Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 010456
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1056 PM CST Tue Feb 28 2017

Updated aviation portion for 06Z TAF issuance

.SHORT TERM...Tonight and Wednesday
Issued at 240 PM CST Tue Feb 28 2017

The latest rap analysis and satellite/radar imagery show an area of
low pressure moving east-northeast over Iowa and a warm front
extending east across southern Wisconsin.  Showers and thunderstorms
developed north of the warm front earlier today and grazed east-
central WI.  These storms have passed on to the east. Very little
precipitation upstream, though some light precip is trying to get
going over northeast Iowa. Meanwhile, a cold front is dropping
southeast over far northwest Wisconsin and is producing a band of
light rain.  This band may just clip Vilas county later this
afternoon.  Fog also been an issue today, with visibilities dropping
to a quarter mile or less at times.  Looking at area webcams, the
fog does not appear to be that hazardous though, so will continue to
provide updates using the sps.  Finally the next storm system is
moving across the Rockies.  Complicated weather will impact the
region through Wednesday, and forecast concerns revolve around fog
through this evening, then snowfall potential late tonight into
Wednesday.

Tonight...A shortwave trough will intensify as it moves across the
Plains while a wave of low pressure travels northeast along the cold
front across northern Illinois and lower Michigan.  The strongest
forcing this evening will reside south of our area closer to the
wave of low pressure, but upper divergence will remain overhead
which will keep a chance of light precipitation in the forecast.
Think chances of precipitation will improve overnight as the
shortwave from the Plains draws closer and mid-level fgen increases.

Northeast to north winds will gradually draw in colder air through
the night, with any precip gradually changing over from a rain snow
mix or all rain over to snow from northwest to southeast.  Minor
accumulations are possible by daybreak mainly west of the lakeshore.
In terms of dense fog, should see improvements with the visibilities
as northerly winds strengthen and draw in colder/drier air this
evening.  Will keep a mention of dense fog through midnight across
across the east.

Wednesday...The snowfall is expected to intensify early in the
morning as the deformation zone of a potent shortwave slides into
the state.  With ample moisture and lift, numerical models have
increased precip over parts of central and most of eastern Wisconsin
for the morning before precip exits by late in the afternoon.  Of
particular concern is the possibility of intensifying snows during
the morning commute.  Snows should peak from about mid-morning
through early afternoon before trailing off from northwest to
southeast.  Increased snow amounts into the 3-5 inch range south of
a line from Marshfield to the tip of the Door, which places this
area solidly into the advisory range.  Some blowing and drifting is
possible west of the Fox Valley and Bayshore where where snowfall
will be more of a normal type of snow, but the snow should be more
of a heavy variety over eastern WI, which should limit the blowing
and drifting.  Temps will remain relatively steady and range from
the lower 20s north to near 30 in the south.

.LONG TERM...Wednesday Night Through Tuesday
Issued at 240 PM CST Tue Feb 28 2017

Active weather leaves the region Wednesday night into Thursday
morning with predominantly northwesterly flow. A couple of shortwaves
will ride through the region ahead of an upper level ridge, which
could bring in a chance for some snow showers Thursday night and
Friday morning. Models differ on the overall chances as the GFS
and NAM bring in a brief round of snow showers and the ECMWF
remains drier. Differences primarily seem to stem from the amount
of available moisture and the amount of dry air at low levels, so
lower pops were preferred through the period with only trace to
minor accumulations of snow across the area.

The upper level ridge will then keep the area drier through most of
Friday and Saturday. The only brief chance of snow showers arrives
Friday night as another weak shortwave, coupled with low to mid
level warm air advection, moves through the region on the backside
of the ridge. Snow chances will remain slight once again, as
models differ on the amount of low level saturation and warmth,
which may keep the area dry.

A more zonal flow pattern then establishes itself
on Sunday ahead of the next clipper system expected to head
towards the region. Current model runs show warm air advection
strong enough to ensure that precipitation with this system will
fall as rain. Winds could be quite gusty behind this system but
this far out the exact path of the system will strongly effect
both the wind strength and the precipitation type and chances.
&&

.AVIATION...for 06Z TAF Issuance
Issued at 1056 PM CST Tue Feb 28 2017

Very poor IFR flight conditions continue across the entire area.
Rain will mix with and changeover to snow overnight as a shortwave
tracks through the western Great Lakes. This system will bring
several inches of snow to the area overnight and into Wednesday.
Although previous models brought the heaviest snow across the
southern airports, recent models indicate this axis could shift
north. Conditions will improve to VFR Wednesday afternoon and
evening from northwest to southeast as the system moves away from
the region.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 4 AM to 6 PM CST Wednesday for
WIZ022-031-035>040-045-048>050-074.
&&

$$

SHORT TERM.....MPC
LONG TERM......Uhlmann
AVIATION.......Kurimski



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