Area Forecast Discussion
Issued by NWS Green Bay, WI

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000
FXUS63 KGRB 271722
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1122 AM CST Fri Jan 27 2023

Updated aviation portion for 18Z TAF issuance

.SYNOPSIS...
Issued at 425 AM CST Fri Jan 27 2023

Windy with a round of snow across the area today, with another
possible across mainly central and east-central Wisconsin Saturday
into Saturday evening. Mild this afternoon, then much colder for
the weekend.

High amplitude large scale flow was now in place across North
America, anchored by a strong longwave ridge just off the west
coast. The downstream trough will initially be along 80W, then
re-orient into a more positive tilt from northern Hudson Bay to
the Desert Southwest early next week. By that point, the western
ridge will be start to be flattened by Pacific energy. The
downstream flow will react by splitting into a strong northern
stream with continued troughing over Hudson Bay, and a weaker,
progressive southern stream across about the southern half of the
CONUS.

It will feel rather chilly this morning due to increasing south
winds and snow, but afternoon readings will warm to considerably
above normal as winds shift west. Much colder weather is expected
for the weekend, with below normal temperatures continuing
through at least the middle of next week. The pattern will support
periodic light snow events early in the period, then drier
weather during the latter half of the period. The 7 day total will
probably end up below normal.
&&

.SHORT TERM...Today...Tonight...and Saturday
Issued at 425 AM CST Fri Jan 27 2023

A strong cyclone will track from northwest Minnesota this morning
to just northeast of Lake Superior by late today. Modest QG
forcing with the attendant shortwave combined with isentropic lift
with the LLJ will act upon an atmosphere with fairly steep (7-7.5
K/km) mid-level lapse rates to generate a band of snow that will
sweep east through the area. Despite being in the very near term,
models seemed to be struggling with timing. In addition, some
flurries were developing out of the expanding low-deck ahead of
the main snow band. The local mesoanalysis low-level saturation
plot showed a rapid eastward progression of moisture due to strong
SSW flow in the 925-850 mb layer. As a result, anticipate snow to
increase in intensity fairly quickly after the arrival of the
main band. This will probably result in rapidly deteriorating
travel conditions, and will highlight the situation with an SPS.

The main snow band should push through fairly rapidly during the
morning, bringing an inch or two of snow to most locations.
Scattered snow showers will linger in the wake of the band. The
warm front oriented south of the cyclone will push east through
the area during the mid-day hours. The air behind the front
downsloped the Rockies and was quite warm (4 am temps in the mid
30S across far ern SE and SW MN), so pushed highs above guidance--
especially across the srn part of the area. Westerly winds gusting
to around 30 mph will produce some blowing and drifting of the
snow until temps warm to freezing.

The cold front trailing from the cyclone will cross the area
during the evening, ushering in a much colder air mass. Overnight
temperatures are again tricky. As was the case in the forecast
for this morning, there is great uncertainty in skycon and whether
or not clear skies will overlap a period of light winds. Stayed
close to a broad-based blend of guidance products.

A low amplitude mid-level shortwave progressing east from the
Plains will generate a wave on the slowing/stalling frontal system
to our south on Saturday. The overall trend on the guidance has
been to track the system farther north with time. The 00Z GFS was
one of the last of the models to keep precip from the system south
of the area, but the recently arrived 06Z run took a jog north.
Timing is an issue as the UKMET and GFS suggest the bulk of the
precip will occur in the 00Z-06Z time frame while most of the
other models are quicker. Will start by raising PoPs across about
the southern half of the area during the afternoon. One lingering
item of concern is that the mid-level FGEN on the models seems
displaced a little farther north than typical compared to the
upper level jet crossing the region. That doesn`t necessarily mean
it could not occur as progged, but it is something worth
following in later model runs.

.LONG TERM...Saturday Night Through Thursday
Issued at 425 AM CST Fri Jan 27 2023

The main forecast concerns from this forecast period revolve around
the potential for light snow accumulations Saturday night into
Sunday, and the arrival of a much colder airmass.

Saturday night through Sunday...As a low pressure system lifts
northeast across northern IL to the eastern Great lakes by Sunday
morning, central and southern WI will be under the influence of the
system`s f-gen band Saturday night through early Sunday morning. As
a result, accumulating snow will continue across portions of central
and east-central WI through early Sunday morning. There is still
some uncertainty with how far north the axis of highest snowfall
will lift, but models continue to suggest it will remain across
southern WI. For Saturday night through Sunday morning, additional
snowfall for central and east-central WI of a dusting to an inch is
possible, with the highest amounts in the extreme southeastern
portion of the forecast area. The remainder of Sunday will be dry
and colder as a surface high pressure system shifts into the Upper
Mississippi Valley.

Rest of the extended...Some model guidance is suggesting an area of
light snow quickly moving across the region late Sunday into early
Monday, but there appears to be a disagreement with the amount of
mid-level moisture. As confidence is not high with this feature,
have only included slight chance PoPs during this time period. Aside
from this feature, dry and much colder conditions are expected for
the remainder of the extended, with the potential for wind chill
headlines. The core of the coldest air will be over the region on
Monday, with single digit high temperatures and afternoon wind
chills below zero. Very cold conditions are then anticipated for
Monday night with lows ranging from -15F to -2F degrees, and wind
chills of at least -20 at most locations, which meets Wind Chill
Advisory criteria. The cold air will stick around through the
remainder of the work week, but there are signs of some warming at
the end of next week with the possible return of highs in the 20s.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1108 AM CST Fri Jan 27 2023

A band of snow across the area during the morning should diminish
and then end from west to east this afternoon. The only exception
will be across the far north where lake effect snow showers or
flurries will linger into tonight. Gusty south/southwest winds
will veer to the west this afternoon. Most places will see gusts
of 20 to 30 kts. The gusty winds could create some areas of
blowing and drifting snow into early this evening. Winds will
gradually subside this evening. Northwest winds are expected to
veer to the northeast on Saturday. For Saturday, a system passing
to the south will bring another chance of snow to central and
east-central Wisconsin late Saturday morning into Saturday night.
There are still some issues on how far north the snow will make it
into northern Wisconsin. The 00Z TAFS will reflect current
thinking on how far north the snow will make it into the area
since most of it would occur Saturday afternoon and evening.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

SYNOPSIS.......Skowronski
SHORT TERM.....Skowronski
LONG TERM......Kruk
AVIATION.......Eckberg


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