Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 262305

Area Forecast Discussion
National Weather Service Green Bay WI
605 PM CDT Thu Apr 26 2018

Updated aviation portion for 00Z TAF issuance

.SHORT TERM...Tonight and Friday
Issued at 306 PM CDT Thu Apr 26 2018

Weak cold front moving across northwest Wisconsin
this afternoon will move across the remainder of the forecast
area during the early evening hours. It could produce scattered
showers, especially as it gets closer to the lake and bay where
low level moisture is a little better. Skies should clear for a
little while behind the front later tonight, which will make
temperature forecasting difficult. Places that still have snow
cover in the north could get down into the lower to middle 20s.

A clipper system will rapidly move across the area Friday, and
bring some precipitation. 850/925/sfc temperatures would suggest
that some snow is likely in the far north early Friday before it
warms up. Think an inch or less is the most likely amount, but
locally higher amounts are not out of the question. Cloudy skies
and rain will hold down temperatures Friday into the 40s in most
places. Rainfall amounts should be low enough not to aggravate
minor flooding in some rivers and streams.

.LONG TERM...Friday Night Through Thursday
Issued at 306 PM CDT Thu Apr 26 2018

A rather amplified flow is expected across the CONUS well into
next week. Initially, we are looking at closed upper lows over the
Pacific Northwest and New England with an upper ridge over the
central CONUS this weekend. Models agree that by early next week
the flow translates to an upper trough western CONUS/upper ridge
eastern CONUS with a southwest flow over the central CONUs
bringing a taste summer to northeast WI. The impending southwest
flow will also pull gulf moisture north, bringing several rounds
of showers/storms to WI which might aggravate the high river

Chance of rain or rain/snow showers will continue into Friday
evening across east-central WI as the shortwave trough exits the
region. Winds are expected to pick up a bit behind the system
(especially across eastern WI) as the pressure gradient tightens
up between the low pressure over the eastern Great Lakes and high
pressure located over western Ontario. Otherwise, the rest of the
night will see clouds on the decrease with min temperatures in the
lower to middle 20s north-central WI, to the lower 30s across
east-central WI. This area of high pressure is forecast to build
into the western Great Lakes region on Saturday, providing for
sunny, but cool conditions by late April standards. Winds may
still be little on the breezy side into Saturday morning before
slowly diminishing later Saturday afternoon. Look for max
temperatures to range from the middle to upper 40s north-central/
near Lake MI, to the lower to middle 50s elsewhere.

This broad area of high pressure is expected to stretch from just
south of Hudson Bay, through the western Great Lakes, all the way
to the Gulf on Saturday night. Clear skies and light winds will
bring another cold night to northeast WI with min temperatures in
the lower to middle 20s north, upper 20s to around 30 degrees
south. The surface high finally shifts to the east, allowing winds
to gradually become south-southwest. These winds will start to
pull warmer air into the region with max temperatures 5 to 15
degrees warmer than Saturday. This would bring readings into the
lower 50s near Lake MI, mainly upper 50s to lower 60s farther

A surge of WAA into WI is expected for Sunday night and after a
clear evening, mid/high clouds should begin to overspread the
region during the overnight hours. Models pretty much bring a
chance of rain showers across northeast WI once the atmosphere
saturates on Monday. The better instability remains to our south
and west, however mid-level lapse rates do steepen in the
afternoon, so a rumble or two of thunder cannot be ruled out over
central WI. Max temperatures for Monday to range from the lower
60s near Lake MI, upper 60s to lower 70s inland. Precipitation
chances appear to briefly trend down Monday night as the
isentropic lift weakens and an approaching cold front reaches the
Upper MS Valley by 12Z Tuesday. Precipitation chances should be
on the increase once again by Tuesday afternoon as the cold front
pushes toward the MN/WI border. Low-level moisture will continue
to slowly increase through the day with dew points approaching 50
degrees over central/east-central WI. Instability will also be
increasing with models showing steep mid-level lapse rates and
Capes up to 500 J/KG. In addition, models indicate several
individual shortwaves lifting northeast within the southwest mean
flow aloft. Therefore, have kept a chance of showers/thunderstorms
in the forecast for Tuesday with max temperatures in the middle
60s near Lake MI, lower to middle 70s elsewhere.

As the cold front sweeps into WI Tuesday night, anticipate a
continued need for a chance of showers/thunderstorms in the
forecast. We will need to watch QPF amounts closely with river
levels still elevated by the snowmelt/earlier rains. It appears
that this system exits the area by the start of Wednesday, thus a
cooler/drier day is forecast for northeast WI. Max temperatures
will be slightly above normal with lower to middle 60s north-
central/lakeshore, upper 60s to around 70 degrees elsewhere.

The big question for Wednesday night/Thursday will be where the
cold front to be situated as a surface wave is progged to ride the
frontal boundary. If the cold front can be pushed far enough
south, northeast WI would not be impacted. If the front is still
close enough, northeast WI could see another round of showers with
locally heavy rain. Not good for the rivers! For now, have split
the difference and keep pops at a chance. Max temperatures to be
primarily in the upper 50s to lower 60s.

.AVIATION...for 00Z TAF Issuance
Issued at 605 PM CDT Thu Apr 26 2018

An approaching cold front will bring increasing clouds as well as
the chance for showers this evening. A period of MVFR cigs is
possible in the far north behind the front. A clipper system will
bring clouds and some light precipitation Friday. The
precipitation could begin as snow north of Rhinelander with rain
elsewhere. Flight conditions will generally be MVFR, with local
IFR possible. The precipitation will end Friday evening, possibly
as rain mixed with snow.

Issued at 306 PM CDT Thu Apr 26 2018

Very low relative humidity values below 30 percent are expected
during the afternoon and early evening hours Saturday and Sunday
north and west of the Fox Valley. High temperatures Saturday will
be in the middle 40s to lower 50s, and in the upper 50s to middle
60s on Sunday. North winds at 10 to 20 mph on Saturday are
expected to switch to the southwest at around 10 mph on Sunday.



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