192 
fxus63 kmpx 070408 
afdmpx 


Area forecast discussion 
National Weather Service Twin Cities/Chanhassen Minnesota 
1108 PM CDT Sat Sep 6 2008 


Discussion... 


Initial few days of forecast still dealing with several fast moving 
short waves embedded in medium wave trough digging slightly into the 
central Continental U.S.. went with a blend of the gfs40 and European 
model...due to its handling of developing convection across 
Dakotas and west central Minnesota...and its depiction of location 
of Hannah per vapor loop. Weak surface trough from north central Minnesota 
to south central sodak...will slowly trek east and extend from northwest WI 
to south central Minnesota by sun 18z. 300k surface isentropic anal still the 
Champ for placement of precipitation trends right through end of 
period. Had a short lived strong thunderstorm across far western laq 
qui parle County earlier this afternoon. However...lapse rates and 
lifted indice's indicating at best isolated boomers for the remainder of the 
evening hours and into Sunday. Best conditional pressure deficits 
clearly seen over southern Minnesota this evening and quickly exits stage 
right into southeast Minnesota by 12z. Another 500 mb trough dives into far 
western County Warning Area by dawn on Sunday. Although very little jet support 
evident initially...nose of 115kt jet axis seen this region by 
07/18z. Trough will weaken as it proceeds east...but enough 
instability available for chance probability of precipitation and light precipitation into 
the late afternoon. 


Big change in forecast arrives Sunday evening into Monday as 
strongest 500 mb wave marches into region as medium range trough digs 
into NE Colorado...and warm frontal boundary draped across central Minnesota. 
This system will produce best shot of convection across southern 
half of County Warning Area...with quantitative precipitation forecast values indicating possibly healthy .40 to .75 
inches of moisture by end of day Monday. Divergence aloft extremely 
healthy late Sunday evening into Monday morning per coupled jet 
structure formation from Great Lakes back into the eastern Dakotas. 
Rain chances will subside to zero by end of Monday evening...as 
surface cyclone over western Kansas deepens appreciably as it treks into 
Great Lakes region by this time frame. 


Middle week concerns for frost (tuesday morning) has been negated due to 
stronger gradient and additional nighttime cloud cover instigated 
by zonal flow. Next chance for precipitation arrives on Wednesday during the day 
as next surface wave develops over central NE. Both GFS and European 
continue to indicate a slightly weaker system during the past several 
runs. Most quantitative precipitation forecast now expected over Iowa...and far southeast Minnesota very early Thursday 
morning. Temperatures should remain at or slightly below seasonal 
trends prior to Thursday...and slightly above thereafter. 


&& 


Aviation.../06z taf issuance/ 


One short wave departing western WI while another one nearing western Minnesota. 
First one will take with it the clouds over eastern Minnesota and western WI 
gradually. Where it rained...clearing will likely promote some fog 
development as has already been seen in places of SW and west ctrl 
Minnesota. Clouds from next wave will begin to spread in over western taf 
sites soon overnight with showers knocking on the door to axn soon 
after start to taf. Showers should decrease in coverage somewhat 
into the morning hours as the favorable area for development 
approaches eastern and southern Minnesota. Still worthy of vcsh though. A little 
more coverage expected during the afternoon in western WI. Isolated cumulonimbus and 
thunder possible...as has been seen in South Dakota. However...not enough 
confidence to mention in taf at this time. Overall...VFR 
conditions should prevail through this taf period with only minor 
windows for MVFR ceilings or visbys in rain. 


&& 


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


$$ 


Ajz/mtf