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Area forecast discussion 
National Weather Service Green Bay WI
215 PM CDT Friday Aug 22 2014

Forecast discussion for routine afternoon forecast issuance

Short term...tonight and Saturday
issued at 215 PM CDT Friday Aug 22 2014

The latest rap analysis and satellite/radar imagery show a weak
area of low pressure spinning over western Wisconsin early this
afternoon. Although upper divergence in the right rear quadrant of a
jet streak has shifted off to the east...convergence north of a
surface warm front has generated scattered showers and an isolated
thunderstorm over north-central Wisconsin. Also observing rather
bubbly looking cumulus along a cold frontal type feature moving into
central Wisconsin though convergence looks quite weak...and the
only returns are located over northeast Iowa. The atmosphere is
growing unstable ahead of this trough/cool front with ml convective available potential energy
growing to greater than 1000 j/kg...and cin falling rapidly. The
NAM creates convection over central Wisconsin later this
afternoon...so this is something to keep an eye on. Included a
isolated thunderstorm mention for the rest of the afternoon over
central Wisconsin. Meanwhile...a large upper trough over the Pacific
northwest will shift east causing a warm front to re-organize over the
plains on Saturday. Precipitation chances and fog potential remain the
main forecast concerns.

Tonight...models are having a tough time latching on to that low
level circulation over western Wisconsin. The NAM and to a lesser
extend the Gem appear to have a better handle on this feature than
other guidance. But confidence will remain low in any case. Both
the NAM and Gem show this surface low weakening later this afternoon
or this evening and morphing into a surface trough over central and
north-central Wisconsin. This will keep an isolated to scattered
threat of showers and storms into the evening...and possibly into
the overnight hours too. This trough will also promote fog development
in these areas tonight and think another dense fog advisory will be
possible for the early morning commute tomorrow. Light easterly
winds may also advect areas of marine fog inland into the Lakeshore
counties tonight. Warm and muggy with lows in the 60s.

Saturday...low pressure will emerge into the Central Plains ahead of
a deep Pacific northwest trough. The low level flow will reorganize and a warm
front will lift into southwest Wisconsin in the afternoon. This
looks to be a little slower than yesterdays runs and will back off
precipitation chances during the morning. Chances improve during the
afternoon over central and north-central Wisconsin but am skeptical
since the front will still be well southwest of the region and
middle-level ridging sharpens aloft. So will match with other offices but
bring up concern to the next shift. Once the morning fog and low
clouds burn off...continued warm and humid with highs in the upper
70s to lower 80s.

Long term...Saturday night through Friday
issued at 215 PM CDT Friday Aug 22 2014

Saturday night into Sunday...the upper ridge gets nudged to the
east a tad while a broad upper trough approaches from the
northern and Central Plains. A deepening low pressure system will
lift northward over the northern plains...and lift a warm front
north over the area. Some forecasts generate some convection with this
front Sat night into Sunday morning. Convection may struggle to
develop due to proximity to the upper ridge so kept probability of precipitation on the low
side and decreased the duration of the convection mention.
Isolated convection may linger Sunday morning across northern
Wisconsin...but by noon the h850 boundary is prognosticated to be well
north of the area. Any precipitation chances during this period
will tend to be focused toward northwest Wisconsin toward the best
height falls.

Sunday night into Monday...next chance of convection along a
trough or weakening cold front. Most model runs diminish the precipitation
as it works into eastern Wisconsin closer to the upper ridge which
remains over the eastern Great Lakes and much of the east third of
the country. The brunt of the convection will likely track over
northwest Wisconsin and especially over Minnesota near the
surface and 850 low lifting northeast.

Monday night...broad rrq region of the upper jet focuses the
convection over the Central Plains while while weak high pressure
builds into the region in the wake of the frontal passage. The GFS was the
odd model out with stalling the front over the area and
continuing convection Monday night.

Most of the models for the rest of next week...the upper pattern
shifts from a southwest flow aloft to a nearly zonal flow late in
the week...but some agreement with most models with respect to a
more robust short wave with rrq upper jet region passing through
toward middle week. Could see another round of a soaking rain with
the surface front and h850 front interacting with the upper jet.

Temperatures will be above normal through Tuesday...and well above
normal in a sticky air mass Sunday especially if the clouds clear
out. Temperatures cooling back to near normal later next week.
&&

Aviation...for 18z taf issuance
issued at 1206 PM CDT Friday Aug 22 2014

A warm and very moist late Summer airmass will remain in place
through the taf period. Weak low level convergence will promote
isolated to scattered shower development this afternoon over
north-central and possibly far northeast Wisconsin. The isolated
showers could linger into the evening over far north-c Wisconsin.
Otherwise...expect ceilings and visibilities to lower quickly by middle to late
evening across the region...with areas of dense fog developing again
late tonight. Ceilings and visibilities to improve very slowly tomorrow
morning.
&&

Grb watches/warnings/advisories...
none.
&&

$$

Short term.....Mpc
long term......tdh
aviation.......mpc

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