Area Forecast Discussion
Issued by NWS Green Bay, WI

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000
FXUS63 KGRB 210319
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1019 PM CDT Sat May 20 2017

Updated aviation portion for 06Z TAF issuance

.SHORT TERM...Tonight and Sunday
Issued at 232 PM CDT Sat May 20 2017

The latest rap analysis and satellite/radar imagery show low
pressure centered over western Iowa, and associated warm front
extending east across central Illinois/Indiana early this afternoon.
Arcing band of rain is lifting north across central Wisconsin, and
approaching the Highway 29 corridor.  Thunderstorms have remained
well south of the area so far today, but the band of rain will
continue to lift north through the afternoon and should approach the
U.P. border by 00z.  Behind the rain, spotty showers and some
drizzle are occurring over Iowa and northern Illinois.  As the low
pressure tracks across the region, precip trends are the main
forecast concern.

Tonight...Low pressure will swing northeast into the northern
Mississippi Valley and western Great Lakes by late tonight.  Arcing
band of light to moderate rain will lift north ahead of the low and
across northern Wisconsin during the evening.  Behind the band of
rain, mid-level drying will drop inversion heights to 800-850mb,
which will temporarily put a halt to the rainfall, but will likely
leave areas of drizzle, low clouds, and possibly some fog.  Then a
occluded front will lift from southwest to northeast across the area
late tonight.  Some instability in the models along the boundary,
and forcing via potent shortwave could bring another band of showers
and a few thunderstorms to the area.  As a result, removed thunder
chances through midnight, but left the mention after midnight to
account for this possibility.  Lows only falling into the mid 40s
north and low 50s south.

Sunday...The occluded front will exit northeast Wisconsin by mid-
morning, bringing an end to the widespread shower and isolated
tstorm threat.  The incoming dry slot should bring dry weather for
the rest of the day to eastern WI.  But moisture wrapping around the
low will return occasional light showers to central and north-
central WI, mainly during the afternoon.  Highs will range from the
low 50s over the west to around 60 in the east.

.LONG TERM...Sunday Night Through Saturday
Issued at 232 PM CDT Sat May 20 2017

Main forecast concerns include precipitation trends for the first
half of the week, a period of dry weather late in the work week,
and a warm-up by the weekend.

A potent negatively-tilted short-wave trof will sweep across
northern WI late Sunday night into early Monday, so have boosted
pops to likely over north central WI during that period.
Following that, a cold front is expected to shift across the
forecast area later Monday into Monday night, then slow down or
stall out as a surface wave lifts northeast along the boundary on
Tuesday. Models all offer different timing with the wave, which
will impact whether or not any significant rains impact the
southeast part of the forecast area, or occur to our east.

Canadian high pressure will build into the region midweek, with
dry conditions expected from Wednesday night through at least
Friday. Abundant sunshine will cause temperatures to moderate,
with readings rising to above normal again by Friday and Saturday.
Return flow on the back side of the high may bring a small chance
of storms to our western CWA late Friday night or Saturday, but
the best precipitation chances should hold off until Saturday
night.
&&

.AVIATION...for 06Z TAF Issuance
Issued at 1019 PM CDT Sat May 20 2017

As a band of rain showers departs north of the state
at midnight, another band of showers along a frontal boundary,
with an isolated storm possible, will pass over the area late
tonight. In between these bands of showers, widespread IFR/LIFR
cigs with IFR/MVFR vsbys due to fog. Vsbys to improve after the
fropa late tonight or Sunday morning with cigs gradually
improving late Sunday morning into the afternoon to mainly mvfr
levels.
&&

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

$$

SHORT TERM.....MPC
LONG TERM......Kieckbusch
AVIATION.......TDH



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