Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 151749
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1249 PM CDT Mon May 15 2017

Updated aviation portion for 18Z TAF issuance

.SHORT TERM...Today...Tonight...and Tuesday
Issued at 403 AM CDT Mon May 15 2017

Precipitation trends, severe thunderstorm potential and
temperatures are the main forecast concerns.

Scattered showers and a few thunderstorms have developed over
northern WI early this morning, in association with a H8 warm
front, 1-2km moisture convergence, mid-level frontogenetic
forcing, and MUCAPE of 400-600 j/kg. Some stronger convection
with near-severe hail was occurring near DLH. Models suggest
that this activity will remain over northern WI during the
morning and early afternoon. Convection should refocus over
central WI late in the day as the southwest SD/northeast Neb
short-wave trof approaches and a surface warm front lifts into
southern WI. High temperatures should warm into the upper 60s to
middle 70s, except around 60 near Lake Michigan.

The warm front will shift into central WI during the evening as
the short-wave trof moves through. Strong forcing combined with
PWATs of 1.00-1.50 inches will result in the potential for heavy
rainfall, especially over central and east central WI. It remains
to be seen whether the front will stall out due to convection or
continue to lift north overnight, so will just work a gradual
northward increasing trend in pops overnight. Elevated instability
(H8 LI`s of -4 to -6) and deep layer shear increasing to 50+ kts
supports the potential for a few marginally severe storms with
large hail north of the warm front. Lows will range from around
50 northeast to around 60 southwest.

On Tuesday, the warm front and best precipitation chances will
shift into northern WI, with central and east central WI getting
into the warm sector during the afternoon. A marginal severe
thunderstorm risk will continue near the warm front, but
current indications suggest that the warm sector will get capped
off. Will need to monitor this, as SBCAPE increases to 1500-2000
j/kg, mid-level lapse rates reach 7-8 c/km, and deep layer shear
remains sufficiently strong for organized storms. High
temperatures will range from the 70s north to the lower to middle
80s south.

.LONG TERM...Tuesday Night Through Sunday
Issued at 403 AM CDT Mon May 15 2017

Focus of the forecast remains centered around precip trends, and any
chance of severe weather.  An active period of weather is in store
for this upcoming week, thanks to the arrival of a more unstable
airmass, and a series of low pressure systems progged to cross the
region.  Like the past few nights, models agree well in the large-
scale, but have differences with smaller scale features and the
sensible weather at times.  Will try to mitigate these differences
with a blend of the ecmwf/gfs.

Tuesday night through Wednesday night...Chances of showers and
storms will remain relatively high over central and north-central WI
on Tuesday night compared to further east.  Will see a cold front
front slowly sag southeast through the night across northwest
Wisconsin.  Though the front itself could generate a few showers and
storms in this area during the evening, arrival of a shortwave could
lead to greater coverage overnight.  Skinny cape profiles do not
support much of a severe weather threat by this time, though a few
storms could drop some decent rains.  As a potent shortwave and low
pressure system swing northeast into the western Great Lakes on
Wednesday afternoon and Wednesday night, should see coverage of
showers and storms pick up again after a possible lull on Wednesday
morning.  Parameters suggest eastern WI stands to see the highest
chance of severe weather, though confidence is still rather low this
far out.  Heavy rainfall appears more of a threat along the cold
front over northern WI.  Instability wanes through Wednesday night,
though showers look to continue towards daybreak.

Rest of the forecast...Showers will likely continue on Thursday
morning until low pressure exits during the afternoon.  Behind the
low, should see Canadian high pressure build into the area, which
should provide dry and seasonable conditions through Friday.  Then
arrival of another low pressure system will bring wet weather for
the weekend.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1243 PM CDT Mon May 15 2017

Active weather pattern expected over the next 24 to 36 hours.
First band of showers and thunderstorms across north-central
and far northeast Wisconsin is expected to shift north and east
of the area by late afternoon. Meanwhile, another round of showers
and thunderstorms across Minnesota and Iowa will move into the
area late this afternoon and this evening. This should shift
east of the area around midnight or shortly after. Lastly, another
round of showers and thunderstorms is expected to develop across
central and east-central Wisconsin after midnight and shift into
northern Wisconsin towards daybreak. For the 18z tafs, added
showers and storms when I thought there was the best chance of
them occurring. Also, added low clouds and fog for a period of
time late tonight for the KRHI/KAUW/KCWA. Ceilings and visibilities
should slowly improve Tuesday morning across central and east-
central Wisconsin as a warm front shifts northward into northern
Wisconsin.

&&

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

$$

SHORT TERM.....Kieckbusch
LONG TERM......MPC
AVIATION.......Eckberg



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