Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 232006
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
206 PM CST Fri Feb 23 2018

Forecast discussion for routine afternoon forecast issuance

.SHORT TERM...Tonight and Saturday
Issued at 205 PM CST Fri Feb 23 2018

Despite the passage of the low that brought us last nights
precipitation, low clouds remain across northeast Wisconsin this
afternoon. Model solutions differ on how to handle these low
clouds, as the MET would indicate the low clouds will hang around
for much of the night. However satellite observations do show some
drier air and clearing skies advecting in from the west along with
the more optimistic MAV forecast. The amount of clearing will have
an effect on overnight lows as more clouds would tend to keep
temperatures a bit warmer than MOS would indicate. Given satellite
trends will clear out skies a bit this evening and side with
cooler overnight lows ranging from 10 to 15 across the north, with
around 20 across the southeast.

Clouds will then increase again on Saturday as a low pressure
system lift northeast from the southern plains towards the mid
Mississippi Valley. The precipitation from this low is not
expected to start Saturday afternoon given the low level dry air
in place, therefore will keep POPs fairly low for the late
afternoon across the cwa. Highs Saturday will mainly be in the
30s.

.LONG TERM...Saturday Night Through Friday
Issued at 205 PM CST Fri Feb 23 2018

The combination of Pacific upper ridge and Gulf of Mexico to
western Atlantic upper high will continue to induce upper-level
troughing over the western CONUS through the end of next week.
Models then show some upper ridging to occur over the central
CONUS late in the week and turn the mean flow from southwest to
northwest. There will be two systems of interest (Saturday night/
Sunday morning and Wednesday night/Thursday night). Both systems
could bring a myriad of precipitation types (especially the first
system) which will be the main focus in the forecast. Temperatures
should be above normal through Wednesday, then slowly transition
closer to normal by next Friday.

The next late winter storm is forecast to quickly move northeast
across the region Saturday night and exit into southeast Ontario
on Sunday. The consensus model track takes the strong surface low
across central WI toward Lake Superior which would place eastern
WI in the warm sector Saturday evening before colder air begins to
wrap in behind the surface low later Saturday night. Anticipate a
mix of precipitation types in the evening ranging from snow north,
to rain south with a mix of rain/freezing rain/snow in between.
During the overnight hours, eastern WI would remain all rain,
while snow or a wintry mix to prevail over central/far northeast
WI. This system is stronger, more dynamic than its predecessor and
more headlines will be needed. Early indications are that most of
the forecast area would eventually be placed under a winter
weather advisory, however based on potential snow accumulations
approaching 6" across north-central WI, will issue a winter storm
watch from 03z Sunday to 15z Sunday for the counties of Lincoln,
Oneida and Vilas. Since the storm track can still waffle, prefer
to hold off on any advisories at this time. As far as ice
accumulation, potential looks to remain at 0.10" or less, mainly
over parts of northern and central WI. Min temperatures to range
from the middle 20s north-central WI, to the lower 30s eastern WI.
As the system departs on Sunday, there will be some lingering
light snow chances across northern WI during the morning hours.
Otherwise, drier air and blustery conditions to take over with
west winds gusting into the 30-40 mph range. Max temperatures to
range from the lower 30s north-central to the upper 30s eastern
WI.

A weak surface ridge axis slides into the western Great Lakes
Sunday night and allow skies to be mostly clear or become mostly
clear overnight. Min temperatures will be tricky depending on how
much new snow will have fallen and how fast winds can subside. May
need to tweak values down a bit over the north, otherwise look for
min temperatures to range from 10 to 15 degrees parts of north-
central WI, middle 20s east-central WI. AS the surface ridge
slides to our east on Monday, winds will become southwest and
start to tap some milder air. Models show a weak system moving
into southwest Ontario Monday afternoon, however all the lift/
forcing to remain well to our northwest, thus a dry Monday
expected. Under mainly mostly sunny skies, max temperatures to
range from the middle 30s north-central, lower to middle 40s
south.

Models differ a bit with regards to the timing/location of a weak
cold front into WI Monday night. The ECMWF blows the frontal
boundary through WI Monday night, while the GFS (and old GEM) do
not bring the front into parts of northeast WI until Tuesday
afternoon. The slower solution may allow enough moisture to arrive
to bring a chance of light rain to most of the area. For now,
since two models agree on this assumption, may add a small pop to
the forecast. Otherwise, Tuesday appears to be mostly cloudy with
max temperatures from the upper 30s north-central, middle 40s
south. Assuming the slower frontal timing is correct, this front
is progged to stall somewhere over far southern WI or northern IL
Tuesday night and we may need to carry a small pop across parts of
central/east-central WI. Attention then turns to the central/
southern Plains on Wednesday where another significant piece of
energy to eject out of the western upper trough. A surface low is
forecast to enter the southern Plains (although the GFS is quicker
with the lead surface low into MO by 00z Thursday). Prefer the
slower movement, especially with modest upper ridging over the
eastern Great Lakes. Thus, have kept Wednesday dry with max
temperatures in the middle to upper 30s north-central, lower to
middle 40s south.

Precipitation chances steadily increase Wednesday night through
Thursday as the system enters the Great Lakes region. Too early
yet for specifics, but this system looks colder than earlier
storms, thus the possibility of a more widespread snow. Anyone
with travel plans later Wednesday night or Thursday will want to
keep an eye on this system. Max temperatures are expected to begin
cooling on Thursday with readings in the middle 30s far north, to
around 40 degrees south. Snow chances would linger into Thursday
night and maybe into early Friday as the system is forecast to
slow down over the Great Lakes. Max temperatures Friday to range
from the lower 30s far north, to the upper 30s south.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1102 AM CST Fri Feb 23 2018

MVFR conditions will continue across the area during the afternoon
hours as an area of clearing and drier air works its way in from
the west. Although some model guidance suggests the low clouds
will remain through the overnight hours, the clearing out to the
west suggests otherwise, therefore will go with the more
optimistic forecast with this issuance and bring VFR conditions
to the TAF sites tonight. Some MVFR fog is possible later tonight,
then high clouds will stream in ahead of the next system
approaching from the west Saturday morning.
&&

.MARINE...
Issued at 205 PM CST Fri Feb 23 2018

A strong area of low pressure is forecast to move northeast into
Ontario on Sunday and will result in a short period of strong west
winds. Gales look possible for much of the day and will issue a
Gale Watch from 12z Sunday to 00z Monday.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Winter Storm Watch from Saturday evening through Sunday morning
for WIZ005-010-018.
&&

$$

SHORT TERM.....Kurimski
LONG TERM......Kallas
AVIATION.......Kurimski
MARINE.........Kallas



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