Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 180147 AAB

Area Forecast Discussion...UPDATED
National Weather Service Green Bay WI
847 PM CDT MON OCT 17 2016

New Information added to update section

Issued at 840 PM CDT Mon Oct 17 2016

The overall storm intensity has continued to decrease during the
past couple hours. Low-level flow continues to veer, so the severe
threat is just about over. The main band of thunderstorms tailed
back into the Rhinelander area, so most of the city received over
an inch of rain, with parts getting up to 3 inches. Reports
indicate some ponding of water, so although additional rainfalls
won`t be nearly as heavy, opted for a Flood Advisory to cover the
situation until the standing water recedes.

Some additional small cells have developed between AUW and GRB,
so will keep scattered-type PoPs going south of the main rain
band. Some new storms were developing back acrs MN as well, though
those seem likely to lift toward north-central Wisconsin.

Updated HWO (to remove the severe wording) will be out ASAP. Will
also make a determination on the need continuing the the Marine
Fog Advisory within the hour.

Issued at 717 PM CDT Mon Oct 17 2016

Frontal boundary has lifted northward some the past couple hours,
and now extends from near KTKV, eastward, to northern Marinette
county. Storms continued to peak in intensity near and just north
of the front. A few cell mergers likely resulted in the stronger
winds/wind damage over Oneida county about an hour ago.

Meso plots show the 850 mb flow has veered to the SW, though the
925 mb flow is still directed into the front. An overall decrease
in storm intensity has been noted in the past half hour, likely
related at least in part to weakening convergence near the front
due to the veering low-level flow.

Still need to closely monitor convective trends, especially since
small scale interactions such as mergers could lead to a
reintensification of some storms. But believe the overall
environment has started to become less favorable for strong

Given the overall storm movement to the east northeast, it is
possible the southern part of the forceast area may not see any
more showers/storms overnight. Pullled back PoPs over the far
south for the next couple hours, and may need to make further
adjustments a little later this evening if current trends

Issued at 512 PM CDT Mon Oct 17 2016

Convection, which appeared to initiate at middle levels, has
expanded in coverage during the past few hours. Large scale lift
was being aided by strengthening 925-850 mb flow which has backed
almost directly into the front. Across the forecast area, storms
seem to be peaking in intensity as they shift northward into the
frontal zone, then weakening as they head farther into the cooler
air mass.

Storms have thus far not shown sufficient organization to pose a
severe risk. But additional intensification is still possible
early this evening. The primary severe risk is of large hail,
though damaging wind gusts are possible near and south of the
front. Favorable large scale conditions for strong or severe
storms will probably persist for 3-4 more hours, then the flow in
the 850-925 mb layer is expected to rapidly veer to a more wswly
direction, greatly reducing convergence near the front, and likely
leading to a weakening of the convection.

.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 00Z TAF Issuance
Issued at 512 PM CDT Mon Oct 17 2016

Ceilings across the area were quite variable early this evening.
That will continue south of the front, though expect a more
uniform area of low ceilings (probably IFR or LIFR) to shift south
in the wake of the front. LLWS will also be an aviation concern
ahead of the front this evening.



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