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Area forecast discussion 
National Weather Service Green Bay WI
1158 am CDT sun Apr 19 2015

Updated aviation portion for 18z taf issuance

Short Monday
issued at 327 am CDT sun Apr 19 2015

The latest rap analysis and satellite/radar imagery show split flow
over central North America early this morning. In the southern
stream...upper level low pressure is spinning over western
Kansas/eastern Colorado. Ahead of this feature...showers and
thunderstorms are occurring from Nebraska to Louisiana. Even
further northeast...mid-level moisture transport and ill-defined
shortwaves are also creating showers and a few thunderstorms from
western Wisconsin into Illinois. A couple spotty showers popped up
shortly after midnight over Wood County to The Dells...and will have
to carry an isolated mention early this morning across the
I-39/Route 51 corridor. In the northern stream...shortwave energy
is progressing east over the northwest plains. As these features
move east...precipitation chances and timing are the main forecast concerns.

Today...low pressure over the northern plains will head east while
the southern stream low will lift northeast over the central
Mississippi Valley. Weak shortwave activity rotating on the eastern
periphery of the upper low over western Kansas will lift north
across the western Great Lakes today but into a more stable and
drier airmass. Despite this...the higher res models and RUC depict
spotty showers developing over central and northeast Wisconsin this
morning which bear some weight given the spotty showers popping up
over The Dells at this hour. As a result...quite difficult to add
much temporal resolution to the forecast this morning other than
saying slight chance of a shower. Forcing increases over western
Wisconsin during the afternoon when a fgen band moves across that
part of the state. The eastern edge of the induced rain band will
likely be pushing into north-c Wisconsin late in the afternoon. Am
thinking eastern Wisconsin will remain mostly dry due to NE flow. The
slower arrival of the precipitation will help temperatures rise into the
middle 60s over central WI. Cloud cover and east winds will support
much cooler readings over eastern WI though.

Tonight...the medium range models track the southern stream surface
low from central Illinois/Indiana to northern lower Michigan. Some
possibility that the low will track west of this line in the
mesomodels though. Comma head precipitation from this low looks to move
into northeast Wisconsin by middle to late evening. Meanwhile...rain
band associated with middle-level fgen ahead of the northern stream
wave will shift east through the night across central and eastern
Wisconsin. Seems like a good recipe for periods of rain across the
region. Lows ranging from the upper 30s north to middle 40s south.

Monday...the fgen rain band will gradually be weakening as it moves
east across eastern Wisconsin during the morning and exits during
the afternoon. The middle-level dry slot will work overhead in the
wake of the rain during the afternoon and may see a few peaks of
sunshine. Otherwise...becoming breezy with highs in the middle 40s
north to low 50s south.

Long term...Monday night through Saturday
issued at 327 am CDT sun Apr 19 2015

Closed upper low will bring unsettled and cool conditions to the
region Tuesday into Wednesday. The upper low will gradually pull
away Thursday and Friday...but cyclonic flow could still bring a
small chance of precipitation Thursday into Friday across the
far north. Despite the calender stating its late April...some snow
is in the forecast late at night into the morning hours. Could be some
minor accumulation across the far north Tuesday morning and again
Wednesday morning.

Below normal temperatures will continue into next weekend with dry
conditions expected on Friday. Only minor changes made to precipitation
chances and temperatures during the period.

Aviation...for 18z taf issuance
issued at 1146 am CDT sun Apr 19 2015

Broken midlevel ceilings continue this afternoon into the
evening...though VFR conditions should prevail. Low pressure then
move across the Great Lakes region tonight and will result in
an area of steady rain overnight. Precipitation should be slower to
arrive than previously forecasted...with rain arriving late early
tonight through midnight. Low end IFR conditions are expected with
this area of rain...with LIFR ceilings possible as current observation in
area of incoming precipitation in Illinois/in show scattered ceilings below 500ft.
LIFR conditions in current rain not widespread enough and guidance
waffling on how low ceilings will not enough confidence to add
it to the tafs at this time...but will be something to monitor.
Heaviest rain and worst conditions will likely be over eastern taf

Rain will taper off Monday morning in north-central Wisconsin
with MVFR ceilings possible by the second half of the morning. Light
rain will continue further east with IFR conditions most likely
holding tight until later in the morning. Winds will back from
southeast this north northeast
Monday as a cold front sweeps through the state.


Grb watches/warnings/advisories...


Short term.....Mpc
long term......eckberg

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