Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 200328

Area Forecast Discussion
National Weather Service Green Bay WI
1028 PM CDT TUE JUL 19 2016

Updated aviation portion for 06Z TAF issuance

.SHORT TERM...Tonight and Wednesday
Issued at 258 PM CDT Tue Jul 19 2016

The latest Rap analysis and satellite/radar imagery show surface
high pressure centered over the central Great Lakes early this
afternoon.  Partly cloudy to mostly clear skies are prevailing over
northeast and north-central WI close to this surface high.  Farther
west however, a warm front is stretching from North Dakota to
central Illinois.  An mcs has turned southeast over Iowa, while
additional scattered convection has regenerated ahead of a weak
shortwave impulse that is riding over top of the strengthening sub-
tropical ridge over southern Manitoba.  Forecast concerns revolve
around precip chances as the warm front moves into the region on
Wednesday. Overall forecast confidence is low over the next 24 hours.

Tonight...The warm front will gradually lift northeast as mid-level
ridging shifts east into the western Great Lakes.  At the same time,
the shortwave over southern Manitoba will eventual make a turn
southeast across northern Minnesota into western Lake Superior.
Given the track of the ongoing mcs over Iowa, and lack of convection
upstream, think will see a mostly clear and warm evening.  Then
think will see mid-clouds increase as the warm front draws closer to
the region, and mid-level moisture transport increases.  With
elevated capes increasing to around 1000 j/kg late tonight, the
shower and thunderstorm threat will gradually increase during the
overnight hours over central and north-central WI.  Shear values are
relatively low, so mainly thinking brief heavy rainfall as the main

Wednesday...The warm front will continue to lift northeast across
the forecast area as the shortwave moves over Lake Superior.  With
forcing continuing through the morning hours, appears the best
chance of showers and storms will occur then, before they shift
southeast during the afternoon.  Models are relatively inconsistent
though, so confidence in timing/placement of precip is pretty low. 0-
6km bulk shear values remain in the 20-25 kts range, so the marginal
severe storm risk from SPC looks good.  Heavy rainfall looks like
the main threat once again.  Dewpoints will be creeping up towards
the 70 degree mark during the afternoon which will make it feel
rather sticky.  Temps warming a degree or two into the low to mid

.LONG TERM...Wednesday Night Through Tuesday
Issued at 258 PM CDT Tue Jul 19 2016

A large upper ridge centered over the Plains states
will produce very warm and humid weather across Wisconsin Wednesday
night through Friday, though the magnitude of the heat and humidity
is still uncertain due to the proximity to short wave energy moving
through the southern part of the westerlies.

One short wave moves across the region Thursday, which should
help produce showers and thunderstorms north of a surface warm
front. The front will likely be across the northern part of our
forecast area. Heat advisory criteria will likely be reached
across the southern half of the forecast area Thursday afternoon.

A cold front will bring somewhat drier air Friday and may keep
heat indices below advisory criteria in all of our forecast area.
Fast, nearly zonal flow will make forecasting difficult this
weekend and early next week as timing and location of the fronts
are uncertain.

.AVIATION...for 06Z TAF Issuance
Issued at 1009 PM CDT Tue Jul 19 2016

Thunderstorm chances are the main concern late tonight through
Wednesday night. Watching a thunderstorm complex across northern
Minnesota this evening. The wrf model did not depict this cluster
of storms while the latest HRRR model indicated this cluster of
storms. The HRRR model shows this cluster of storms weakening
by 05z. Not sure this will happen as quickly as the HRRR would
suggest due to 40 knots of shear aloft. If storms do hold together
longer than expected, they could sneak into western Wisconsin.
Additional thunderstorms are expected to develop across Minnesota
and Iowa later tonight as low level jet cranks up. Another area of
concern is across north-central and northeast Wisconsin where
latest meso-models indicated isolated precipitation breaking out
between 08z and 13z. Can not totally rule out an isolated storm
in this region, but will not put into the 06z tafs. The warm front
will lift northward on Wednesday, bringing a continued chance of
thunderstorms into Wednesday night. Timing of storms at each
individual taf site difficult at the moment due to the isolated/
scattered nature of the storms. Will pick the best times for
storms at each taf site and later shifts may need to adjust or
extending timing of storms as they move across the region.




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