623 
fxus63 kmpx 080336 
afdmpx 


Area forecast discussion 
National Weather Service Twin Cities/Chanhassen Minnesota 
1036 PM CDT sun Sep 7 2008 


Discussion... 
shortwave energy associated with the broad upper trough stretched 
across the northern Continental U.S....has assisted in the generation of 
widely scattered convection across parts of central and southern 
Minnesota and west central WI this afternoon...where middle level temperatures are 
around -22c. The greatest thunder potential is expected from 
east/south central Minnesota into west central WI...generally east of 
Interstate 35...where mu/surface convective available potential energy have increased to between 
500 and 1000 j/kg along/ahead of the surface boundary. With the 
cold middle level temperatures...cannot rule out small hail across the 
eastern half of the County Warning Area...where effective bulk shear values are 
around 30 knots. The activity should wane after sunset...when 
attention will shift to a stronger shortwave approaching from the 
west. This feature...evident over southern Montana on 19z water vapor 
imagery...will dive across the northern/Central Plains tonight. 
The 12z NAM prognosticated impressive 600-700mb frontogenesis to occur 
across southern Minnesota on Monday morning...as upper divergence in the 
entrance region of the upper jet also develops. The 12z GFS also 
featured these elements...but with a slightly further south 
placement centered more over northern Iowa. Regardless...expect rain 
showers to develop in areas along the Iowa border on Monday 
morning...where sref probabilities of a hundredth are between 60 
and 80 percent. On Monday afternoon...the remainder of the County Warning Area 
will have the opportunity to experience widely scattered 
showers...due to more diurnally driven cold pool action. 


Low level ridging will build in on Tuesday...and bring dry 
conditions. Widespread low temperatures Tuesday morning will 
likely dip into the middle to upper 30s. Temperatures will 
moderate on Tuesday...but remain below normal...with highs in the 60s 
anticipated. 


Southerly flow and slightly warming temperatures arrive for 
Wednesday...as surface cyclognesis ensues over the 
northern/Central Plains. Although some rain showers may arrive 
during the day on Wednesday...the 00z Thursday to 00z Friday 
timeframe continues to appear to be the main window with the highest 
potential for precipitation. Have included 50-60 probability of precipitation for 
Wednesday evening through Thursday morning. 


Confidence decreases dramatically next weekend...as model 
solutions attempt to forecast the fate of Hurricane Ike. 
However...have introduced low chance probability of precipitation for Saturday...as both 
GFS and European model (ecmwf) models forecast a shortwave trough /in some form or 
fashion/ moving across the area. 


&& 


Aviation.../06z taf issuance/ 
weak upper ridge had build over the area this evening. Clouds had 
scoured out over the northern two thirds of the Minnesota and northern 
Wisconsin. Mainly clear skies overnight with some patchy fog 
developing in fog prone areas and river/small streams bogs. 
Meanwhile...a shortwave trough over the northern plains...will move 
east over the upper Midwest by daybreak Monday and move across the 
upper Midwest. Most of the dynamics associated with this shortwave 
trough...will stay well south of main taf sites. Clouds are expected 
to thicken over the taf sites during the day on Monday. Ceilings and 
cloud heights will lower to 4-5k feet above ground level. Surface winds will be 
northwest at 5 to 10 miles per hour then becoming light and variable or under 6 
knots by sunset Monday. 


&& 


Mpx watches/warnings/advisories... 
Minnesota...none. 
WI...none. 
&& 


$$ 


Ls/jvm