051 
fxus63 kind 070418 
afdind 


Area forecast discussion 
National Weather Service Indianapolis in 
1220 am EDT Tuesday Oct 7 2008 


Aviation...discussion for 06z tafs 
VFR expected through the majority of the taf period. 


Low level moisture is slowly returning to central Indiana ahead of a 
low pressure system and cold front that will reach central Indiana 
on Tuesday evening. Strong warming ahead of the cold front...which 
isnt expected to pass through the state until Wednesday...will allow 
for some instability and possible thunderstorms. At this time 
thunder isnt expected to be widespread enough to include in the 
taf...especially this far out so will continue with cumulonimbus until better 
timing can be achieved. 


As moisture continues to increase...especially after 18z 
Tuesday...clouds will thicken and eventually become MVFR but that 
may not happen until after the end of this taf valid time. 


By 00z-03z rain will likely have spread into all taf sites and will 
add this to the 06z issuance. 


&& 


Previous discussion... 


Forecast focus is on chances for rain Tue-Thu. 


At 18z an upper trough was across the Southern Plains with an upper ridge 
across the forecast area /fa/. High clouds were across the forecast area with 
temperatures in the 70s. 


Models are in better agreement...although differences remain in 
strength and location of upper low for middle week. GFS still looks too 
strong with upper low compared to other models. However per National 
model discussion NAM had some initialization issues...so do not 
completely trust the NAM either. Thus believe reality will be 
somewhere in between and thus took a blend of their solutions. 


Expect some middle and high clouds around tonight...thickening some 
toward morning as upepr system begins its move to the east. Thus partly cloudy 
or becoming partly cloudy looks good for skies tonight. Higher dewpoints 
are moving into the area as well. A blend of met/mav temperatures reflects 
these conditions and looks good. 


Clouds will continue to increase on Tuesday but still expect some sun 
and warm advection to boost temperatures to near the similar mav/met 
numbers. NAM/GFS bring precipitation well into the forecast area by 00z but NAM precipitation 
has a bulls-eye that looks out of place. Short range ensembles 
/srefs/ are slower than the NAM/GFS. Given this and the fact that 
the atms will need a little time to moisten up will not go quite as 
high as mav probability of precipitation. However given trend of speeding up this system and 
the fact that the 850 jet looks to impact the area by 00z will 
expand smaller chance probability of precipitation farther east. 


As the system moves east across the forecast area Tuesday night precipitable water 
values are well over an inch. Good isentropic lift will occur and 
q-vector convergence plots indicate additional forcing as well. Thus 
feel that the categorical probability of precipitation continue to be warranted. Instability 
not impressive so will go with just scattered thunderstorms with the occasional rain. 


System will be slow to exit the area and enough forcing will be 
around to probably get some measurable precipitation on Wednesday...especially 
early. So will continue likely probability of precipitation on Wednesday. 


Trend has been to speed up the exit of the system so have removed 
probability of precipitation for Thursday. High uncertainty exists on the evolution of the 
pattern for the weekend and early next week. Will keep things dry 
for now. 


&& 


Ind watches/warnings/advisories...none. 


&& 


$$ 


Aviation...Sally 
public...cs