Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 301127
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
627 AM CDT MON MAY 30 2016

Updated aviation portion for 12Z TAF issuance

.SHORT TERM...Today...Tonight...and Tuesday
Issued at 359 AM CDT Mon May 30 2016

Satellite showed a s/w trof moving through eastern WI early this
morning, but isold showers associated with this feature had
recently dissipated. At the surface, a weak ridge of high pressure
was building into nc/c WI, and causing patchy fog to develop
there. The sfc ridge will bring mostly sunny skies and pleasant
weather for Memorial Day, with high temperatures ranging from the
middle 70s to lower 80s.

After a generally dry evening, showers and a few tstms will
gradually spread northeast across the forecast area overnight.
Far eastern WI is expected to remain dry through the night. The
pcpn will develop in response to the arrival of an 850 mb warm
front and associated waa and moisture convergence.

A surface warm front will lift north into the forecast area on
Tuesday. Increasing south winds will bring a very moist air mass
back into the region, with PWATs increasing to 1.5 inches in
central WI, and H8 dew points climbing to +10 to +12 C. A couple
s/w trofs will clip through our northwest counties, so the highest
pops and QPF will likely occur there. Aside from a heavy rainfall
threat, there is at least a marginal risk of severe tstms, as CAPE
is expected to increase to 1000-1500 j/kg by afternoon. The best
bet will be along and just north of the warm front, where 0-3 km
helicities may be as high as 200-300. SPC has outlooked the
northwest two-thirds of GRB CWA in a marginal risk, and this seems
reasonable. High temperatures should be in the 70s to around 80
range.

.LONG TERM...Tuesday Night Through Sunday
Issued at 359 AM CDT Mon May 30 2016

Little change indicated by the models with respect to the mean
flow across the CONUS through next weekend. A prominent upper
ridge will be located over the Western Atlantic, while a new upper
ridge develops over the Western CONUS later this week. The main
weather featureof interest for NE WI to be the eastward movement
of a shortwave trough across the northern tier of states during
the Tuesday-Thursday time period. This trough (and its associated
cold front), will bring another period of unsettled weather back
to WI through mid-week before the mean flow turns NW and more
seasonal conditions to return. There are some questions with
regards to a possible weak system next weekend that will need to
be addressed.

The shortwave trough is expected to move from the Northern Plains
into the Upper MS Valley Tuesday night, while a modest cold front
pushes eastward toward western WI toward daybreak. A broad
southerly flow into WI will pull plenty of gulf moisture northward
with dew points climbing through the 50`s and PW values hovering
around 1.5". Even though instability will be weakening through the
night, there will be plenty of lift available between the
approaching cold front and diffluent flow aloft to compensate with
with enough shear present (around 30 knots), expect to see a band
of showers and thunderstorms to move into the forecast area. A few
of these storms may be strong into Tuesday evening (before
instability weakens), otherwise potentially heavy rain looks to be
the main threat for Tuesday night. Min temperatures are expected
to settle into the mid to upper 50`s north, upper 50`s to around
60 degrees south.

Showers/thunderstorms should continue through at least Wednesday
morning as the cold front moves through the rest of the Badger
state. The shortwave trough lags behind over the Upper MS Valley
with the models showing a dry slot to rotate through the Western
Great Lakes during the afternoon. If this were to occur,
precipitation chances would diminish especially over central WI
who would be farthest away from the exiting cold front. Max
temperatures on Wednesday to range from the upper 60`s to around
70s degrees near Lake MI, to the mid to upper 70`s across
central/ east-central WI.

The shortwave trough finally reaches the Western Great Lakes
Wednesday night, but in a weakened fashion. The cold front to be
long gone and with the deepest low-level moisture well to our
east, there is not much lift or moisture left for the shortwave
trough to use for further precipitation development. Furthermore,
drier air is expected to overspread WI through the night, thereby
limiting precipitation chances even more. A stray showers or a few
sprinkles may develop on Thursday as cooler air aloft increases
mid-level lapse rates. That being said, it is looking more like
the vast majority of the region will remain dry Thursday with weak
high pressure building across WI. Max temperatures on Thursday
could drop a bit below normal with mid 60`s north-central WI, to
the lower 70`s eastern WI (cooler lakeside).

After a quiet Thursday night with the high pressure overhead,
attention turns to a weak system expected to drop southeast
through the new northwest flow aloft on Friday. Both the GFS and
GEM have sped up this system toward wI with a shortwave trough
pushing into the Upper MS Valley and a pretty good surge of
isentropic lift into wi by Friday afternoon. The ECMWF is not as
ambitious and holds any precipitation off through the daylight
hours. May need to at least increase clouds and perhaps add a
small pop to the forecast. Max temperatures Friday will continue
to run a bit below normal with mid 60`s lakeside, upper 60`s north
and lower 70`s south.

Models continue to struggle with the handling of not only this
first system dropping southeast through the region, but also a
subsequent system toward the latter part of the weekend. This is
typical of the models when the mean flow undergoes a major change
and anticipate the models will continue to struggle with these
weak systems for a few more days to come. This all leads to great
uncertainty as to when to add pops to the forecast from Friday,
right on through Sunday. Due to this uncertainty, have leaned on
the consensus solution which now has at least slight chance pops
from Friday night through Sunday. Temperatures are forecast to
remain at or slightly below normal through next weekend.
&&

.AVIATION...for 12Z TAF Issuance
Issued at 621 AM CDT Mon May 30 2016

Patchy fog will quickly dissipate early this morning, followed by
prevailing VFR conditions for the majority of the TAF period.
Showers and isold tstms will develop in central WI toward midnight
tonight, then gradually spread northeast overnight. Local MVFR
conditions may accompany the showers in central WI late tonight.
Will not add any tstms to the TAFs right now, as instability will
be fairly weak and confidence in the occurrence of tstms at any
given site is too low.

&&

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

$$

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


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