Winter Storm Watch 8, NWS Green Bay, WI

Area Forecast Discussion
National Weather Service Green Bay WI
236 PM CST Tue Dec 25 2018

Forecast discussion for routine afternoon forecast issuance

.SYNOPSIS...
Issued at 235 PM CST Tue Dec 25 2018

Much more active weather than we've had recently. A major storm
system crossing the region will bring a round of mixed
precipitation Wednesday night into Friday evening, then some
light snow is possible at times during the weekend and into next
week.

A split flow regime with a dominant southern stream is evolving
across North America, as a deep upper trough develops over the
southwestern United States. Energy ejecting out of the trough
will drive a strong cyclone northeast through the Great Lakes
region the next several days. The models are struggling with the
evolution of the pattern thereafter, mainly due to uncertainty in
whether the southern stream or northern stream dominates next
week.

Temperatures will remain above normal for a couple more days, then
trend downward. How far downward will depend on whether the
northern or southern stream dominates. Given the moisture-rich
southern stream system affecting the area the next few days,
precipitation amounts will be above normal for the period.
&&

.SHORT TERM...Tonight and Wednesday
Issued at 235 PM CST Tue Dec 25 2018

This part of the forecast appears to be the relative calm before
the upcoming storm later in the week. Light snow that was falling
across parts of central and east-central Wisconsin this morning
exited the area by early this afternoon. There were still plenty
of clouds across the area as of 20Z. Do not expect clouds to clear
out as surface high pressure passes north of Wisconsin and
clouds, associated with a developing winter storm, move into the
area on Wednesday.

The clouds should keep temperatures from going into free-fall
tonight with little wind. Expect lows to range from the teens in
the far north to the mid 20s in east-central Wisconsin. Clouds
will also keep temperatures from rising a lot on Wednesday, so
highs will range from the mid 20s to mid 30s.

.LONG TERM...Wednesday Night Through Tuesday
Issued at 235 PM CST Tue Dec 25 2018

The primary emphasis for the long-term was attempting to discern
the precipitation type and snow amounts generated by the late-
week cyclone. Precipitation is expected to overspread the area
Wednesday night. Some concern that low-level dry air circulating
around the anticyclone departing to the east may delay the onset
of precipitation some--especially in east-central Wisconsin. But
considering the strong moisture transport above that, the delay
would probably just be a matter of hours and shouldn't
significantly impact the forecast. The dry air may slow warming
aloft due to some evaporational cooling, and produce a little more
snow over east-central Wisconsin before the changeover occurs.
Trended forecast in this direction, which lead to a little more
snow accumulation in east-central Wisconsin prior to the
changeover.

The large area of precipitation will continue to surge north
across the area late Wednesday night into Thursday, ahead of the
mid/upper level dry slot. Expect the dry slot will eventually
punch all the way through the area, stripping out middle and upper
level moisture and resulting in temperature/moisture profiles
unlikely to generate ice crystals. The main unknown is how much
snow falls prior to that happening. Totals over far north-central
Wisconsin looked close enough to warning criteria to justify
issuing a watch for Vilas county. That will help highlight the
situation at this point, with an advisory/warning decision
occurring in later forecasts.

Deeper moisture in the remnants of the comma head will swing back
across the area as the system begins to depart on Friday. The
system will be weakening by then, but a change back over to snow
and falling temperatures Friday afternoon into Friday evening may
result in another round of hazardous travel conditions.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1207 PM CST Tue Dec 25 2018

VFR conditions prevailed at most locations, but ceilings were MVFR
across the far south and southwest parts of the area at midday.
Expect some increase in ceiling heights across the south this
afternoon into the evening. After that, ceilings are forecast to
fall into the 1,000 to 2,000 foot range across the area later
tonight and remain that way through Wednesday morning. Any snow
should hold off until at least late Wednesday afternoon.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Winter Storm Watch from late Wednesday night through Thursday
afternoon for WIZ005.
&&

SYNOPSIS.......Skowronski
SHORT TERM.....MG
LONG TERM......Skowronski
AVIATION.......MG

Hazardous Weather Outlook
National Weather Service Green Bay WI
242 PM CST Tue Dec 25 2018

WIZ005-010>013-018>022-030-031-035>040-045-048>050-073-074-262045-
Vilas-Oneida-Forest-Florence-Northern Marinette County-Lincoln-
Langlade-Menominee-Northern Oconto County-Door-Marathon-Shawano-
Wood-Portage-Waupaca-Outagamie-Brown-Kewaunee-Waushara-Winnebago-
Calumet-Manitowoc-Southern Marinette County-
Southern Oconto County-
242 PM CST Tue Dec 25 2018

This Hazardous Weather Outlook is for north-central and northeast
Wisconsin.

.DAY ONE...Tonight

The probability for widespread hazardous weather is low.

.DAYS TWO THROUGH SEVEN...Wednesday through Tuesday

Hazardous travel is likely to develop across much of the area
Wednesday night, and continue Thursday across the north as snow
overspread the area. The snow will change to drizzle or light rain
from south to north late Wednesday night and Thursday.
Significant snow accumulations are possible across the far north.

The light rain or drizzle will change back to snow showers on
Friday and Friday evening, possibly resulting an another round of
hazardous travel conditions.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will not be needed tonight.

LMZ521-522-541>543-262045-
The Bay of Green Bay south of a line from Cedar River MI to Rock
Island Passage-Lake Michigan from Washington Island to Sheboygan-
242 PM CST Tue Dec 25 2018

This Hazardous Weather Outlook is for portions of northwest Lake
Michigan and the waters of Green Bay.

.DAY ONE...Tonight

The probability for widespread hazardous weather is low.

.DAYS TWO THROUGH SEVEN...Wednesday through Tuesday

Gale force gusts from the southeast are possible on the lake
Thursday into Thursday evening.

MG/Skowronski