Area Forecast Discussion
Issued by NWS Green Bay, WI

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725
FXUS63 KGRB 182338
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
638 PM CDT Fri May 18 2018

Updated aviation portion for 00Z TAF issuance

.SHORT TERM...Tonight and Saturday
Issued at 219 PM CDT Fri May 18 2018

The main forecast concerns to be on precipitation chances for
later tonight/early Saturday morning for eastern WI and small
chances across northern and central WI Saturday afternoon.

The 19Z MSAS surface analysis indicated an area of high pressure
located over Quebec with ridging extended southwest into the
western Great Lakes region. An area of low pressure was located
near Fargo, ND with a cold front extended southwest into the
central High Plains. Meanwhile, a large band of clouds associated
with a nearly closed upper low well to our south, was making a
push northward along with scattered light rain showers.

Models remain in sync with the northeast movement of a weak system
into eastern IL/western IN vicinity by 12Z Saturday. Clouds are
expected to lift/overspread east-central WI this evening and
central/far northeast WI overnight. Precipitation chances to
steadily increase across eastern WI mainly after midnight with the
highest pops placed east of a line from Oshkosh to Sturgeon Bay.
The western edge of the pops to reach roughly from Wautoma to Iron
Mountain, leaving north-central and parts of central WI dry
tonight. Min temperatures to range from the middle to upper 40s
north/near Lake MI, upper 40s to lower 50s south.

This system is forecast to continue moving northeast into the
eastern Great Lakes on Saturday, with a chance of showers
lingering over eastern WI during the morning hours. Just as this
system loses its influence on our weather, a cold front is progged
to move through most of northeast WI Saturday afternoon. The
better forcing is expected to be to our north and the models
suggest most of any shower activity to be post-frontal. Therefore,
precipitation chances with this cold front look minimal at this
time and be focused across central/northern WI for the afternoon
hours. Max temperatures to range from the lower to middle 60s near
Lake MI, to the middle 70s over central WI.

.LONG TERM...Saturday Night Through Friday
Issued at 219 PM CDT Fri May 18 2018

Focus is on rain chances late in the weekend and early in the
week.

A cold front continues to drop across Wisconsin Saturday evening
into Sunday morning, but the overall trend is for the front to
pass through dry. The GFS is the most liberal with generating some
QPF, but even that is only a couple hundreths. Model soundings
are incredible dry through Sunday and think it will be rather
tough to get any pcpn, especially across the north. The best
chance for any showers would be across the far southern forecast
area Sunday afternoon associated with a surface low around western
Iowa, but models still vary on how far north any rain would reach
on Sunday so confidence is still rather low.

This low moves closer to Wisconsin Sunday evening/Monday as a
mid- level shortwave also passes across the state. This is the
most likely feature to generate any rain showers and we have a
little more moisture to work. But, models still diverge on timing
with the NAM/Euro moving everything east by early Monday and the
GFS/Canadian moving much slower and keep precip through Monday
night. Kept a blended solution for now.

More confident that sfc high pressure will build in for the
midweek and keep the area dry. Although, the latest 12Z GFS now
brings in some rain for Thursday. Not too eager to add any pcpn
to the forecast as other models are still dry, but included a
slight chance of showers Thursday afternoon.

Beyond Thursday, lower confidence in forecast. Trends indicate we
might have a chance of getting some rain across the area Friday or
this weekend, but timing details are still rather messy.

Temperatures will be around or slightly below normal on Sunday and
Monday due to more clouds/precip potential, but could need
adjusting as the pcpn forecast evolves. Temps the rest of the week
will be above normal with lows in the 40s/50s and highs in the
70s away from Lake Michigan.
&&

.AVIATION...for 00Z TAF Issuance
Issued at 637 PM CDT Fri May 18 2018

VFR conditions will continue through the evening
hours. Surface low pressure approaching from the south, and a cold
front approaching from the west, will combine to bring clouds to
the area later tonight through Saturday. Light rain and MVFR
conditions are possible east of an IMT to STE line late tonight
through midday Saturday.
&&

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

$$

SHORT TERM.....Kallas
LONG TERM......KLB
AVIATION.......RDM



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