Weather

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fxus63 kgrb 070916 
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Area forecast discussion 
National Weather Service Green Bay WI 
416 am CDT sun Sep 7 2008 


Short term...today through Monday. 


Forecast challenge will be precipitation chances later today into this 
evening then again later Monday...as series of shortwaves forecast to 
move across the upper Midwest/western Great Lakes. 


Water vapor imagery shows several weak shortwave disturbances 
enbedded in broad longwave trough situated across the central 
Continental U.S.. couple weak disturbances over central Iowa and western WI 
managed to generate a few scattered light showers early this 
morning but appear to be of little consequence. 


Focus turns upstream where more potent shortwave moving across 
the Dakotas will move into the forecast area later today. NAM/GFS 
generally similar on handling of this feature and bring associated 
weak surface front/trough across the forecast area later this afternoon/early 
evening. Appears to be enough forcing and instablity to generate 
scattered showers and perhaps a few thunderstorms this afternoon 
into early evening. Focused highest probability of precipitation across the central and 
north today. At this time...precipitation looks to be scattered in nature 
with generally light rainfall amounts expected. System should exit 
the area before midnight and tapered probability of precipitation and quantitative precipitation forecast accordingly. 


Stronger system then takes aim for the upper Midwest late Monday and 
Monday night. More differences in model solutions with the GFS 
faster...bit further north and showing a stronger surface 
reflection compared to NAM. UKMET/European model (ecmwf) more similar to NAM and 
thus have leaned more toward these solutions. Made a few minor 
adjustments to timing of precipitation into forecast area on Monday and 
focused more on afternoon hours. Was not quite as optimistic as 
HPC on quantitative precipitation forecast amounts and adjusted quantitative precipitation forecast further south and lowered 
amounts some...showing a bit more of a north-south gradient 
across the forecast area. Temperatures a bit tricky on Monday depending 
on timing of precipitation. Leaned more toward cooler mav guidance. 


Long term...Monday night through Thursday. 


Zonal pattern continues this period with main forecast concerns 
focused on precipitation chances Monday night with passage of yet another 
short wave trough. Models continue to show inverted trough/wave feature 
at surface shifting northeast through the western lakes. Strong 
850 baroclinic zone expected to lie along Illinois/WI border with sig 
warm air advection pattern into southern WI. NCEP models consistent last two nights 
indicating strong frontogenetic signature to the north over east 
central and central WI. GFS strongest with features...have trended 
towards weaker/slightly further south ensemble forecasts of 
sref/GFS. System shifts east of area by Tuesday morning...with high 
pressure moving in. With 850 temperatures dropping to around 3 degrees 
Tuesday morning..look for temperatures to run well below norms into Wednesday. In 
future periods...slowed down arrival of precipitation from next system to 
Wednesday night. 
&& 


Aviation... 
generally MVFR ceilings and visibilities with scattered showers 
and perhaps a few isolated thunderstorms...especially after 18z 
today. Airport most likely to be impacted by scattered activity 
this afternoon into early evening will be rhi. 
&& 


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


$$ 
Esb/te