FXUS63 KGRB 161754

Area Forecast Discussion
National Weather Service Green Bay WI
1254 PM CDT Thu Aug 16 2018

Updated aviation portion for 18Z TAF issuance

.SHORT TERM...Today...Tonight...and Friday
Issued at 322 AM CDT Thu Aug 16 2018

Areas of dense fog will dissipate a few hours after sunrise. An
upper trough moving across Wisconsin later today and tonight will
provide some upper support for precipitation today, though not
very much. The upper wind field remains very light, with less than
20 kts of wind at 500 mb. Northeast winds around a weak surface
high over Lake Superior will bring slightly drier air into
northeast Wisconsin, which will likely inhibit convection there to
some degree. Highs today will be about 5 degrees above normal
again. Whatever showers and thunderstorms do materialize later
today could produce heavy rain due to their slow movement.

Showers and thunderstorms should slowly dissipate after the sun
sets this evening. Cloud cover will keep lows a little above

Friday will be partly sunny and warm, with a slight chance of
showers or thunderstorms in east central Wisconsin. Highs will be
a few degrees above normal.

.LONG TERM...Friday Night Through Wednesday
Issued at 322 AM CDT Thu Aug 16 2018

Long term highlighted by pretty quiet weather Friday night into
Sunday afternoon, unsettled Sunday afternoon/night into Monday
night, then pretty quiet again for the middle of next week. Temps
will start off above normal for the weekend, then fall back near
or slightly below normal early next week.

Fairly quiet weather conditions are expected Friday night into
Sunday afternoon as upper trough pushes well east of the area and
ridging builds into the western Great Lakes. However, it should
be noted that the Canadian develops some diurnal showers on
Saturday (along with the GFS/ECMWF but to our south/west). Hoping
they are over-doing the moisture (and therefore CAPE) and weak
subsidence will keep things dry but did bump up cloud cover
slightly. If showers were to form, it should be very isolated.
Mostly clear skies and light winds at night will provide for good
radiational cooling conditions, which will allow some fog to
develop in the late evening and overnight hours Friday and
Saturday nights. Highs this weekend look to be mainly in the 80s
with humidity levels slowly creeping up. Lows will mainly be in
the 50s across the north and in the lower 60s across central and
east central WI.

Attention then turns to the approaching upper trough and
developing surface low pressure system Sunday night into Monday
night. GFS continues to paint a very different picture than the
ECMWF and Canadian. GFS has not backed off with a much more
progressive and weaker system both aloft and at the surface,
bringing a cold front across the area Monday afternoon and
tracking the weak surface low well to our south in the Ohio
Valley. Prefer to lean toward the ECMWF/Canadian which show a
slower, deeper system tracking across the Great Lakes on Monday
into Monday night. The GFS ensembles did come into a little
better alignment with the operational run, so something to watch.
Exact track and timing still tough to nail down obviously with so
much disagreement, but best chances for a widespread precip event
looks to be Monday afternoon and evening either with the cold
front (GFS) or with a more wrapped up low pressure system
(ECMWF/Canadian). Severe weather threat still looking low, with
heavy rain probably the biggest threat as precipitable waters
climb to over 1.5 inches.

The cold front/low pressure will exit to the east late Monday
night or Tuesday morning. While the heavier precip will end and
some drier air works into the region, models still show a
secondary shortwave (ECMWF the strongest) diving across the Great
Lakes on Tuesday. This feature combined with cyclonic flow behind
the departing low pressure, could lead to lingering shower
activity and more clouds. However, using a model blend, will go
with a dry forecast for now. Cooler and less humid conditions are
expected early next week, but just how much cooler will be
dependent on how much cold air advection occurs behind the
departing system and how much sunshine there is.

.AVIATION...for 18Z TAF Issuance
Issued at 1254 PM CDT Thu Aug 16 2018

Still having to deal with MVFR cigs across north-central WI this
afternoon, however cigs should rise back to VFR conditions toward
mid-afternoon. Scattered showers/thunderstorms are expected across
northern and central WI this afternoon into this evening as a
shortwave trough approaches and daytime heating brings some
instability. The precipitation is forecast to gradually diminish
later this evening, setting the stage for more fog development
with cigs/vsbys over northern and central WI perhaps reaching LIFR
conditions from 09Z to 13Z Friday. The fog will then be slow to
burn off Friday morning, but improve by late morning. Cannot rule
out additional precipitation chances on Friday as the shortwave
trough starts to exit the region.



LONG TERM......Bersch
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