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Area forecast discussion 
National Weather Service Green Bay WI
649 PM CDT Sat Sep 20 2014

Updated aviation portion for 00z taf issuance

Short term...tonight and Sunday
issued at 308 PM CDT Sat Sep 20 2014

Tonight and Sunday

Rather complex evolution will evolve over the forecast area
overnight as very strong upper jet and shortwave plunge southeast
into the western Great Lakes.

Weak cold front/surface trough currently drifting southeast across
the eastern part of the forecast area. A weak shortwave impulse is
also traversing eastern Iowa/northern Illinois and is helping to
generate area of showers and thunderstorms over southeast
Wisconsin to northern Illinois along and ahead of the front. A few
showers have also developed as far north as Manitowoc County near
the front but these should quickly move off to the east within the
next hour or so. Meanwhile further north...another more
substantial short wave disturbance continues to move eastward north
of Lake Superior. This impulse has also helped to generate another
area of thunderstorms over extreme eastern Upper Michigan. In the
wake of this disturbance visible satellite imagery and surface
observations suggest some enhanced cumulus/SC along the Wisconsin
Michigan border with boundary layer winds shifting more northerly
to the north of this feature. Winds have been quite gusty across
northern Wisconsin reaching 30 miles per hour at imt at times.

The primary weather feature this evening and overnight will be a
very strong upper-level jet maximum and associated shortwave that is
forecast to dive southeast into Wisconsin. As this feature
continues to approach the area...organized and rather strong
mesoscale lift will develop helping to generate shower and
thunderstorm activity. Short term model guidance suggest that a northwest-
southeast orientated surface trough will develop over northcentral to
northeast Wisconsin this evening in response to pressure falls
near the lfq of the approaching upper-level jet maximum. Latest radar
data indicates well-organized quasilinear convective complex that
has already developed near the lfq of the jet and has already
produced some severe weather over the eastern Dakotas and western
Minnesota. Model guidance races this feature eastward this
evening. Based on current observations...this quasilinear mesoscale convective system
appears to be propagating faster than model guidance is suggesting.
The leading edge of this convective complex may make it to the
western portion of the forecast area by 01 or 02z. In
addition...the majority of model guidance also suggest some shower
activity may also develop within increasing area of blyr
convergence further east along the afformentioned northwest-southeast orientated
surface trough that will be developing across northeast to
northcentral Wisconsin early this evening. As we approach the late
evening...the quasilinear mesoscale convective system and scattered upstream shower
activity will congeal. Thus expect fairly well-organized band of
showers and embedded thunderstorms to push southeast across the
forecast area around and after midnight. Given the strength of the
upper dynamics and fairly steep middle-level lapse rates...there is
certainly some potential for some of the storms to produce
marginally severe hail and perhaps some strong wind gusts. Feel
best chance of this occurring will be over central portions of the
forecast area later this evening with model guidance weakening the
convection after 09z as it approaches the eastern part of the
forecast area.

Although strong dynamics should be east of the forecast area
shortly after 12-14z Sunday...lingered low probability of precipitation well into Sunday
afternoon as upper trough axis will still be over the area with
associated surface trough moving southward across the area during
the early afternoon to help focus scattered shower activity. By
late afternoon..drier air should begin to work its way southward
across the forecast area allowing skies to clear somewhat. Temperatures
will be markedly cooler than today with daytime highs mainly in
the lower 60s.

Long term...Sunday night through Saturday
issued at 308 PM CDT Sat Sep 20 2014

Extended models are in general agreement in the large-scale with the
mean flow transitioning from a rockies upper ridge/E-cntrl Continental U.S. Upper
trough early next week...to a western Continental U.S. Upper trough/eastern Continental U.S. Upper ridge
late next week. The forecast issues have to deal with smaller scale
features...especially a weak shortwave trough middle-week headed toward
the western Great Lakes. This pattern change would send NE WI from
below normal temperatures/above normal precipitation...to a warmer/drier pattern.

