Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 171642

Area Forecast Discussion
National Weather Service Green Bay WI
1142 AM CDT Mon Jul 17 2017

Updated aviation portion for 18Z TAF issuance

.SHORT TERM...Today...Tonight...and Tuesday
Issued at 322 AM CDT Mon Jul 17 2017

After a quiet period today into this tonight, showers and storms
return to the forecast area for Tuesday.

High pressure will shift eastward this morning as a frontal
system over the Northern Plains approaches the Western Great Lakes
Region. Return flow was already producing some lower end vfr
clouds over parts of central Wisconsin where surface dewpoints
were still in the mid 50s. Anticipate most of the afternoon cu
development to be confined to the western half of the state in the
area of higher surface dewpoints returning northward.

Progs in good agreement with convection from the approaching
frontal system over the Northern Plains may spill into parts of
north central Wisconsin mainly after midnight. Height 850 warm
prod working into northwest Wisconsin overnight creating some
marginal instability.

Convection will be on the increase Tuesday morning across the
northwest half of the state, including north central Wisconsin,
as a frontal boundary reaches the DLH area around 12z Tuesday.
Progs divert with the positioning of the frontal boundary for the
rest of the day with the slower NAM producing more rain across the
north, vs the faster GFS bringing the rain over much of the area,
but more spread out. GFS Pwats increase to 1.50 to 2.00 inches
along this front so locally heavy rainfall possible with storms.
Combination of convergence along the front, mu capes increasing to
1500-2000 j/kg Tuesday afternoon, and mid level winds increasing
in the wake of the short wave trough and more zonal flow, supports
the slight risk day 2 for part of the forecast area.

.LONG TERM...Tuesday Night Through Sunday
Issued at 322 AM CDT Mon Jul 17 2017

Thunderstorms are expected at the start of the long term as a cold
front enters the area from the northwest and mid level short wave
energy moves across Wisconsin. PWAT values in the 1.5 to nearly 2
inch range ahead of the front bring the potential for heavy
rainfall but the severe risk should wane with decreasing instability
as the night progresses.

Model differences in the timing of short waves, along with the
proximity of the frontal boundary, yields low confidence in
forecast PoPs after mid week. The southern part of the area has a
higher potential for showers and storms with the front to the
south and surface high pressure to the north. Left initial model
blend PoPs alone, which resulted in most periods having at least a
slight chance PoP in some part of the area.

High temperatures are expected to be above normal for Wednesday
and Thursday, then near normal for the rest of this week into the

.AVIATION...for 18Z TAF Issuance
Issued at 1124 AM CDT Mon Jul 17 2017

Good flying weather will be present into early this evening across
the region. A thunderstorm complex expected to develop over
northern Minnesota this afternoon remains projected by the hourly
high resolution guidance to turn to the right and pass over
western Wisconsin late this evening into overnight. Will stick
with these solutions, though the nam/arw move the complex close to
RHI. Otherwise, will see a warm front slide east across the
eastern half of the state tonight, and could spread sct to bkn
4kft ceilings across the area. Some potential for mvfr stratus to
develop late as well, but trying to pinpoint where and when is
very difficult. In any case, it would likely develop it small
patches. As a warm front approaches from the west tomorrow, clouds
will increase, with strong to severe storms to develop over
north-central and central WI during the mid to late afternoon




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