Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 191953
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
253 PM CDT Wed Apr 19 2017

Forecast discussion for routine afternoon forecast issuance

.SHORT TERM...Tonight and Thursday
Issued at 252 PM CDT Wed Apr 19 2017

Several issues will need to be dealt with over the next 24 hours
centered around the passage of a low pressure system, associated
warm and cold fronts. Main concern will be heavy rain with most of
northeast WI expected to see around an inch of precipitation.
There is also a marginal risk of severe thunderstorms over parts
of central/east-central WI tonight. This will all be followed by
lingering light rain showers and cooler temperatures on Thursday.

The 19z MSAS surface analysis showed an area of high pressure
stretched from Ontario southward into the Great Lakes. Meanwhile,
the aforementioned area of low pressure was located over the
central Plains with a warm front extended eastward across northern
MO. Visible satellite imagery indicated that some of the pesky low
clouds had mixed out over parts of northeast WI this afternoon,
however middle and higher clouds ahead of the surface low are
already overspreading the state, thus any clearing would be brief.

The surface low is forecast to track northeast across the Midwest
this evening and reach central WI by 12z Thursday. This a little
farther north which will allow the warm front to lift into our
southern tier of counties (Wautoma-Manitowoc) during the late
night hours. As the surface low/warm front approach, expect to see
a band of showers/thunderstorms move across WI under very strong
lift/low-level moisture transport. PW values climb into the
1.00-1.25" range tonight, thus locally heavy rainfall is expected
with most locations receiving between 0.75-1.25" of rain. Will
continue with an ESF product for the heavy rain and also mention
in the HWO. As for the severe threat, the slight northward shift
of the surface low/warm front would allow more of an unstable air
mass to reach parts of central and east-central WI tonight. CAPES
could approach 400 J/KG with 0-6km bulk shear values > 50kts. An
isolated strong thunderstorm is possible with large hail or
damaging winds being the primary threats.

The surface low moves east-northeast through the rest of eastern
WI Thursday morning before departing toward eastern Lake Superior
or northern Lower MI Thursday afternoon. A cold front will
accompany the surface low with winds eventually switching to the
west-northwest. In addition to these surface features, a mid-level
shortwave trough is progged to push into the region Thursday
afternoon to keep a level of forcing over northeast WI. Models
continue the precipitation chances over the entire forecast area
during the morning hours, then focus additional chances mainly
over the north in the afternoon where better wrap-around/
deformation zone to exist. The west-northwest winds will also draw
CAA into WI, therefore temperatures should be at or below normal
with readings only around 40 degrees far north, lower to middle
50s over parts of central/east-central WI.

.LONG TERM...Thursday Night Through Wednesday
Issued at 252 PM CDT Wed Apr 19 2017

A small chance for some lingering precipitation will remain in the
north early Friday as the low pressure system exits the region.
There will be a small chance to see some snow or a wintry mix as
temperatures aloft and near the surface drop below freezing.

Surface high pressure then develops as a mid level ridge moves in
behind the cold front. This should keep conditions dry and mostly
clear for a pleasant weekend with some sunshine. Forcing along the
northern border of Wisconsin Sunday night into Monday may be
strong enough to produce a few isolated showers with possible rain
or snow showers into very early Monday, with little to no
accumulation.

The next system then approaches as a cold front moves through the
region Monday evening. Rain is likely over much of the area, with
a chance to transition to some snow showers in the north as
temperatures drop into Tuesday morning. A weak surface ridge will
follow as this system exits Tuesday evening which should clear out
the area until the next round of precipitation follows on
Wednesday.

Temperatures overall will be within a few degrees of normal during
this period. Highs should be mostly in the 50s with a brief touch
into the 60s on Saturday and lows will generally be in the middle
to upper 30s.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1239 PM CDT Wed Apr 19 2017

Primarily MVFR cigs to rule into early this evening, although some
brief VFR cigs are possible this afternoon as some mixing does
occur before more clouds arrive from the southwest. An area of low
pressure is forecast to move across the Midwest into Wisconsin
tonight and pull a warm front northward into Wisconsin as well.
Expect a band of showers and thunderstorms to accompany these
surface features with some of this precipitation heavy at times.
Look for cigs/vsbys to lower in the MVFR range this evening,
eventually reaching LIFR/IFR conditions overnight into Thursday
morning as the surface low moves by. Have introduced a brief
period of LLWS this evening across all northeast Wisconsin TAF
sites as winds just above the surface crank up over 35 knots. The
low clouds are expected to hang around through at least Thursday
morning and eventually climb to IFR/MVFR conditions Thursday
afternoon.
&&

.MARINE...
Issued at 252 PM CDT Wed Apr 19 2017

An area of low pressure is forecast to slowly strengthen as it
moves toward WI tonight. As the pressure gradient begins to
tighten, easterly winds will increase over eastern Wisconsin
later tonight and Thursday morning. Gale force wind gusts are
expected near Death`s Door and around the northern portion of
Door County during this period. Therefore, a Gale Warning remains
in effect for the central Bay of Green Bay and the Lake Michigan
nearshore waters north of Sturgeon Bay. Farther south closer to
the low, winds will gust to 20 to 25 knots along with higher
waves. A small craft advisory remains in effect for the rest of
the zones starting tonight and lasting through Thursday night for
the Lake Michigan nearshore zones.
&&

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

$$

SHORT TERM.....AK
LONG TERM......Uhlmann
AVIATION.......AK
MARINE.........AK



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