Area Forecast Discussion
Issued by NWS Green Bay, WI

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000
FXUS63 KGRB 230014
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
614 PM CST Wed Feb 22 2017

Updated aviation portion for 00Z TAF issuance

.SHORT TERM...Tonight and Thursday
Issued at 351 PM CST Wed Feb 22 2017

After a record setting temperature day across much of the area,
major changes are on the way. Forecast challenges in the short
term will mainly be precip trends tonight.

Light rain showers and sprinkles will spread across the area late
this afternoon and early evening as a weak surface low pressure
system pushes across the area, moisture increases in the low and
mid levels and a cold front sagging north to south through the
night. The most widespread activity will actually be later this
evening as a compact shortwave crosses Upper Michigan, but most of
this activity will be near or north of the Michigan border. There
could even be some thunder with this shortwave. Temps look to get
cold enough overnight for the rain to mix with or change over to
snow over far northern WI. Also, as the front drops south, we
start to lose ice crystals in the clouds, so some freezing drizzle
is possible after midnight across north central WI.

Other than some lingering freezing drizzle over far north central
WI, dry weather is expected during the day as weak / short-lived
ridge moves across the state. Light rain will approach central WI
by late afternoon as the significant weather system approaches
from the southwest. Temperatures will be much cooler than today,
as 850mb temps drop 7-10C, but highs will remain well above
normal for this time of year.

.LONG TERM...Thursday Night Through Wednesday
Issued at 351 PM CST Wed Feb 22 2017

A strong upper ridge in the eastern Pacific will dictate the
weather across the CONUS into next week as a series of systems
top the ridge, drop south into the western CONUS, then sweep
northeast across the central/northeast CONUS. There are two
systems of interest (Thu night-Sat) and (Tue-Wed) that need to be
dealt with. Main forecast focus to be on system #1 as storm track
is still uncertain, which leads to precipitation type and snow
accumulation issues. Temperatures are expected to settle closer to
normal on average with Saturday looking like the coldest day.

Even though the system to still be located over the central
Plains/Midwest Thursday night, a surge of gulf moisture,
isentropic lift, frontogenetical forcing and a hint of a coupled
jet structure will bring a swath of precipitation into WI from
late evening through the overnight hours. For the most part,
precipitation type would be all snow, except for a potential
rain/snow mix south of a Wautoma-Manitowoc line as warmer air
lifts northward. Snow accumulations by daybreak would mainly be in
the 1-3" range. In addition to the precipitation, winds will
become gusty later Thursday night, pushing 30 mph by daybreak.

Models remain inconsistent with the eventual track of the surface
low headed into Friday. This run-to-run waffling, coupled with the
unknown strength/location of a dry slot, place confidence a little
lower than I would like at this stage (under 48 hours). The 12z
model output are now tracking a little farther south than
yesterday with the dry slot arriving Friday afternoon. The surge
of warmer air ahead of the surface low (expected to reach
southwest WI/northwest IL by 00z Saturday) will limit 1+" of snow
to northern WI Friday morning. If the dry slot materializes as
expected, we would be looking at drizzle or freezing drizzle over
northeast WI. Therefore, due to the uncertainty involved, have
held off on any headlines and will issue a SPS.

As the surface low continues to track northeast into Lower MI
Friday night, colder air will gradually get pulled into the
forecast area with any rain mixing with and eventually changing to
all snow. The main mid-level trough will also be over the western
Great Lakes to add some mid-level forcing. Additional snow amounts
will be a few tenths of an inch eastern WI, 1-3" over central WI.
Light snow will continue into Saturday morning as northeast WI
gets under the cyclonic side of the departed mid-level trough.
Another 1-2" of snow will be possible Saturday morning before the
snow diminishes Saturday afternoon. Colder air to have overspread
the region by Saturday with max temperatures only in the lower 20s
north-central, upper 20s east-central WI.

A weak surface ridge moves across WI Saturday night, at least
providing for a brief break in the precipitation chances. Small
snow chances return on Sunday as a weak cold front pushes into WI.
Not much QPF evident, thus any snow would be light. Another
surface high moves across the Great Lakes Sunday night into
Monday, bringing dry conditions with temperatures close to
seasonal normals.

System #2 is progged to begin affecting our weather Tuesday
afternoon through next Wednesday. Storm track will again be a big
factor for precipitation type, but it is too early to determine
where the rain/snow line will set up. This system will need to be
watched in the coming days.
&&

.AVIATION...for 00Z TAF Issuance
Issued at 614 PM CST Wed Feb 22 2017

A cold front moved across the area during the afternoon hours. It
will be followed by some scattered light showers this evening, and
MVFR ceilings later tonight. The clouds will likely scatter out by
Thursday afternoon. A winter storm will bring IFR conditions and a
mix of snow, sleet, freezing rain and rain Thursday night through
Saturday.
&&

.MARINE...
Issued at 351 PM CST Wed Feb 22 2017

A strong area of low pressure is forecast to impact the region
from Thursday night through Saturday. Northeast winds ahead of the
low, followed by northwest winds behind the low, could gust to
gale force. A gale watch has been issued from 06z Friday to 21z
Friday.
&&

.HYDROLOGY...
Issued at 351 PM CST Wed Feb 22 2017

Rivers across central WI will continue to fall tonight, while slow
rises will continue in the Wolf/Little Wolf/Menominee river
basins. Additional flood concerns are possible Thursday night into
the weekend as up to another inch of water is expected, however,
how much runoff occurs will be depending on precipitation type.
Minor ice jamming is also possible across northern WI, especially
in the Menominee river basin.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM.....Bersch
LONG TERM......Kallas
AVIATION.......RDM
MARINE.........Kallas
HYDROLOGY......Bersch



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