Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 171724
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1224 PM CDT Wed May 17 2017

Updated aviation portion for 18Z TAF issuance

.SHORT TERM...Today...Tonight...and Thursday
Issued at 410 AM CDT Wed May 17 2017

Looks like another day of severe thunderstorms is likely. An
unseasonably strong negatively tilted upper low lifting northeast
from the Central Plains will provide considerable upper support
for severe storms this afternoon and evening, while a slow moving
cold front, outflow boundaries and perhaps lake and bay breezes
provide for surface convective initiation. Cloud cover will hinder
solar heating and surface based instability for a good part of
the day, but there should be a least some breaks in the clouds in
the warm sector over the southeast half of the forecast region
later today.

The Saint louis University web page of forecast analogs showed
that nearly all of the top analogs were associated with severe
weather somewhere in Wisconsin and nearly half with tornadoes.
The NWS western region web page that displays return intervals of
various surface and upper air parameters show that the intensity
of the upper system has a return interval of once every 2 or 3
years in Wisconsin and is outside of the climatological database
in Iowa. So this will probably be an active day of severe storms
over parts of the Midwest and western Great lakes.

Clouds and showers and thunderstorms will keep temperatures in the
60s in far northern Wisconsin. The concentration of storms along
the front has the potential for producing heavy rain and local
flooding. Further south and east there will probably be just
isolated or scattered storms until late afternoon or evening as
the upper system gets closer and the surface cold front starts to
move east. The combination of best instability and shear averages
out to be somewhere between Wausau and Menominee County Michigan
late in the afternoon and early evening, with energy helicity
indices of around 3.

The storms will move across the area tonight and exit early
Thursday as the cold front moves through. Heavy rain will be the
main concern once the severe threat has ended. The air is cold
enough behind the front for temperatures to actually fall during
the day, something rare for this time of the year.

.LONG TERM...Thursday Night Through Tuesday
Issued at 410 AM CDT Wed May 17 2017

Models start this part of the forecast dry, with surface high
pressure and a mid level ridge across region. Precipitation is
then expected to move in late Friday night as a mid level trough
and surface low move northeast toward the region. PoPs drop to
slight chance on Sunday in the dry slot of the system. The
unsettled weather pattern continues into early next week as
another shortwave trough and cold front move into the Great Lakes
around Tuesday.

High temperatures are expected to be below normal through the
middle of next week.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1223 PM CDT Wed May 17 2017

Several rounds of showers and thunderstorms will impact the TAF
sites during the TAF period. The best chance for thunderstorms
will be this afternoon and early this evening, with lower chances
later tonight into Thursday morning. CIGS have settled between low
VFR and MVFR this afternoon, with bases basically between 2500 and
3500 ft. Conditions will drop with showers and thunderstorms to a
solid MVFR/IFR deck, with lower conditions possible with heavier
rain activity. A cold front will move through Thursday morning,
bringing additional showers and low clouds. Conditions are not
expected to improve appreciably until Thursday afternoon when the
main low tracks east.
&&

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

$$

SHORT TERM.....RDM
LONG TERM......MG
AVIATION.......Kurimski



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