep enough across the area at that point to keep the 
precipitation in the form of light snow. Not expecting much more 
than an additional half inch or so across the Fox Valley into the 
Door Peninsula. Otherwise, with northwest to west-northwest flow, 
some light lake effect snow may push into northern Vilas County 
tonight into early Tuesday morning as 850mb temps drop to around -
20C to -24C. By late Tuesday morning into the afternoon hours, winds 
will shift far enough west to push the lake effect potential into 
Upper Michigan. Only minor accumulations are expected across 
northern Vilas County. Temperatures will be below normal for this 
time period with highs in the single digits to low teens above zero 
with overnight lows dropping into the single digits above and below 

.LONG TERM...Tuesday Night Through Sunday
Issued at 410 AM CST Mon Dec 9 2019

The largest impacts over the next week mainly revolve around the 
bitter cold Tuesday night into Thursday morning, followed by 
intermittent light snow chances thereafter.  

Tuesday night through Wednesday night...Arctic high pressure will be 
sliding southwest of the region on Tuesday night.  The coldest air 
of the season will be arriving by early Wednesday morning, with west 
winds of 5 to 10 mph creating wind chills of 15 to 25 below zero. 
Wind chills this low will likely lead to wind chill advisories for 
central and north-central WI.  Shortwave energy will be passing 
across the region on Wednesday morning.  Snow chances look to remain 
along and north of the U.P. border, as well as over southern 
WI/northern IL with this wave.  After a bitter cold day with highs 
only in the single digits above zero, arctic high pressure will 
become centered directly over the region on Wednesday night. 
Normally this setup would promote very cold low temps, but models 
continue to insist on mid and high clouds pushing in from the west. 
The may be a brief opportunity for temps to tank in the evening, and 
will trend towards colder guidance.

Rest of the forecast...The latest model runs are more aggressive 
generating light snow on Thursday in a weak warm advection regime 
with help from a shortwave impulse.  Thermal profiles are excellent 
for dendritic snow growth over far northern WI, which should support 
slightly higher snow totals over this area than further south and 
east.  But in the end, think amounts will be relatively light, maybe 
up to inch, possibly two on the high end.  Temperatures will be 
moderating Thursday into Friday, with readings warming into the 30s 
by Friday afternoon.  Shortwave energy will be moving across the 
area at times from Friday through the weekend.  Early indications 
suggest that Friday night into Saturday will offer the next best 
chance of widespread precip.

.AVIATION...for 12Z TAF Issuance
Issued at 540 AM CST Mon Dec 9 2019

Light freezing drizzle or drizzle along with some fog will
continue to impact the TAF sites this morning. Temperatures are
warm enough over the eastern TAF sites that the drizzle may not
freeze on surface, but a few slick spots are possible. Colder air
will work in from the west in the afternoon and transition the
drizzle/freezing drizzle to snow over the eastern TAF sites this
afternoon. Western TAF site, RHI, AUW and CWA will see the 
freezing drizzle transition to snow by mid to late morning and 
then continue through the afternoon hours. Snowfall accumulations
are expected to be in the 2 to 5 inch range over the western TAF
sites, while eastern sites will only see around an inch or two
this afternoon into this evening. Ceilings are already running in
the 300 - 600 ft range across the area with visibilities generally
running in the 1 to 3 mile range this morning. As the heavier snow
moves in during the day, visibilities will likely drop into the
1/2 to 1 mile range. Improving conditions can then be expected
tonight through the day Tuesday.

Winter Weather Advisory until 6 PM CST this evening for WIZ005-

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