Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 121148
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
648 AM CDT Sun Jul 12 2020

Updated aviation portion for 12Z TAF issuance

.SHORT TERM...Today...Tonight...and Monday
Issued at 313 AM CDT Sun Jul 12 2020

The passage of a back door cold front and upper trof brought some
clouds and a few showers to eastern WI overnight, but the showers
had since moved out over Lake Michigan. Winds increased in the
Fox Valley and lakeshore areas in the wake of the frontal passage,
with gusts to 20 to 25 mph occurring for a few hours.

Canadian high pressure will build into the region today. With a
cooler air mass arriving, conditions will be more favorable for
diurnal cumulus development, so partly to mostly cloudy skies are
anticipated in the late morning and afternoon. Weak instability
over central WI may lead to a stray shower or two later in the
afternoon, but the probability of occurrence is too low to mention
at this time. High temperatures will be in the 75 to 80 range.

The high will remain over the region tonight, leading to comfortable
lows in the upper 40s and 50s in most places. Clear skies and
light winds should result in patchy fog development overnight.
Fog will be most likely in the favored locations of north central
WI.

The high will drift slowly east on Monday, allowing light south
winds to develop. Temperatures will be a few degrees warmer, in
the upper 70s and lower 80s. Dry conditions are expected, along
with partly cloudy skies.

.LONG TERM...Monday Night Through Saturday
Issued at 313 AM CDT Sun Jul 12 2020

Typical summer pattern shaping up across the CONUS this week with
a sprawling subtropical upper high over the southern CONUS and the
main band of westerlies running over southern Canada/northern tier
of states. A broad mid-level shortwave trough is forecast to move
across the northern CONUS, reaching the Great Lakes Tuesday night
into Wednesday accompanied by a cold front. Depending on how far
south this front can move before stalling, precipitation may
linger into Wednesday night. Models differ late week with the
location of the upper high and the possible passage of another
shortwave trough. Temperatures to be at or above normal this week
with hot/humid conditions possible next weekend if the upper high
can lift north.

Clouds will gradually be on the increase Monday night as a cold
front moves into the Upper MS Valley. The leading edge of showers/
thunderstorms will impinge upon north-central WI toward daybreak,
thus have carried chance pops per previous forecast. Min
temperatures to be in the upper 50s to around 60 degrees north,
lower to middle 60s south. This cold front is forecast to be a
slow-mover due to a blocking upper trough over the New England
states. Models only have the front reaching central WI by 00Z
Wednesday with better upper support provided by an embedded
shortwave within the broad mid-level shortwave trough centered
over the northern Plains. Instability remains somewhat marginal
with MUCAPES in the 1000-1500 J/KG range, however the 0-6km shear
does reach 30-35 knots by Tuesday afternoon, thus stronger storms
will be possible. PW values climb into the 1.5-2.0" range along
the cold front, therefore another round of heavy rain may occur.
Max temperatures Tuesday to range from the middle 70s north-
central WI, lower to middle 80s eastern WI.

The front creeps into eastern WI Tuesday night with the emphasis
for showers/thunderstorms and heavy rain potential following suit.
The precipitation should begin to taper off over north-central WI
after midnight as better lift/forcing shift east. Cannot rule out
a few stronger storms into the evening hours, but weakening
instability should limit any severe potential. Min temperatures to
range from the middle to upper 50s north-central, to the middle
60s east-central WI. As the cold front slowly moves to our east on
Wednesday, models indicate a surface wave will move northeast
along the boundary. The region will also be in the right entrance
region of the upper jet for added lift. East-central WI would be
most vulnerable for additional showers/thunderstorms, thus highest
pops placed there. Still do not see much in the way for
precipitation over north-central WI and may trim or remove pops.
Max temperatures to mainly be in the upper 70s to lower 80s.

Precipitation could linger over east-central WI into Wednesday
evening before ending as the surface wave departs the area. The
rest of Wednesday night will see weak high pressure build into WI,
bringing a decrease in clouds and light winds. This high pressure
to spread across the Great Lakes region on Thursday with partly
cloudy skies and max temperatures in the lower to middle 80s.

The next chance for showers/thunderstorms looks to arrive Friday
afternoon into at least central WI as another weak ripple moves
through the westerlies and a surge of warmer air approaches WI.
Have kept pops low for now with max temperatures on Friday warming
into the middle to upper 80s.

A better chance of showers/storms would appear to be late Friday
night into Saturday a a cold front pushes into WI and runs into a
very warm/moist air mass. Depending on the timing of the front
across the forecast area, some of these storms could be on the
strong side with MUCAPES greater than 2000 J/KG. Much too early to
speculate on severe at this point, just something to watch as we
get closer to next weekend. Max temperatures for Saturday should
again be mainly in the middle to upper 80s with dew points in the
middle 60s to around 70 degrees.
&&

.AVIATION...for 12Z TAF Issuance
Issued at 638 AM CDT Sun Jul 12 2020

Lake-enhanced clouds dropping south through far northeast WI could
bring a period of MVFR flight conditions to the eastern TAF sites
this morning, otherwise expect SCT-BKN cumulus clouds to form with
the heating of the day. These clouds should dissipate after
sunset. Mostly clear skies and light winds should result in fog
formation late tonight, with the best likelihood over north central
WI, including the RHI TAF site.

&&

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

$$

SHORT TERM.....Kieckbusch
LONG TERM......Kallas
AVIATION.......Kieckbusch



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