The center of an area of hi pressure is forecast to move southeast from the northern
plains toward the middle-MS valley Sunday night. This places NE WI
under the northern fringes of this surface hi...with mainly clear skies and
a light north-northwest wind. Depending on how much precipitation falls tonight/Sunday
morning...there could be some patchy fog developing over much of
the forecast area. Another concern would br frost potential over the
north late Sunday night. Boundary layer winds to be in the 10 to 15
knots range and may not be strong enough to prevent temperatures from reaching
the middle 30s over northern WI. Have included patchy frost wording
generally north of a Merrill-Antigo-Wausaukee line.

The surface hi drifts east into southern sections of the Great Lakes/Ohio
River valley on Monday with mostly sunny skies...west winds under 10
miles per hour and seasonal temperatures for late September. Look for maximum temperatures to
range from the lower 60s Lakeside (due to a lake breeze) to the middle
to upper 60s elsewhere.

As the surface hi heads farther to the east Monday night...modest warm air advection
begins to develop over WI...especially after midngt. 800 mb temperatures are
about 4c degrees warmer compared to Sunday night...thus do not expect
surface temperatures to quite as cool. The west-SW winds aloft will also begin to
bring a touch of moisture back into WI...therefore cannot rule out
another bout of patchy late night fog over the forecast area. Min temperatures
to range from the lower to middle 40s north...middle 40s to around 50 degrees
south. Return flow in full effect by Tuesday as winds back to the
south (except S-southeast near Lake Michigan as the lake breeze moves inland)
and warmer/more moist air pushes into WI. The forecast area to reside
on the western edge of the departed surface hi...thus expect to see
another mostly sunny day with maximum temperatures in the middle to upper 60s
Lakeside...upper 60s/lower 70s elsewhere.

Headed into mid-week...the main focus to be on the movement of a
shortwave trough (remains of a California closed upper low) across the central
Continental U.S.. Tuesday night appears to remain quiet under mostly clear skies
and light S-southeast winds. This shortwave trough lifts NE into the upper MS
valley/Midwest on Wednesday in a weakening state between upper rdgs over
The Rockies and eastern Continental U.S.. clouds will gradually increase over central
WI with the leading edge of light showers impinging on north-central WI
late in the day. Eastern WI should see another day with mostly sunny
skies as temperatures to reach into the lower 70s...slightly cooler north-central
and Lakeshore.

An interesting phenomena then takes place Wednesday night into Thursday as the
eastern Continental U.S. Upper ridge retrogrades westward and starts to pinch off the
shortwave trough still situated over the upper MS valley/Midwest. Northern
sections of the shortwave trough weakens and eventually dissipates...
while southern sections of the trough drifts SW and tries to become a weak
closed upper low over the Central Plains. If this scenario is correct...
central WI may have a small shower chance Wednesday night into Thursday morning...but
eastern WI may end up not seeing a drop of rain.

The end of the week will feature a deep upper trough hitting the West
Coast and a large upper ridge over the eastern half of the Continental U.S.. this
set-up would provide for dry conditions with above normal temperatures.
In fact...cannot rule out maximum temperatures on Sat reaching 80 degrees over
parts of central WI.
&&

Aviation...for 00z taf issuance
issued at 641 PM CDT Sat Sep 20 2014

A strong upper-level disturbance will quickly approach the
forecast area this evening and generate a band of showers and
thunderstorms. This band is expected to reach rhi/auw/cwa around
03z...and atw/grb/mtw around 05z-06z. After the initial band moves
through...an area of steady light to moderate rain is expected to
consolidate over the forecast area late tonight into Sunday
morning. MVFR/IFR conditions will likely develop with the steady
rain. Conditions will gradually improve as the rain tapers off
Sunday morning...with VFR conditions returning by midday or early
afternoon.
&&

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

$$

Short term.....Esb
long term......kallas
aviation.......kieckbusch

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