Area Forecast Discussion
Issued by NWS Green Bay, WI

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660
FXUS63 KGRB 301746
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1246 PM CDT Sun Apr 30 2017

Updated aviation portion for 18Z TAF issuance

.SYNOPSIS...
Issued at 350 AM CDT Sun Apr 30 2017

Chilly and blustery with rain at times through tomorrow, then
drier weather with temperatures returning closer to seasonal
normals for the rest of the upcoming work week.

The large scale upper features across North America will become
progressive during the upcoming work week. They should migrate
about ohe-half wavelength downstream before locking into place
and amplifying into a blocking regime. The new pattern will
feature deep troughs/closed upper lows near the coasts with a
sharp mid-continent ridge in between--just the opposite of what
we`ve had for about the past 10 days.

A strong cyclone ejecting out of the Plains will result in
another round of significant rainfall today through Monday night.
The developing northwest upper flow in the wake of the departing
cyclone favors lighter/more scattered-type rain events, providing
an opportunity for things to dry out some. Temperatures will
remain below normal through the start of the upcoming work week,
then closer to normal for the rest of the period.
&&

.SHORT TERM...Today...Tonight...and Monday
Issued at 350 AM CDT Sun Apr 30 2017

The main forecast issue continues to revolve around the details of
the precipitation forecast. Widespread convection to our south has
thus far intercepted much of the moisture surging north off the
Gulf, allowing for only some small areas of light rain across the
forecast area thus far. Think the overall coverage of the rain
will gradually increase and advance farther north into the area
today, though there will certainly be dry periods across the area
as well. And there is still some question concerning when or even
if the rain can reach the far north today.

There should be an uptick in the precipitation this evening as the
main upper system begins to approach the area. The heaviest rains
should occur in advance of dry slot driving toward the area from
the south. Spread the chance for thunder northward with the main
rain band as some elevated instability will likely be present.
Rains will taper back to scattered showers after midnight across
the southern part of the area, and across the rest of the area
late tonight or early Monday.

The cyclone center will track across the area Monday, maintaining
periods of showers. The system will be stacked and weakening by
that time, and models are not very aggressive with cooling aloft
with the upper system, so kept the precipitation all liquid.

.LONG TERM...Monday Night Through Saturday
Issued at 350 AM CDT Sun Apr 30 2017

Models remain in good agreement with the handling/departure of the
deep cyclone from the Great Lakes into southeast Canada into mid-
week. The majority of models then show a gradual shift in the
large-scale pattern with a new upper trough moving into the
eastern Pacific, the eastern Pacific upper ridge shifting east
into the Rockies and a downstream deep upper trough setting up
over the eastern CONUS late in the week. This pattern shift would
bring a NW flow aloft into WI and keep temperatures at least
slightly below normal through next Friday. Precipitation chances
would become more spotty, focused around Thursday as the upper
trough heads east.

The stacked system continues to track northeast toward eastern
Lake Superior/extreme southeast Ontario Monday night. Rain showers
to persist over northeast WI for much of the night as a cold front
sweeps across the region in the evening, followed by a cool,
cyclonic flow around this system overnight. The main concern for
Monday night will be precipitation type as the cooler air wraps
into the forecast area. Anticipate snow to mix with the rain
north/parts of central WI toward midnight and persist in this
matter through daybreak. There could be a dusting of snow on
grassy surfaces across the north, otherwise rain amounts appear
light as deeper moisture to have moved either north or east. Min
temperatures to be in the lower to middle 30s north, middle 30s to
around 40 degrees south. The cool, cyclonic flow lingers across WI
into Tuesday, but in a weakening state through the day. Expect at
least a minimal chance of showers to persist (mixed with snow
early north), along with blustery west-northwest winds. Look for
another unseasonably cool day with max temperatures in the lower
40s far north-central (Vilas County), to around 50 degrees south.

We finally get rid of the precipitation chances Tuesday night as
a weak area of high pressure moves into the western Great Lakes
region. The arrival of at least some drier air should be enough to
allow skies to become partly cloudy during the night. The break
in the cloud cover, coupled with light north winds, will send min
temperatures down in the upper 20s to around 30 degrees north,
lower to middle 30s south. This area of high pressure is expected
to slowly push across the Great Lakes on Wednesday and initially
bring a decent amount of sunshine to northeast WI. There might be
a gradual increase in afternoon clouds into central WI ahead of a
weak system dropping southeast toward the Upper MS Valley. More
sunshine should allow max temperatures to warm into the lower 50s
near Lake MI, but mainly in the middle to upper 50s elsewhere
(still about 5 degrees below normal).

Clouds should continue to slowly increase over WI Wednesday night
with a small chance for light rain showers on Thursday. While this
little system has modest mid-level forcing, there are questions as
to moisture availability as a much larger system over the Deep
South will tend to rob any potential inflow of gulf moisture from
reaching WI. Have kept a small chance pop in the forecast for
Thursday with max temperatures primarily in the upper 50s north to
around 60 degrees south, except middle 50s near Lake MI.

Any light precipitation will come to an end Thursday night as the
shortwave trough pushes east. Another weak area of high pressure
is then forecast to move into WI later Thursday night and be
nearby on Friday. A return to sunshine and slightly warmer
temperatures aloft should bring max temperatures for Friday at
least close to normal levels for early May.

By the beginning of next weekend, the upper ridge is progged to
reach the eastern side of the Rockies/High Plains with building
upper heights across the central CONUS. Even though northeast WI
to still be in a northwest flow aloft, warming temperatures aloft
(8H temperatures in the +4 to +8C range) combined with sunshine on
Saturday, will bring surface temperatures to readings expected for
early May. This would translate to middle to upper 50s lakeside,
around 60 degrees north and lower to middle 60s south.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1245 PM CDT Sun Apr 30 2017

Conditions at midday ranged from VFR across much of northern
Wisconsin, to IFR generally from the Fox Valley east to Lake
Michigan. There was an area of MVFR ceilings in central Wisconsin.

Much of the rain moved out of the forecast area earlier but there
was still some leftover drizzle and fog. Rain was moving back into
the area early this afternoon ahead of approaching surface and mid
level systems, and conditions will likely deteriorate the rest of
the afternoon and this evening. Expect ifr ceilings during the
overnight hours on through Monday morning.
&&

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

$$

SYNOPSIS.......Skowronski
SHORT TERM.....Skowronski
LONG TERM......Kallas
AVIATION.......MG



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