Area Forecast Discussion
Issued by NWS Green Bay, WI

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000
FXUS63 KGRB 231120
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
520 AM CST Thu Feb 23 2017

Updated aviation portion for 12Z TAF issuance

.SHORT TERM...Today...Tonight...and Friday
Issued at 407 AM CST Thu Feb 23 2017

Short wave trough in a left front region of an upper jet let
which passed over northern Wisconsin overnight produced isolated
storms with small hail around midnight, then precipitation turned
to light snow then ended early this morning. DLH radar show some
weak returns approaching northern Wisconsin with ashland
indicating a mix. Will keep the light freezing drizzle mention
going this morning across the north.

Cooler but still above normal temperatures expected today in the
wake of a cold front overnight. Weak ridging passing over the area
today will provide a brief period of quiet weather.

Forecast issue then turns to the developing strong winter storm
system to impact the region starting later tonight and continuing
into saturday morning. Progs the last few days have been indicating
a dry slot working northward over eastern Wisconsin Friday and
keeping the deformation area with heavy snow mainly west of the
area. Trend and consensus of the latest progs suggests the dry
slot will be less of a feature, with only the 00z ECMWF hanging
onto this solution. Since this system is fragmented and stretched
out for long period of time, decided to deal with the system with
the primary events. Waa pcpn tonight into Friday and then the
system deformation snow tonight into Friday night.

Warm air advection precipitation is slightly slower tonight so
will start headlines around midnight for central and east central
Wisconsin and a few hours later for the north. Later shifts can
adjust time frame up if the waa band turns out to be faster.
Forecast soundings are indicating a mix of snow...sleet and
freezing rain before switching to mainly a rain mix over east
central Wisconsin. Total totals approaching 50 over east central
wisconsin Friday morning, so potential of convective type of
precipitation which could demand more than an advisory.
Precipitation type very challenging due to the warm ground at the
onset. Increasing northeast winds will usher in a cooling air mass
to aid with the mix.

The reason for the watch for central and north central Wisconsin
is due to the track of the 850 low. All models are persistent with
the 850 low tracking over east central Wisconsin later Friday
into Friday night while the surface low slides over southeast
Wisconsin. Not confident the waa pcpn will diminish enough over
central and north central Wisconsin so later shifts will need to
head to an advisory or warning. Even the advisory for eastern
Wisconsin is attempt to focus on the WAA precipitation late
tonight to noon Friday for the morning commute. Anticipate
additional headlines for that area if the waa band stalls over
northeast wisconsin and the deformation sets up eastward.

.LONG TERM...Friday Night Through Wednesday
Issued at 407 AM CST Thu Feb 23 2017

A 500mb low and a developing surface system are forecast to
approach the region from the western CONUS. The upper system will
be southwest of the area at 00Z Saturday with the surface low
over southern Lake Michigan. The locations of the upper system
and surface low were similar on the 00Z NAM/GFS/ECMWF, while the
Canadian was farther to the south. This system should bring
mostly snow to the forecast area as it tracks northeast to
Ontario by 12Z Saturday and Quebec by 00Z Sunday. Snow totals in
the forecast area on Friday night and Saturday are expected to be
no more than advisory criteria (<6" in 12 hours) based on a model
blend, but there will probably be some locally heavy totals.

Colder air moves in for the weekend behind the system as it
departs and there is a chance for some lake effect in the far
north. Temperatures should be a few degrees below normal before it
warms up toward the middle of the week. There are some chance PoPs
for Sunday as a mid level short wave passes and a weak surface low
tracks north of Wisconsin.

Surface high pressure should help to keep the forecast area dry
for a little while. Models are vastly different in their handling
of a system that is expected to impact the state starting Monday
night or Tuesday. At 00Z Wednesday the GFS showed a 1008mb
surface low in northeast South Dakota, the ECMWF had a 994mb low
in northeast Iowa, and the Canadian had a 989mb low between ASX
and IWD. This leads to very low confidence in the model blend of
toward the middle of next week. As it stands, there is a chance
for snow on Monday night, changing to rain on Tuesday, then
back to snow on Tuesday night. Wednesday has a mix of rain and
snow across the northwest half of the area and rain for the rest.
Stay tuned for changes to this part of the forecast.
&&

.AVIATION...for 12Z TAF Issuance
Issued at 520 AM CST Thu Feb 23 2017

Mainly MVFR cigs will linger this morning in the wake of a cold
front passage last night. Weak ridging into the state may improve
conditions to lower end VFR or higher end MVFR cigs this afternoon
and evening then deteriorate overnight as a strong winter storm
approaches the state. Northeast winds will turn blustery tonight
into Friday.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from midnight tonight to noon CST Friday
for WIZ031-037>040-045-048>050.

Winter Storm Watch from late tonight through late Friday night
for WIZ030-035-036.

Winter Storm Watch from late tonight through late Friday night
for WIZ005-010>012-018-019.

Winter Weather Advisory from 3 AM to 3 PM CST Friday for WIZ013-
020>022-073-074.
&&

$$

SHORT TERM.....TDH
LONG TERM......MG
AVIATION.......TDH



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