Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 191805
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
105 PM CDT FRI AUG 19 2016

Updated aviation portion for 18Z TAF issuance

.SHORT TERM...Today...Tonight...and Saturday
Issued at 356 AM CDT Fri Aug 19 2016

Doppler Radar trends show a thunderstorm complex currently
developing across the upper Mississippi Valley, tracking east
towards Wisconsin early this morning. Hi-res model runs weaken
this system quite a bit by the time it rolls through the cwa later
this morning which makes sense given MUCAPE values drop off
precipitously as you head east into the cwa. Therefore the
upstream severe weather is not expected to make it into the area,
with only a heavy rain threat lingering as this complex tracks
across northeast Wisconsin.

Later today and into tonight the models regenerate showers and
thunderstorms as a shortwave tracks through the western Great
Lakes region this afternoon and this evening. However the most
unstable air will remain south of the cwa as this mornings
convection prevents much in the way of recovery across northeast
Wisconsin given the cloud cover afforded by the expansive shield
of clouds moving into the area from the west, which is not
expected to dissipate much during the afternoon hours. Although
there could be a pulse storm that produces near or severe
weather, the severe weather threat today and tonight does not
appear to be all that impressive. That being said long skinny
cape profiles, a rather weak wind field, pwat values approaching
2 inches and training of thunderstorm development could lead to
localized flooding today and tonight as these showers and
thunderstorms develop.

The forecast becomes rather murky on Saturday as vastly different
model solutions emerge regarding the low pressure system tracking
through the western Great Lakes region. The NAM model seems to be
the outlier, producing a closed off mid fall type cyclone that
deepens and slowly tracks through the region during the weekend.
While the Canadian seems to also hint at this solution, the ECMWF
and GFS are more progressive and not as deep as the NAM solution.
Given the out of season look to this system will side with the
solutions that do not look like a fall cyclone this run. The
severe weather threat appears to be more of a concern Saturday as
an area of 2000 J/kg of MUCAPE sneaks into the eastern cwa ahead
of the cold front sweeping through the cwa. Although the window is
brief, instability does suggest a marginal threat for severe
weather across east central and portions of northeast Wisconsin on
Saturday depending on how much instability can be realized ahead
of the cold front and the timing of the front itself. Wind damage
appears to be the main threat, with marginally severe hail a
secondary threat on Saturday.

.LONG TERM...Saturday Night Through Thursday
Issued at 356 AM CDT Fri Aug 19 2016

00Z model differences were already apparent at the start of this
forecast period. The NAM and Canadian both kept rain around
longer than the GFS and ECMWF, and had higher totals across most
of the forecast area. Have sided with the faster solutions and
went with no higher than slight chance POPs by Sunday afternoon,
then dry for Sunday night. Models seemed to have the same general
idea of a weak mid level ridge over the central CONUS early in the
week moving into the Great Lakes region by midweek. They develop
QPF with some short wave energy ahead of an approaching surface
system but timing and location are different. Thus, confidence is
low in the precipitation chances Tuesday night through Thursday.

Below normal temperatures are expected on Sunday behind the
departing surface system, but surface high pressure followed by
return flow will bring high temperatures near normal for Monday
and well above normal again starting Tuesday.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 104 PM CDT Fri Aug 19 2016

Look for showers to continue to push across northern WI this
afternoon as a frontal boundary approaches from the NW. A few
showers could push into central and east-central WI as well. An
isolated storm is also possible. The boundary is forecast to sag
south across the area this evening without much fanfare. Can`t
rule out a few showers or a storm, but coverage/duration should be
on the low side. The shower and storm threat ramps up after
midnight and especially early Saturday morning as low pressure
approaches from the SW and a deep upper level system pushes in
from the west. Look for very poor flying conditions for much of
Saturday as widespread showers and fog is expected along with the
chance for storms.
&&

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

$$

SHORT TERM.....Kurimski
LONG TERM......MG
AVIATION.......Bersch



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