Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 291940
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
240 PM CDT WED JUN 29 2016

Forecast discussion for routine afternoon forecast issuance

.SHORT TERM...Tonight and Thursday
Issued at 240 PM CDT Wed Jun 29 2016

Main forecast emphasis to be placed on convective potential on
Thursday as a cold front/mid-level shortwave trough system sweeps
through the region. Potential for marginal severe storms remains
in play, mainly during Thursday afternoon for most of NE WI.

The 19z MSAS surface analysis indicated an area of high pressure
over the western half of the Great Lakes. A cold front extended
from near Hudson Bay southwest through western Ontario into
eastern North Dakota. Radar mosaic showed a line of thunderstorms
in the vicinity of this cold front. For NE WI, visible satellite
imagery only showed a high-based cu field and high clouds
overhead.

The high pressure shifts toward the Eastern Great Lakes tonight
and allows for the cold front and trailing mid-level shortwave
trough to dive southeast into Lake Superior/Upper MS Valley by
daybreak. After a mostly clear to partly cloudy evening, expect
clouds to begin increasing over north-central WI with the leading
edge of showers/isolated thunderstorms pushing into northwest WI
after midnight. Temperatures will not be as cool as last night,
especially over north-central WI with clouds arriving. Look for
readings to be in the lower to middle 50s north, mid to upper 50s
south.

The cold front/mid-level trough are forecast to swing into the
Western Great Lakes region on Thursday and likely will bring
showers/thunderstorms to NE WI. Models are showing a decent amount
of lift along the cold front with modest instability values (capes
from 1000-1500 J/KG, mid-level lapse rates around 6.5 C/KM and
LI`s as low as -5). Enough moisture should have returned with dew
points in the upper 50s to lower 60s and PW values around 1.33
inches, such that a brief downpour is possible with any of the
storms. As for the threat of severe storms, there are two problems
that would appear to limit this threat. First, clouds will be
thickening quickly over the forecast area, thus the amount of
instability could be compromised. The second issue is that the
stronger shear trails the cold front. Cannot completely rule out a
rogue severe storm with freezing levels rather low, thus
borderline one inch hail is possible. The most likely scenario
would be a broken line of convection with small hail and brief
heavy rainfall with the front, followed by more of a steady
rain/isolated thunder as the trailing shortwave trough with its
frontogenetical forcing arrives. Max temperatures to range from
around 70 degrees north-central WI, to the upper 70s east-central
WI (away from Lake MI).

.LONG TERM...Thursday Night Through Wednesday
Issued at 240 PM CDT Wed Jun 29 2016

The sharp upper trough should exit the region Thursday evening
and whatever showers or thunderstorms are left will exit as well.
Then northwest upper flow should provide dry and pleasant weather
through Sunday with cool nights and warm days.

The upper flow becomes zonal after that with shortwave energy
passing by to our north and south. Think we should stay dry for
the Fourth of July and perhaps Tuesday as well, though the models
hint of some convection arriving in the north Tuesday or Tuesday
night.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1233 PM CDT Wed Jun 29 2016

Expect to see scattered cu field (5-6K ft) and ci shield move
across NE WI this afternoon. Light wind regime will also allow the
lake breeze to move inland with winds backing to S-SE as far west
as ATW late this afternoon. VFR conditions are expected through
tonight as high pressure shifts off to the east and a cold front
approaches from the northwest. This cold front and trailing
shortwave trough will sweep across the region on Thursday,
bringing showers and thunderstorms to most locations. MVFR
cigs/vsbys are possible in the vicinity of any of the storms.
Winds will veer to the N-NW behind the frontal passage and could
briefly gust.
&&

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

$$

SHORT TERM.....Kallas
LONG TERM......RDM
AVIATION.......Kallas



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