Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 232340

Area Forecast Discussion
National Weather Service Green Bay WI
540 PM CST Thu Nov 23 2017

Updated aviation portion for 00Z TAF issuance

.SHORT TERM...Tonight and Friday
Issued at 245 PM CST Thu Nov 23 2017

Temperature trends will be the primary issue through Friday.

Surface data suggests a subtle wind shift working over eastern
Wisconsin this afternoon was associated with an 850 trough sliding
over the area. After a period of weak ridging in its wake,
southwest winds will redevelop and the warming trend will
intensify.  First forecast issue tonight will be overnight lows.
Anticipate some evening lows with light winds and clearing skies
before 850 mb temps rise with the increasing winds aloft.

Height 850 temps expected to climb to at least +12 C by noon
Friday, with many locations climbing well into the 50s. Winds will
be gusty and if sufficient boundary layer mixing can occur, a few
wind gusts to at least 30 mph will be possible midday Friday, but
usually this time of the year, the inversion is rather robust.
These warmer temps may need to be expanded further north, but at
this time, clouds and scattered showers will be dropping into the
state during the day. The progs continue to indicate a faster
trend of moving this frontal system and associated precipitation
over the area on Friday. Lapse rates become very steep in the mid
levels Friday but dry lower levels producing saturation issues
with respect to shower coverage. The 850 mb trough is already
departing eastern wisconsin toward late afternoon.

.LONG TERM...Friday Night Through Thursday
Issued at 245 PM CST Thu Nov 23 2017

Expect low amplitude upper level flow to prevail across the region
into early next week.

Some precipitation may linger into Friday night as a surface low
moves away from the state and a mid level short wave passes.
Light rain is possible in eastern Wisconsin Friday evening and
there may be some rain or snow in north central Wisconsin
throughout the night. Colder temperatures return on Saturday
behind the departing low and there is still a slight chance for
snow showers in far north central Wisconsin.

Surface high pressure and a mid level ridge will bring sunny skies
for Sunday, so highs should be at least a few degrees warmer than
Saturday. Warm advection ahead of the next surface system should
allow the entire forecast area to reach the 40s on Monday, and
some lower 50s are possible in central Wisconsin.

The timing of a cold front that is expected to move across
Wisconsin differs among the models. The GFS took it through the
entire forecast area by 12Z Tuesday, while the ECMWF had it about
half way through, and the Canadian only had it reaching northwest
Wisconsin by then. Made no changes to the model blend after 00Z
Tuesday due to the differences among the models.

Nothing more than slight chance PoPs until Thursday when another
surface system brings rain and/or snow chances to part of the
area, mainly during the afternoon. Cooler, but still above
normal temperatures can be expected on Tuesday, but highs on
Wednesday and Thursday should be within a few degrees of normal.

.AVIATION...for 00Z TAF Issuance
Issued at 533 PM CST Thu Nov 23 2017

VFR conditions will prevail tonight into Friday morning, as mid-
level clouds arrive ahead of an approaching frontal system. The
main aviation concern will be LLWS late this evening through mid-
morning Friday, as west-southwest winds increase to 40-45 kts just
off the surface. Surface wind gusts should increase due to daytime
heating later Friday morning.

Showers are expected to develop over northern WI late Friday
morning, and over the rest of the forecast area as the front
arrives during the afternoon. MVFR ceilings will develop over
north central and parts of central and far northeast WI during
the afternoon.



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