Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 152023

Area Forecast Discussion
National Weather Service Green Bay WI
323 PM CDT SAT OCT 15 2016

Forecast discussion for routine afternoon forecast issuance

.SHORT TERM...Tonight and Sunday
Issued at 322 PM CDT Sat Oct 15 2016

Rain, thunder and fog potential through Sunday morning are the
main concerns during this part of the forecast.

Southerly flow ahead of an approaching cold front brought upper
50s and lower 60s dew points to much of the area today. Morning
soundings from around the area showed low level moisture trapped
below a strong inversion. This resulted in overcast conditions
that kept temperatures from getting any warmer than the lower to
middle 60s and also brought areas of light drizzle and fog to
north central Wisconsin for much of the day. Guidance was showing
large areas of small QPF across the area for the afternoon but
will probably take a while for any rain to saturate the dry layer
between about 850mb and 600mb that was evident on 12Z soundings.

The approaching cold front and a mid level short-wave trough will
bring a better chance for showers to the area during the evening.
Mid level lapse rates were at least 7C/km across the entire
forecast area. Even so, have kept pops in the chance category but
did keep a mention of thunder.

Once the front has passed, skies should start to clear and winds
are expected to decrease. MOS guidance was indicating dense fog
with lingering moisture in the area. Have areas of fog with patchy
dense fog mentioned for most of the area overnight to cover this
for now.

.LONG TERM...Sunday Night Through Saturday
Issued at 322 PM CDT Sat Oct 15 2016

Nearly zonal flow across the Great Lakes Region will provide an
active pattern through the early part of the new work week. Main
energy in this westerly flow impacting the U.S. northwest coast
before tracking across Canada. A frontal boundary from this
weekends system, which shifted south of the area, will lift back
northward Sunday night as a warm front for a return of showers and
storms across the area. Instability and moisture will return
quickly due to a southerly 40 knot low level Jet and proximity.
SPC has placed much of Northwest Wisconsin in a marginal risk for
Sunday afternoon and night as the nose of strong upper jet works
into the area.

Progs in agreement with the front may stall across the northern
Great Lakes Region on Monday as 850 MB winds remain from the
southwest. A piece of energy originating from the west coast
slides over Monday night.

MU capes increase to around 1000 J/kg Sunday night and continue
into Monday night depending on the model. Total totals climb into
the lower to mid 50s during this period as well. Potential for
strong to isolated severe storms possible when combining this
instability with the deep layer shear as a 130 knot upper jet
works into northwest Wisconsin by Monday afternoon. Will need to
watch later trends this weekend.

After this short wave trough slides to the northeast Tuesday
morning, will add some resolution and diminish pops later Tuesday
as the surface cold front slides southeast of the area. Northwest
flow Tuesday night into Wednesday will allow a gradually cooler
air mass to near normal temperatures to drop in. Medium range
progs in good agreement with convection along the boundary to
remain south of the area Wednesday.

Periods of clouds along with small chances of precipitation
possible the later half of the week as an upper low or deep
trough develops over the Great Lakes in response to the Western
states upper ridge. Any precipitation which can develop may be
more diurnally driven as 850 temps fall to around -4 C by Thursday
night and a surface to 850 ridge nudges into western wisconsin.
Cyclonic flow, especially at the boundary layer with the deeper
moisture appears to be southeast of the area toward the Ohio
Valley, but may be close enough to brush areas near the lake
shore at times.

.AVIATION...for 18Z TAF Issuance
Issued at 1258 PM CDT Sat Oct 15 2016

A mix of MVFR and IFR conditions prevailed across the forecast
area at midday, with cigs mainly in the 500-1500ft range and some
fog and/or drizzle reducing visibilities to 1-3SM. Expect little
or no improvement as rain chances increase ahead of an approaching
cold front. Would not rule out the possibility of some thunder but
chances are too low to include in TAFs. Rain chances should come
to an end as the front passes, but decreasing winds and at least
partial clearing will result in MVFR/IFR fog development later
tonight. Fog is expected to dissipate during the morning hours on
Sunday, resulting in VFR conditions.



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