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Area forecast discussion 
National Weather Service Green Bay WI
605 am CDT Wednesday Aug 27 2014

Updated aviation portion for 12z taf issuance

Short Thursday
issued at 206 am CDT Wednesday Aug 27 2014

Upper short wave passing over the area producing bands of showers
across far eastern Minnesota into the north half of Wisconsin.
Will adjust showers coverage to scattered to parts of the area as
per area radars. Early estimate of the timing of the back edge of
the showers and also the short wave axis reaches the grb area
around 12z. As a result may need to hang onto a shower mention for
a few hours this morning for locations east of the Fox River and
Lake Winnebago.

After a period of clouds this morning...anticipate clearing skies
this afternoon and into tonight as the surface high pressure
reasserts itself again under building upper heights. Fog is likely
back in the picture with the clearing skies and light winds.

Clouds to be in the increase from southwest to northeast on
Thursday with the return of a warm front and increasing precipitable waters from
the deep moisture source over the middle miss region. Models in good
agreement with rain spreading back into central Wisconsin
starting late morning or early afternoon.

Near normal temperatures expected today followed with a little cooler
temperatures on Thursday with the increasing clouds.

Long term...Thursday night through Tuesday
issued at 206 am CDT Wednesday Aug 27 2014

The latest GFS ensemble mean indicates that the pattern will start
out as split flow before transitioning to a large trough over
western North America and a ridge across the east. The medium range
models are on board with this pattern...but offer some differences
in the details. The GFS is quicker and farther east ejecting a
southern stream upper low across the western Great Lakes compared to
the European model (ecmwf) this weekend. Most of the guidance sides with the GFS and
will side that direction unless the 00z model runs make a drastic
change. The European model (ecmwf) will work for later periods though.

Thursday night through Friday night...weak shortwave troughing will
be moving through Thursday night and promote a warm front lifting
northeast across the state. Good forcing along the warm front in
the form of upper divergence in the right rear quadrant of a jet streak
and fgen along the nose of a modest 30 knots low level jet will provide the focus
for a possible mesoscale convective system. Elevated instability is noticeably absent
however...and can only find a 200-400 j/kg on BUFKIT soundings. But
even though severe weather is unlikely...precipitable waters will be reaching
slightly above 2 inches making heavy rainfall the main threat. Both
the European model (ecmwf) and GFS track a possible mesoscale convective system across central to northeast
Wisconsin. The 850mb warm front will clear Door County Friday
morning but the tropical moisture plume will hang around over
east-central and northeast Wisconsin. Wouldnt be surprised to see a
break in the precipitation behind the mesoscale convective system Friday morning...and then
redevelopment late Friday afternoon into Friday night. No
significant changes to temperatures.

Rest of the forecast...a southern stream short wave and associated
surface low will then be lifting across the region on Saturday
before departing Saturday night. With precipitable waters continuing to remain
near 2 inches over eastern Wisconsin...rounds of heavy rainfall
appear possible. A dry period could then follow Sunday into the
first half of Monday. Then the next cold front arrives later Monday
into Monday night as the flow turns southwest ahead of the western noam

Aviation...for 12z taf issuance
issued at 526 am CDT Wednesday Aug 27 2014

Isolated to scattered light showers were falling out of a VFR or
middle level cloud deck this morning as a short wave trough tracks
over the western Great Lakes region. Mainly VFR conditions are
then expected for the rest of today into tonight. Patchy MVFR or
IFR visibilities due to fog may develop across the north late tonight.

issued at 206 am CDT Wednesday Aug 27 2014

Developing southwest flow aloft this week will allow a very moist
air mass to spread back into the Great Lakes region. Precipitable waters ranging
from 1.5 to 2.00 inches working into the area later Thursday and
continuing into Saturday with the higher readings over south half
of the state. H850 front lifting north later Thursday into
Thursday night will support the first round of heavy rain while a
second round of heavy rain tied to a 850 low along with a bit more
upper jet support to produce another round of heavy rain.
Potential of 1 to 2 inches with both events...and quite possible
total rainfall amounts from the period Thursday afternoon to
Saturday evening could range from 1.5 inches to nearly 4 inches.
Even though its possible a break will occur between these events
and river levels are near normal as of Wednesday...will issue an
esf for rising rivers and the potential of training storms along
the front which could produce locally higher amounts. Its also
possible a watch would be needed after the first event saturates
the ground.

Grb watches/warnings/advisories...


Short term.....Tdh
long term......mpc

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