Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 190430

Area Forecast Discussion
National Weather Service Green Bay WI
1130 PM CDT Sun Jun 18 2017

Updated aviation portion for 06Z TAF issuance

.SHORT TERM...Tonight and Monday
Issued at 236 PM CDT Sun Jun 18 2017

The latest rap analysis and satellite/radar imagery show low
pressure lifting northeast away from the region over eastern Upper
Michigan. Back edge of the comma head associated with this cyclone
has moved north of the U.P. border, but additional showers are
popping up beneath broader cyclonic flow aloft with help from a
minor instability. Still some time for a few thunderstorms to
develop this afternoon with surface based capes growing above 600
j/kg over central WI. With upper troughing firmly in place across
the region, precip trends and thunderstorm chances are the primary
concerns in the short term.

Tonight...Upper troughing will remain centered over the western
Great Lakes region.  Scattered showers and perhaps a thunderstorm
will linger into this evening, highest coverage across northern
WI. With loss of instability, should see shower coverage and
intensity diminish through the evening. Otherwise, clouds will
remain broken to overcast over northern WI tonight, while areas
over central and east-central WI should see more in the way of
breaks developing. Temps falling into the low 50s north to upper
50s near the Lake.

Monday...Models show a shortwave moving within the upper trough
and across the region during the afternoon. With daytime
instability, should see showers pop over central and north-central
WI by mid to late morning. Highest chances, however, will occur
over eastern WI where ml capes around 500 j/kg will be found
during the afternoon. Will continue the slight chance of a
thunderstorm in this area. Not expecting severe weather, though
any thunderstorms could contain small hail and brief gusty winds.
Highs remaining cool in the mid 60s to lower 70s.

.LONG TERM...Monday Night Through Sunday
Issued at 236 PM CDT Sun Jun 18 2017

Upper level flow will start off northwest Monday night then slowly
transition into a more zonal flow by Wednesday, with the zonal
flowing continuing into Saturday. Models show some differences
this weekend, as GFS/ECMWF turn the flow briefly to the southwest,
while the Canadian hangs on to more of a zonal flow. This is
mainly due to how deep the models dig a trough over the upper
Midwest. These differences should not have a huge impact on the
forecast but does increase uncertainty on how the precip chances
will play out.

A few chances for rain Monday night into Tuesday as weak pieces
of energy move across the area within the northwest flow, but
models have backed off a little on how widespread the shower/storm
chances will be. Will continue to carry low chances for precip,
but thinking much of the time will end of being dry. Brief ridging
moves across the state Tuesday night into Wednesday morning, so
will continue with a dry forecast. The ridge will quickly shift
east as a low pressure system crosses southern Canada, with
associated warm/cold front. These boundaries, along with a push of
warm air advection ahead of the system, looks to be the focus of
one or two areas of showers and storms, all shown by the
GFS/ECMWF/Canadian. Will introduce likely POPs for much of the
area Wednesday evening as models are converging on this period for
the best chance for widespread precip.

The cold front should make it far enough south of the area on
Thursday to keep most shower/storm activity across southern WI,
but can`t completely rule out a shower or storm across central and
east central WI, especially in the afternoon and evening if the
front gets hung up and as a shortwave trough approaches from the
northwest. Models not in the best agreement with this shortwave so
will see how things pan out. Model disagreement continues into
the rest of the long term, as flow becomes northwest again and
timing/location differences of shortwave troughs will need to be
sorted out before any real clarity on when the best chances for
precip will be.

Temperatures will start off below normal within the northwest
flow, climb to near or above normal on Thursday as the area
briefly gets into the warm sector, then settle back below normal
for the end of the week as the warm/hot air gets pushed well to
our south.

.AVIATION...for 06Z TAF Issuance
Issued at 1129 PM CDT Sun Jun 18 2017

A broad upper trough will remain across the area the next couple
days. The overall trend has been for clouds and showers to
dissipate since sunset, but there are still plenty of patches of
clouds around. An increase in clouds and showers is expected
again by mid-late morning tomorrow as daytime heating occurs.



LONG TERM......Bersch
AVIATION.......Skowronski is the U.S. government's official web portal to all federal, state and local government web resources and services.