Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 141933
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
233 PM CDT Mon Aug 14 2017

Forecast discussion for routine afternoon forecast issuance

.SHORT TERM...Tonight and Tuesday
Issued at 233 PM CDT Mon Aug 14 2017

The latest RAP analysis and satellite/radar imagery show shortwave
troughing moving across the western Great Lakes early this
afternoon.  Showers have been most widespread over northern WI so
far today, though the mesoanalysis indicates 200-400 j/kg of surface
based instability developing over central to eastern WI.  Therefore,
cannot rule out scattered showers and isolated storms developing in
these areas later this afternoon.  Latest HRRR also indicates this
remains a possibility.  Looking upstream, broken clouds remain over
western WI and Minnesota, and it looks rather difficult to see these
clouds mixing out through the afternoon.  Forecast concerns revolve
around precip trends through the evening, then cloud trends.

Tonight...The shortwave trough will continue to move east across the
region this evening before departing overnight.  Area of deepest
moisture suggests that northern WI will continue to see the greatest
coverage of showers, but higher res models also show isolated to
scattered activity lingering elsewhere through late in the evening
or early overnight.  In general though, the chance of precip will be
diminishing from west to east tonight.  Plenty of lower cigs
upstream over Minnesota, so kept sky conditions in the mostly cloudy
range through 12z.  If any holes in the clouds develop, fog could
develop, but confidence in location is rather low.  With the cloud
cover, temps ranging from near 50 in the north to low 60s in the
south.

Tuesday...Mostly cloudy conditions look to start out the day, then
models indicate skies will partially clear into a cu field with the
heat of the day.  Otherwise, high pressure will ensure a dry and
seasonable day.  Highs ranging from the mid to upper 70s.

.LONG TERM...Tuesday Night Through Monday
Issued at 233 PM CDT Mon Aug 14 2017

High pressure over Lake Superior is expected to shift into eastern
Ontario Tuesday night, but should still have enough influence to
maintain a dry forecast over northeast WI.

The previous shift mentioned that the current system had trended
slower over the past several days, and a similar trend seems to be
setting up for the midweek system. Models are have backed off on
the arrival of precipitation on Wednesday, with WAA and a short-
wave trof only bringing a chance of showers to our southwest
counties in the afternoon.

The stronger dynamics are set to arrive Wednesday night, with a
couple short-wave trofs, a H8 warm front and the RRQ of an upper
jet (late). In addition, precipitable water values are forecast
to increase to 1.6 to 2.0 inches, so moisture will be plentiful.
Plan to carry likely pops over the entire forecast area. Likely
pops will continue in eastern WI ahead of a cold front on
Thursday, but precipitation should become more scattered elsewhere
as a dry slot arrives. Marginal instability and shear support a
low-end severe weather threat ahead of the cold front, but only if
the surface low tracks far enough north to bring the warm sector
into the forecast area. The ECMWF supports a low track farther to
the south, which would suggest more of a heavy rainfall threat
than a severe threat.

Significant CAA will occur in the wake of the low late Thursday
into Thursday night, with H8 temperatures falling to +9 to +10 C.
The cool NNW flow could lead to some lake-enhanced showers in far
north central WI and over Door county.

High pressure will bring a period of mainly dry weather and
gradually moderating temperatures through the weekend. An
approaching frontal boundary may trigger scattered showers and
thunderstorms early next week, but there are timing differences
in the medium-range models, so details will need to be ironed
out later.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1151 AM CDT Mon Aug 14 2017

Scattered showers and isolated storms will continue to move east
across the area for the rest of the afternoon into this evening.
Ceilings should continue to hold up well this afternoon, though
could drop locally to mvfr within the heavier showers/storms.
Short range models continue to show that showers will diminish
this evening. But ample mvfr clouds upstream and statistical
guidance suggest ceilings will lower overnight. Any ifr/mvfr cigs
to improve quickly on Tuesday morning after 14-15z.
&&

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

$$

SHORT TERM.....MPC
LONG TERM......Kieckbusch
AVIATION.......MPC



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