Area Forecast Discussion
Issued by NWS Green Bay, WI
FXUS63 KGRB 211702
Area Forecast Discussion
National Weather Service Green Bay WI
1202 PM CDT TUE JUN 21 2016
Updated aviation portion for 18Z TAF issuance
.SHORT TERM...Today...Tonight...and Wednesday
Issued at 254 AM CDT Tue Jun 21 2016
Precipitation chances will be the focus today through Wednesday
in an increasingly active weather pattern.
The forecast area will remain in the northwest flow today into
this evening. With surface dewpoints in the 40s early this
morning...will continue with the dry forecast for most of the area.
A couple of subtle features could be enough to produce isolated
convection today over mainly the far northeast. An upper low
northeast of Great Lakes region will be close enough to the area
to sag a weak frontal boundary south into northern wisconsin.
Surface pressure falls also noted over northeast Wisconsin today
could be enough to pool any available moisture along a lake breeze
or the boundary. Steep low level lapse rates also noted. The ECMWF
and GFS do produce some light amounts today while the NAM is dry.
Tuesday night will be cool and quiet with the 850 ridge sliding
over. Precipitation chances will be on the increase over the
southwest half of the state late tonight as a warm front ahead of
a developing northern plains surface low and upper trough
approach the region. The llj with 850 front return to the area
late tonight with convection possibly reaching central Wisconsin
Convection will continue to spread northward Wednesday. Progs in
good agreement at this time with the surface frontal system
tracking south of the area starting Wednesday with the emphasis
of stronger to severe storms over southern Wisconsin. Best
instability also over southern wisconsin near the warm front and
points southward. Upper jet over the state providing healthy deep
layer shear even for central and east central wisconsin north of
the front. With pwats climbing to 1.50 inches...some locally heavy
rain possible even with storms north of the front.
.LONG TERM...Wednesday Night Through Monday
Issued at 254 AM CDT Tue Jun 21 2016
While a broad upper ridge continues to bake the southern CONUS
with record heat, the northern CONUS will see a strong band of
westerlies to persist through the upcoming weekend. One prominent
shortwave trough/associated cold front to be exiting the Great
Lakes Wednesday night with precipitation diminished by Thursday.
The next prominent shortwave trough (preceded by a cold front) is
expected to reach Southern Manitoba/Northern Plains on Sunday
before reaching Ontario/northern sections of the Great Lakes on
Mon. Look for warmer/more unsettled weather for the latter part of
Showers and thunderstorms look to continue through at least
Wednesday evening as a northern stream shortwave trough races from
the Upper MS Valley to the Great Lakes and an area of low pressure
tracks east along a warm front from the Midwest to southern
sections of the Great Lakes. Stronger instability appears to stay
just to our south where the warm front to initially reside, but
will need to carefully watch where the warm front to be located
because any shift north could place our southern counties in the
warm sector with much stronger instability and a higher risk of
severe storms. Precipitation chances are expected to slowly
diminish later Wednesday night as the surface low departs and
better forcing shifts east. Min temperatures to be in the lower to
middle 50s north, upper 50s to around 60 degrees south.
High pressure is expected to build into the Western Great Lakes
region on Thursday, bringing decreasing clouds, drier air and a
relatively light north wind (under 10 mph). Temperatures will be
seasonal with lakeshore areas in the lower 70s, mid to upper 70s
elsewhere. This high pressure pushes across the Great Lakes
Thursday night and heads toward the eastern Great Lakes on Friday.
Quiet conditions will prevail during this period with an uptick in
temperatures and dew points on Friday as winds turn to the south.
Max temperatures for Friday to range from the mid 70s near Lake
MI, to the lower to middle 80s over parts of central WI.
Onset of stronger WAA Friday night into Saturday could lead to a
gradual increase in showers/thunderstorms across the forecast
area. This activity will be spotty at best, thus there will be dry
hours even into Saturday afternoon. If clouds can stay away,
Saturday could also be the warmest (and most humid) day of the
extended forecast with max temperatures ranging from near 80
degrees near Lake MI, to the upper 80s over parts of central WI.
A better chance for a more widespread shower/thunderstorm event
will occur on Saturday night as a cold front drives east into WI
ahead of a shortwave trough pushing toward Lake Winnipeg. There
will be instability and plenty of moisture in place over WI when
the cold front arrives, however a late night arrival could limit
the strength of these storms. Just too early yet to get into
severe potential. Showers and thunderstorms are expected to carry
over into at least Sunday morning as the cold front pushes across
the rest of the WI. There is potential for a dry slot to rotate
into WI Sunday afternoon ahead of the shortwave trough/closed
upper low that is progged to reach extreme SW Ontario by 00z
Monday. Max temperatures on Sunday will be a bit cooler with lower
dew points as readings reach near 80 degrees lakeside, lower to
middle 80s elsewhere.
The shortwave trough/closed upper low is forecast to move E-NE
into southern Ontario Sunday night into Monday and may create
enough cyclonic flow to bring a small chance of showers mainly
to northern WI. Weak CAA rotating around the southern periphery of
this mid-level system will cool max temperatures on Monday to the
lower 70s north-central WI, mid to upper 70s south.
.AVIATION...for 18Z TAF Issuance
Issued at 1202 PM CDT Tue Jun 21 2016
VFR conditions through the taf period, but with
uncertainty increasing on Wednesday morning. Scattered to broken
cloud cover around 6-8 kft over north-central and far northeast WI
this afternoon may lead to a few sprinkles or light showers. These
clouds will dissipate/exit early this evening, leaving only
increasing mid and high clouds for the rest of the night. Then as a
warm front lifts into southwest Wisconsin on Wednesday, cloud bases
will be lowering with the potential for the northern extent of a
thunderstorm complex grazing central WI. Chances for thunderstorms
to be mainly south of a CWA to OSH line during the morning, then
increasing northward through the rest of the afternoon.