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afdind 


Area forecast discussion 
National Weather Service Indianapolis in 
616 am EST sun Nov 23 2008 


Aviation...discussion for 12z tafs. 
VFR through 24/06z. A cold front will pass through central Indiana 
late tonight. Ahead of this front southerly winds will bring some 
moisture back to the state. 


MVFR clouds will roll in around the same time rain begins after 06z 
tonight. At this time it looks like only ceilings will be MVFR and will 
keep visible at p6sm. Rain will continue through the end of the taf 
period. 


&& 


Previous discussion...high pressure was found across Ohio and wva early this 
morning with light southeast winds. Surface dew points were still very 
dry...mainly in the teens. Sat pictures show clear skies across Indiana 
this morning. 


Main forecast challenge will be probability of precipitation. 


Models remain in pretty good agreement and will use a blend. 


Time height sections show a dry column today with subsidence...which 
should be expected underneath the weak upper ridge. 800 mb shows some warm air advection 
today with 800 mb temperatures near 0.5c. However with very cool start...surface 
temperatures in the lower 20s...highs will still struggle to reach the middle 
and upper 40s. Still it should feel much warmer than the past couple 
of days. 


295k isentropic surface shows a tongue of moisture with some vertical velocity poised 
to push across Indiana ahead of the cold front and approaching upper 
trough. Best dynamics appear to arrive late overnight...thus will keep 
the early part of Sunday evening dry...but have likely or higher 
probability of precipitation overnight. Models have warmed up slightly from last night/S run 
and as stated in the previous discussion...precipitation type now appears to 
be mainly rain as forecast soundings across the area show much of the 
lower levels above freezing. With precipitation expected will lean toward 
expected wetbulb temperatures for lows. 


Cold air advection returns on Monday and Monday night as the quick moving cold 
front pushes east and cold northwest flow resumes. Again a few lingering 
flurries appear possible on Monday...but most of the moisture 
appears to be pre-frontal. Broad cyclonic flow and cold air advection should also 
bring about a return to the doldrums of gloomy...cold SC clouds and 
along with the renegade flurry on Monday night and Tuesday. Given 
this will stick close to mavmos on Monday night lows...but cooler than 
mavmos on Monday and Tuesday highs. 


Little change in the short term extended as high pressure resides across 
the area through at least Thanksgiving. GFS hints at a system pushing 
through the Tennessee Valley next weekend...but will wait another run 
for now before making any changes. 


&& 




Ind watches/warnings/advisories...none. 


$$ 


Aviation...Sally 
public...puma