Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 222336

Area Forecast Discussion
National Weather Service Green Bay WI
636 PM CDT Tue Jun 22 2021

Updated aviation portion for 00Z TAF issuance

Issued at 350 PM CDT Tue Jun 22 2021

Turning warmer and more humid with showers and thunderstorms at
times during the latter half of the work week.

The upper flow across North America will flatten the next couple
days, then reamplify. The main westerlies will reestablish across
central and northern Canada during the latter part of the period,
leaving a weaker but highly amplified secondary branch of the
flow across the CONUS and southern Canada.

Temperatures will warm to near/slightly above normal levels
tomorrow and remain there for the rest of the period. It will
also be somewhat humid at times, especially late this week. A slow
moving frontal system will cross the area late this week, likely
resulting in AOA normal precipitation.

.SHORT TERM...Tonight and Wednesday
Issued at 350 PM CDT Tue Jun 22 2021

The convection over northeast Wisconsin was diminishing, and
should continue to do so as large scale forcing favors descent and
the jet axis/cold pool aloft slides off to the east. Clouds will
decrease this evening, but should increase late tonight as a weak
mid-level shortwave approaches and weak isentropic lift at low-
levels spreads across the area. Support for precipitation across
C/E-C WI late tonight into Wednesday didn`t look as favorable as
it did previously. Maintained some slight chance PoPs--mainly in
E-C WI. But coverage of any convection would be limited, and it`s
even questionable if it would be accompanied by thunder.

Stayed fairly close to the NBM which has been verifying pretty
well lately.

South winds flowing up the length of Lake Michigan will result in
building waves Wednesday. Hazardous swimming conditions are also
likely at Lake Michigan beaches.

.LONG TERM...Wednesday Night Through Tuesday
Issued at 350 PM CDT Tue Jun 22 2021

Zonal flow over the northern Plains and western Great Lakes mid-
week will amplify late in the week as the strong western ridge
builds and an upper trough sets up shop over the central CONUS. As
this transition takes place, there will be several periods with
rain/storms chances, but plenty of details still to be worked out
as models continue to differ on how things will play out. Heavy
rain/severe threat will need to be monitored on Thursday into
Friday. Temps look to stay close to or slightly below normal with
humidity levels peaking Thursday/Friday.

Wednesday night into Thursday night...warm front will be pushing
into/across the area Wednesday night, with embedded shortwaves
riding the zonal flow through the period. These, in combination
with pushes of WAA and an approaching cold front, will keep high
chance or likely PoPs in the forecast as at least one or two
rounds of convection are likely, but doubt it will actually rain
each period. Models showing PWATs approaching 2.25" ahead of the
cold front. This would lead to an obvious heavy rain threat,
especially with any training or back-building convection. NAM/GFS
have some beefy 3-5+" totals but other models not as aggressive.
Still some concern upstream convection could disrupt moisture
transport into the area. The severe weather threat looks to be
greatest to our south/west, but depending on how things play out,
bulk shear of 30+ knots would support some organized convection.
Debris clouds and upstream convection could keep instability in
check though. In addition, some convective feedback could be
contaminating some of the model output. So plenty of details to
still pin down at this point. Both nights are looking mild with
lows mainly in the 60s. Highs will be highly dependent on how the
surface features and convection pan out. It will be a fairly muggy
period, but just how muggy will be dependent on how much low
level moisture advection can occur and if dewpoints can creep
toward the 70F mark.

Friday...lingering convection could be ongoing during the morning
(or afternoon?) hours depending on how things pan out Thursday
night, especially across the south/east. If the surface wave is
slower and farther north, a more widespread precip event would be
likely. Heavy rain and some flooding would be the main concern if
this were to occur as PWATs remain near 2". It looks to be a
little cooler than Thursday due to the cloud cover and/or being
behind the front.

Rest of the long term...the upper trough will park itself over the
northern Plains and western Great Lakes. Less humid air is
expected to filter into the area, but chances for showers and
storms will likely continue at times as shortwaves will rotate
around/through the trough. Way to early to try to time these out,
so chance PoPs litter the forecast. Temps will fall back to near
or slightly below normal.

.AVIATION...for 00Z TAF Issuance
Issued at 636 PM CDT Tue Jun 22 2021

Showers and sprinkles across the far north will continue to
dissipate this evening with the loss of daytime heating. Otherwise
VFR ceilings are expected overnight with mostly clear skies. MOS
guidance continues to be bullish on producing an MVFR cloud deck
during the morning hours on Wednesday across central and east-
central Wisconsin. Given the continuity between the models and
between runs will lower cigs across all airports save for KRHI
with this issuance. The models do dissipate this deck by Wednesday
afternoon, with VFR conditions across all TAF sites. There is a
slight chance for showers and thunderstorms across central through
northeast Wisconsin on Wednesday as a weak shortwave tracks
through southern Wisconsin; however, coverage and confidence is
low enough to leave out of the TAF sites with this issuance.



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