Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 172016

Area Forecast Discussion
National Weather Service Green Bay WI
316 PM CDT MON OCT 17 2016

Forecast discussion for routine afternoon forecast issuance

.SHORT TERM...Tonight and Tuesday
Issued at 316 PM CDT Mon Oct 17 2016

The main concerns in the short term are thunderstorm chances and
their severe potential.

Surface analysis at 19z showed a warm front to the northeast of
the forecast area and a cold front across western Vilas County.
The airmass in the warm sector of the surface system, that
covered almost the entire area early this afternoon, was quite
warm and humid. Temperatures reached the upper 60s and 70s,
except in the far north where fog and low clouds suppressed
daytime heating, and dew points were in the 60s. The 12Z GRB
sounding showed saturated conditions below a strong inversion just
below 700mb. MU CAPE values were in excess of 1000 j/kg over most
of the area throughout the day, but there was enough CIN to keep a
lid on things. 19Z mesoanalysis graphics indicated that the cap
was eroding across central and east central Wisconsin, and in
southeast Minnesota and western Wisconsin where an areas of showers
developed after 18Z.

Models had a 850mb low passing across northwest Wisconsin this
evening and a surface low moving across west central and northeast
Wisconsin ahead of an approaching mid level trough. Northern
Wisconsin was forecast to be in the left exit region of an upper
jet max as well, so that is the area of greatest concern for
severe storms tonight. SPC day 1 outlook had a slight risk
generally north of Highway 29. In addition, significant deep layer
shear across the north in the presence of a surface boundary
brings the potential for supercell development.

PWAT values were at least an inch, 1.51 at GRB, this morning so
heavy rainfall is also a concern. Dense fog is possible overnight.
Expect cooler day on Tuesday but highs are still forecast to be at
least 5F above normal.

.LONG TERM...Tuesday Night Through Monday
Issued at 316 PM CDT Mon Oct 17 2016

For the rest of the work week, a series of short wave troughs
with cold frontal passages in the west to northwest flow will
bring in a cooler and drier air mass. little or no precipitation
is expected.

One front is progged to pass through late Wednesday into
Wednesday night and then another cold front with greater height
falls aloft for Friday. Could be cold enough for a light mix
across the far north toward Thursday into Friday as 850 mb temps
fall to -4 C. Frost freeze headlines may be required later this
week for the lingering growing areas over central and east central

Continued west to northwest flow aloft after Friday will bring a
couple of fast moving weak frontal systems over the area this
weekend and early next week. Medium range model timing divert this
weekend with the strength of a plains surface ridge which would play
a role on small precipitation chances as well as temperature

.AVIATION...for 18Z TAF Issuance
Issued at 102 PM CDT Mon Oct 17 2016

MVFR conditions prevailed across most of the forecast area at
midday, with mainly IFR ceilings and fog across north central
Wisconsin. The entire forecast area was in the warm sector of a
surface system. There was a surface inversion evident on the 12Z
GRB sounding and the atmosphere was saturated below a stronger
inversion just below 700mb. Mesoanalysis showed SB CAPEs in excess
of 1000 j/kg across much of the area at 17Z but there was still
plenty of CIN.

Little or no improvement is expected the rest of the day and the
chance for thunderstorms increases later this afternoon with an
approaching jet max and mid level short wave, and a surface low
over the Plains moving northeast along the cold front. Showers and
storms should exit the area late tonight but some low clouds and
fog may hang around for a while. VFR conditions should prevail on



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