713 
fxus63 kind 030609 
afdind 


Area forecast discussion 
National Weather Service Indianapolis in 
108 am EST Wednesday Dec 3 2008 


Discussion... 
main challenge to this forecast will be timing/covering and precipitation type this 
afternoon and tonight as a cold fnt currently from the u.P. To north central Kansas 
moves across central Indiana. Currently 11-3.9 micron loop and surface observation 
were just showing some patches of cirrus across the forecast area in zonal flow ahead 
of digging and progressive northwest upper trough. 


The NAM has now caught up nicely with the other models regarding 
tngt's cold fnt and subsuent cooling of the column and changeover to 
snow. Previous forecast seemed to have a good handle on timing of the 
changeover...et cetera as it agreed with the quicker and more consistant 
GFS. So...only made minor changes with good chance rn probability of precipitation after 18z 
today and likely probability of precipitation tonight changing over from 00z-06z NW-se. Quicker 
changeover favor highest snow amounts near laf but still only 
slightly more than an inch expected. 


A mix of mainly high clouds and sunset is expected on Thursday with high 
clouds continuing Thursday night as zonal flow is featured along with surface 
high pressure building in from the northwest. Next chance of snow is Thursday night as 
another cold fnt approaches from the west. 


With cumulus expected to increases this afternoon per model time secs and 
upstream surface observation trends across the northern plains...will go on the low side 
this afternoon for highs per the GFS MOS. Tonight...MOS is really close 
and looks good both with consistancy and considering the expected 
cloud cover and low level thermal profile forecasts. 


&& 


Aviation...discussion for 03/06z tafs 


VFR conds expected for just under first half of taf period with few middle 
cloud and scattered-broken high clouds. Winds aloft /near 850mb/ will 
increase to at or above 40kt by 12z. 


A cold front will move into the area late Wednesday afternoon. VFR deck with 
scattered rain showers will develop by 17z or so with rain chances increasing 
during the day from west to east. Surface winds will be gusty with gusts near 
25kt possible. Conds will deteriorate to MVFR visibilities by 20z or so 
with IFR conds possibly developing by 00z. Visibilities should drop to MVFR 
in rain. For now...have brought ceilings down to just above IFR by 00z 
until confidence grows. 


After 04/00z mix of rain and snow will change to a brief period of snow 
before ending as cold air rushes in. 


&& 


Ind watches/warnings/advisories...none. 


&& 


$$ 


Public...mk 
aviation...cs/cp