Area Forecast Discussion
Issued by NWS Green Bay, WI

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814
FXUS63 KGRB 280847
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
347 AM CDT SAT MAY 28 2016

Forecast discussion for routine morning forecast issuance

.SHORT TERM...Today...Tonight...and Sunday
Issued at 346 AM CDT Sat May 28 2016

Precipitation trends, potential for severe tstms and temperatures
will be the main fcst concerns.

An upper low over Nebraska and Kansas will move northeast into
western MN later today. Ahead of this feature, a short-wave trof
(currently over southwest WI) will lift north through the western
half of the forecast area this morning. In addition, a weak
surface low is expected to move toward north central WI, and pull
a warm front (currently situated over central WI) northward with
it. Expect the greatest pcpn coverage to occur across the
northwest half of the forecast area this morning, in association
with the s/w trof and sfc low. Partial clearing is possible over
the southeast part of the fcst area this afternoon, which should
result in enough destabilization (CAPE of 500-700 j/kg) for
scattered tstm development, especially near the lingering warm
frontal boundary. There is a marginal severe weather threat across
the region, and the best bet would with any discrete storms that
can develop near the warm front. It is difficult to say where the
front will reside this afternoon, but most models suggest
somewhere in north central and northeast WI.

Convection should weaken and decrease in coverage this evening,
as daytime instability wanes. However, showers and sct tstms will
increase again over nc/c WI overnight as a sharp upper trof pushes
into western WI. The trof and an associated cold front will sweep
across the forecast area on Sunday, bringing numerous showers and
sct tstms.

Used a blend of the better performing guidance sets for
temperatures the next couple days, but cloud and pcpn trends
will ultimately determine how warm we will get. Most places
should see highs in the 70s.

.LONG TERM...Sunday Night Through Friday
Issued at 346 AM CDT Sat May 28 2016

Mean flow to briefly go nearly zonal early next week, however the
development of a Western CONUS upper ridge is expected to have a
downstream shortwave trough develop and move east across the
northern tier of states toward mid-week. The timing of this
shortwave trough (and its associated cold front) into the Great
Lakes with precipitation chances to now be the main focus of the
extended forecast. Cooler/drier air is then expected for later
next week as surface high pressure builds into the region.

Any spotty leftover shower/thunderstorm activity from the exiting
initial shortwave trough should end early Sunday evening across
the north. Otherwise, expect to see decreasing clouds and light
winds over the region during the overnight hours which may allow
for some late night fog to develop. Min temperatures to be in the
lower 50s north, mid to upper 50s south. Weak area of high
pressure to be in our general vicinity for Memorial Day, however
there appears to be enough low-level moisture around such that
daytime heating may increase instability parameters in the
afternoon. While a stray shower or thunderstorm cannot be
completely ruled out, feel the instability may not be strong
enough to all precipitation to develop, thus have kept Memorial
Day dry for now. Max temperatures to range from the mid to upper
70s north/lakeshore, to the upper 70s to lower 80s south.

Attention then turns to the west, where a new shortwave trough is
forecast to be moving across the northern High Plains Monday
night. A SW flow aloft is expected to develop across the Plains/
Midwest with moisture beginning to get lifted toward WI. Models
indicate this moisture will interact with a warm front draped from
SW MN into IA to generate a new round of showers/thunderstorms.
Most of this activity should stay to our south and west Monday
night, however will probably need to carry a minimal pop for our
SW counties, especially after midnight. Otherwise, look for some
increase in clouds overnight with min temperatures around 50
degrees north, mid 50s south. This band of showers and
thunderstorms are forecast to lift newd and gradually overspread
NE WI on Tuesday as the warm front moves into WI and several
shortwaves lift into the region within the SW flow aloft. Highest
pops placed over central WI where the precipitation will reach
first and these values may need to be raised further once
confidence in timing gets better. Thicker clouds and advancing
precipitation will limit diurnal heating with max temperatures on
Tuesday ranging from around 70 degrees near Lake MI, lower to
middle 70s north and middle to upper 70s south.

Shower and thunderstorm chances still look good into Tuesday night
as the shortwave trough pushes across the northern Plains and a
cold front preceding the trough moves into roughly western WI by
12z Wednesday. While the models agree in taking the shortwave
trough eastward into the Upper MS Valley on Wednesday, they begin
to diverge with the forward speed of the cold front and potential
for a dry slot to rotate into WI. The GEM sides with the ECMWF as
far as the dry slot goes, but with the cold front expected to be
pushing across the state, hard to buy into the dry forecast these
two models are showing. May attempt to lower pop values down a bit
compared to the previous forecast, but not drop pops altogether.
Max temperatures on Wednesday should be a couple of degrees cooler
than Tue with upper 60s near Lake MI, lower 70s north and mainly
mid 70s south.

Precipitation trends should begin to diminish to a certain degree
as the cold front shoves farther to the east Wednesday night into
Thursday. However, the trailing shortwave trough is progged to
reach the Western Great Lakes on Thursday, so the big question is
whether there will be any moisture left over the region or will
the cold front have taken all the moisture east with it?
Typically, cold fronts do a good job in stripping the best low-
level moisture, leaving nothing behind for any trailing surface
boundary or mid-level system. May end up with a token pop just in
case the air mass aloft cools enough to steepen lapse rates.

By the end of the work week, NE WI to reside under a NW flow aloft
with an area of high pressure building into the region. Do not see
enough evidence of any triggering mechanism for precipitation,
thus would like to go dry on Friday. Temperatures by the end of
the week could actually drop close to, if not a degree or two
below normal.
&&

.AVIATION...for 06Z TAF Issuance
Issued at 856 PM CDT Fri May 27 2016

After the recent rains and with a humid air mass across the area,
expect flight conditions to deteriorate significantly overnight.
But confidence in how widespread the fog becomes is very low. Plan
to stick close to the scenario in the current TAFs.
&&

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

$$

SHORT TERM.....Kieckbusch
LONG TERM......Kallas
AVIATION.......Skowronski



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