Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 282026

Area Forecast Discussion
National Weather Service Green Bay WI
326 PM CDT SAT MAY 28 2016

Forecast discussion for routine afternoon forecast issuance

.SHORT TERM...Tonight and Sunday
Issued at 324 PM CDT Sat May 28 2016

Showers and thunderstorms are the main concerns in the short

A 500mb trough over the Plains today was forecast to move into
Wisconsin during the night, and a surface low to the west of the
area was to reach the northwest shores of Lake Superior by 12Z
Sunday. Mesoanalysis indicated at least 500J/kg of MUCAPE over
most of the forecast area, with in excess of 1,000 J/kg in parts
of central/north central Wisconsin. There was little to no CIN.
Radar mosaic time lapse showed showers and some thunderstorms,
from western upper Michigan across Wisconsin into Southeast
Minnesota/Iowa, moving north. Convection across the forecast area
was mainly focused in the vicinity of a warm front in north
central Wisconsin and a stationary front in western Wisconsin.

Would expect an increase in showers and storms during the late
afternoon and early evening, with rain continuing during the
night, mainly across the northwest 2/3rds of the forecast area.
There is a better chance for showers and storms over the remainder
of the area on Sunday as the surface low drags a cold front
across the state while the 500mb trough moves through Wisconsin.

Used a blend of the previous forecast and the some of the better
performing guidance numbers for lows tonight and highs on Sunday.

.LONG TERM...Sunday Night Through Saturday
Issued at 324 PM CDT Sat May 28 2016

Precipitation chances will be on the decline Sunday evening as a
mid level short wave with surface cold front shifts east of the
area. A ridge of high pressure quickly builds into the region for
Monday for overall quiet weather. This ridge was in advance of
Pacific trough of low pressure working into the Northern Plains.

Precipitation chances expected to be back on the increase late
Monday night into Tuesday as the Northern Plains upper trough and
frontal system tracks into the western Great Lakes region.
Convection expected to be on the increase over southwest
Wisconsin Monday night with a warm front lifting northward. Some
of this convection may reach central Wisconsin Monday
night...otherwise the models are in good agreement with the brunt
of this convection spreading over the area Tuesday into Tuesday
night. Scattered convection may be ongoing Wednesday over eastern
Wisconsin and in an occluded frontal region...and east of a dry
slot working into much of Minnesota and the western half of
Wisconsin. Another round of showers possible with the upper low
system and a secondary cool front passing over Wednesday night
into Thursday. The most recent GFS has quickened the departure of
this upper system for Thursday and therefore drier that the
lagging upper trough ECMWF solution.

The broad upper ridge builds over the western states late in the
week and into the weekend leaving the area in a northwest flow
regime. Medium range progs attempt to drop weak short waves over
the region Friday and Saturday in this northwest flow. Any
precipitation mention during this period will likely be minor and
more of the diurnal variety.

.AVIATION...for 18Z TAF Issuance
Issued at 1259 PM CDT Sat May 28 2016

Mainly MVFR conditions, with scattered IFR or VFR, across the
area at midday. Most of the showers were focused in the vicinity
of a warm front from north central Wisconsin northeast across
upper Michigan, and near a stationary front from southern
Minnesota to west central Wisconsin. There is a better chance for
showers and thunderstorms tonight as a surface low west of the
area moves north-northeast and a mid level trough moves into
western Wisconsin. Models focus rain mainly northwest of Green Bay
and the Fox Valley overnight with shift it a little farther east
during the day on Sunday.

Did not want to fill the TAFs with showers and/or storm through
18Z Sunday, so tried to focus on the times that condition looked
the best for rain. Expect the air mass across most of the area,
except for the far northeast corner of Wisconsin, to become more
unstable throughout the afternoon. Convective development could
occur along and subtle boundaries in the area so would not rule
out a chance for showers/storms at any time this afternoon through
Sunday morning.

Was on the fence whether to add LLWS to TAFs tonight as surface
flow becomes quite weak and models showed southwest winds of 20
to 30 knots at 0.5km AGL, but have left it out for now.



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