Area Forecast Discussion
Issued by NWS Green Bay, WI

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

FXUS63 KGRB 132329

Area Forecast Discussion
National Weather Service Green Bay WI
529 PM CST Wed Dec 13 2017

Updated aviation portion for 00Z TAF issuance
and new information added to update section

Issued at 523 PM CST Wed Dec 13 2017

Will Extend the southern Marinette/Oconto and Brown county
warnings to 03Z to match the lakeshore. Snow will be ending, but
it is very windy near the lake and bay, so travel will be very
slow to improve. Will also extend the advisory for the Fox Valley
and areas just to the NW. The remainder of the advisory will be
allowed to expire at 600 pm as scheduled. Coding is as shown

The HRRR indicates a lake band will still be over Manitowoc
County at 03Z, so we may need to revisit the expiration time there
later this evening. But there is always uncertainty in the
location of lake bands, so we`ll see how things evolve before
making any decisions on extending there.

Issued at 433 PM CST Wed Dec 13 2017

Some headline decisions will need to be made soon. Have not
reached any final decisions yet, but feeling is that the warning
for Brown and the advisory for the rest of the Fox Valley will
need to go past scheduled expiration at 600 pm. Conditions look
like they will probably ease enough to allow the advisory for
central/north-central Wisconsin to expire as scheduled. The
Oconto/Marinette county area may the toughest call. Looks like a
bit more of a lake/bay influence there now with some transverse
banding on the radar. That`s dropping south, but still 1/2SM vsby
on the Washington Island AWOS. Winds are strong in this area too.
Looking to have final decision on headline changes by 530 pm.

Issued at 342 PM CST Wed Dec 13 2017

Travel conditions, which weren`t very good to begin with, are
likely to become very difficult in east-central Wisconsin for the
next couple hours.

A small-scale frontal boundary extends from near KPCZ to KATW to
KSBM. Increasing northeast winds north of the boundary were
meeting more northerly/northwesterly flow on the other side of
the boundary, leading to strong convergence near the frontal zone.
Radar returns northeast of the boundary have been increasing, and
local mesoplots showed a significant deepening of the dendritic
growth zone across the area. The result should be a period of
heavy or very heavy snowfall, with rates AOA 1 inch per hour.

In addition, winds above the surface were increasing and backing,
and will come through 040 in the 925-850 mb layer in the next few
hours. That will likely lead to some gusts over 30 mph near Green
Bay and along the lakeshore. Near whiteout conditions with very
low visibilities are likely at times.

Already sent an SPS highlighting the short-term situation, and a
graphical Wx story is on the way. Will be updating the WSW next to
adjust snowfall wording.

.SHORT TERM...Tonight and Thursday
Issued at 251 PM CST Wed Dec 13 2017

The latest RAP analysis and satellite/radar imagery show low
pressure moving into north-central WI early this afternoon. The
coldest cloud tops and heaviest snowfall rates are occurring over
northeast WI where visibilities are down to 1/4sm at times. East
winds are increasing along the Bay and Lake with gusts to 35
mph. As snow continues to pile up over northeast WI and winds
shift to the northeast, expect blowing and drifting snow to impact
areas into the Fox Valley this afternoon. Added Manitowoc County
to the warning, given a report of 5 inches so far at Mishicot and
winds gusting up to 30 kts on the lakeshore. No additional changes
expected as the snow and snow/blowing snow should keep roadways
in poor shape through the evening commute. The worst conditions
should occur over far northeast WI. Snow/wind trends are the main
forecast concern.

Tonight...Low pressure will continue to move southeast towards
northern Ohio this evening. Hi-res models indicate that snow will
be ending over northeast WI by mid-evening. Winds will remain
gusty through midnight over eastern WI though, so roads may will
likely be slow to improve. Additional accums are projected to be
less than an inch this evening, highest over the lakeshore areas.
Models then insist on rapid clearing taking place from the north
behind the system, particularly for central and east-central WI
overnight. But with winds onshore from Lake Superior there is
potential for clouds to remain broken for the entire night. Lows
ranging from the mid single digits to mid teens.

Thursday...The next clipper will pass across the region, though it
will be considerably weaker and have less moisture to work with
than todays potent system. Still though, should see clouds
increase again in locations which saw clearing tonight. In
addition, moisture looks deep enough for flurries and light snow
showers from mid morning over central WI and midday over eastern
WI to the end of the afternoon. Some areas could see a dusting.
Seasonable with highs ranging from the upper teens to mid 20s.

.LONG TERM...Thursday Night Through Wednesday
Issued at 251 PM CST Wed Dec 13 2017

A weak upper level disturbance will track across the area Thursday
night into Friday, bringing snow showers and flurries to much of
the area, but accumulations will be under a half inch for all but
far north central WI where an inch or two is possible as some lake
effect/enhancement from Lake Superior is expected. Friday looks to
be the coldest day in the period, with highs struggling to get
into the teens in the Northwoods and into the lower 20s in the Fox

The chance for flurries or snow showers will continue Friday night
into Saturday, especially across northern WI, as another
shortwave rotates along the western edge of a upper low sitting
over northeast Ontario. Most persistent and heaviest activity will
remain over north central WI as Lake Superior continues to aid in
the snow shower development. Some dry air will get into the mid-
levels on Saturday, leading to the chance of some freezing
drizzle, but confidence not high enough that precip will actually
occur to add to the forecast. Friday night looks to be the
coldest night in the period, with lows below zero possible across
north central WI and single digits above zero across the rest of
the area, away from Lake Michigan.

Models bring another shortwave into the area this weekend, now
focusing more on Sunday, but model differences are significant,
especially between the GEM/ECMWF and the GFS. Models handle both
the system crossing the northern Plains and another system
tracking NE from the southern Plains. The interaction of these two
systems will determine what, if any, precip chances will occur
this weekend into early next week. Temperatures look to return
closer to normal on Saturday, then slightly above normal Sunday
into early next week as the flow turns more W/SW.

.AVIATION...for 00Z TAF Issuance
Issued at 523 PM CST Wed Dec 13 2017

Meteorological conditions will improve as the storm system exits
the area. But winds will remain strong over east-central
Wisconsin, so drifting snow will likely continue to be a
consideration for airport operations for the rest of the night.

Winter Weather Advisory until 9 PM CST this evening for WIZ020-

Winter Storm Warning until 9 PM CST this evening for WIZ022-039-

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


LONG TERM......Bersch
AVIATION.......Skowronski is the U.S. government's official web portal to all federal, state and local government web resources and services.