Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 141717

Area Forecast Discussion
National Weather Service Green Bay WI
1117 AM CST Sat Jan 14 2017

Updated aviation portion for 18Z TAF issuance

Issued at 324 AM CST Sat Jan 14 2017

Still cold today and tonight, then a significant warming trend.
A round of mixed precipitation is likely early next week.

The upper flow across North America will become split during the
period as a strong negative upper height anomaly evolves along
the west coast and a positive anomaly develops over eastern
Canada. The split will cut off the direct feed of arctic air into
the area, so after a cold start to the period temperatures will
warm to significantly above normal. Significant precipitation will
occur if and when southern stream systems affect the area. One
such system will cross the region during the early part of the
work week. The system will tap gulf moisture, so precipitation
amounts will probably end up above normal for the period.

.SHORT TERM...Today...Tonight...and Sunday
Issued at 324 AM CST Sat Jan 14 2017

Tranquil, especially compared to what occurred during the middle
to latter part of the past work week and what is likely to happen
early next week. A large anticyclone will remain sprawled across
the Great Lakes region, beneath strong upper confluent zone. Low
clouds across the area this morning will dissipate as they shift
east, making timing of the clearing a bit of a challenge. Upper
flow tilts a little northwest also, which will probably drive the
cirrus shield south of the area.

Although the air mass across the area has moderated some since it
first arrived from Canada, clear skies tonight will still allow
for a large fall in temperatures. The primary area of concern is
far north-central Wisconsin, which will be on the edge of a
stronger surface pressure gradient. Winds will be critical to
temperatures. Opted to go near or below the cold end of the
guidance envelope, though held back a little in the north due to
the uncertainty in winds dying off completely. Under sunny skies,
temperatures will continue their rebound on Sunday.

.LONG TERM...Sunday Night Through Friday
Issued at 324 AM CST Sat Jan 14 2017

Main concern for this period will be wintry mix overspreading the
region on Monday and continuing into Tuesday before changing to
rain at most places. The biggest change to the forecast was to
add a little more snow across the far north as the 00z ECMWF has
trended cooler with the warm layer in this region. Still will be a
mix across this region. The other change was to keep the
precipitation out of the area until after 6 am on Monday.

For the remainder of the area, precipitation will start out as
snow, transition to sleet and freezing rain before changing to
rain. A quick look at pavement surfaces indicated the sub surface
temperatures was mainly in the middle to upper 20s. This would
mean pavement temperatures will be slow to respond despite
temperatures being at least a few or several degrees above
freezing. This is the most difficult portion of the forecast is
trying to figure out when the pavement temperature will rise far
enough above freezing to offset the cooling from below (sub-
surface temperatures). From previous experience, you will need at
least a few to several hours above freezing to get the pavement
temperatures above freezing during the day. It becomes more
complicated at night due to the loss of solar radiation and
cooling from below. In other words, hazardous travel is expected
to develop across central and northeast Wisconsin Monday morning
and then spread northward into north-central and far northeast
Wisconsin Monday afternoon and evening.

At this time, ice amounts around a tenth of an inch or less is
expected from the Fox Valley and lakeshore region. This is
assuming surface temperatures remain several degrees above
freezing Monday night. Expecting this will occur due to easterly
flow off the warmer waters of Lake Michigan. For locations just
north and west of the Fox Valley, air and road temperatures do not
respond as quickly as the lakeshore and Fox Valley, thus expecting
a more prolong period of freezing rain. Ice accumulations of 0.10
inch to 0.25 inches is anticipated at this time. The precipitation
should change over to all rain north and west of the Fox Valley
late Monday night or more than likely Tuesday morning. Freezing
rain will still be possible across the far north Tuesday
afternoon, mainly due to the cold roads.

There is a small chance of precipitation Tuesday evening, with
another chance of rain showers next Friday. The big story next
week will the mild temperatures with highs in the 30s and 40s.

.AVIATION...for 18Z TAF Issuance
Issued at 1117 AM CST Sat Jan 14 2017

Last of persistent IFR cigs to exit east-central WI early this
afternoon, leaving VFR conditions to prevail for the rest of the
afternoon into tonight. There may be some patchy ground fog across
central WI late tonight which could lower vsbys into the MVFR
range, but this appears to be spotty at best. Otherwise, a broad
area of high pressure over the Great Lakes will keep the weather
dry with relatively light winds through Sunday.

The early part of next week will be a different story as a system
brings a potential wintry mix of precipitation to northeast WI
from Monday afternoon into Tuesday night.



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