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fxus63 kiwx 210820 
afdiwx 


Area forecast discussion 
National Weather Service northern Indiana 
420 am EDT sun Mar 21 2010 


Aviation... 
VFR conds expected through the period as shallow Post frontal cold pocket 
erodes/mixes out in response to weak warm air advection aloft ahead of deep Southern 
Plains cyclone. East/NE surface winds 10-15kts will continue. 


&& 


Short term... 
deep Southern Plains cyclone cutoff over NE Texas will slide eastward through northern 
la and emerge into western MS by this evening and well S of any prior 
available guidance which adamantly took this system on a much more northern 
track. Thus given deepening ll negative Theta-E wedge across County Warning Area and demise 
of upstream precipitation band across Illinois see little reason to hold west/any pop 
mention for today outside token slight chance mention extreme S this afternoon 
and perhaps far northwest this morning pending echo evolution toward issuance 
time. Failure of any appreciable top-down saturation outside northwest edge 
of County Warning Area suggests subsident mixing in wake of polar jet streak shld 
allow for some partial insolation through morning in broken middle cloud 
deck and will bump temperatures further especially in light of poor performance southeast 
half yesterday. 


Poor model handling woes continue overnight west/00z guidance even further 
right of Center West/track of closed cyclone west/a consensus position near 
kbhm Mon/12z. Northern extent of prognosticated quantitative precipitation forecast looks very suspect per 00z 
radiosonde observations boundary layer moisture profiles out of Kiln/kohx and further 
discounted west/lack of appreciable ascent even across far southeast County Warning Area lt 
tonight as ll follow backs further. Continued erosion in guidance probability of precipitation all the 
more reason to chop existing grids further overnight and drop likely 
mention save extreme southeast. Temperatures problematic as well far northwest where clearing 
is likely as kbeh holds great bust potential if decoupling occurs 
and will adjust northern area lower. 


Deep occluding circ finally looks to turn northeastward Monday and open while 
accelerating some as well. However western extent of btr ll moisture rtn 
wrapping through northern portion of cyclone still remains quite 
uncertain. Have retained continuity west/prior western extent of low chance 
pop mention but raised southeastern area significantly on the premise that 
strongly clustered 00z model guidance has finally resolved 
intensity/track trends and will extend trough Monday night (esp 
evening) southeast County Warning Area given likely backlash rain showers west/slower northeastward ejection 
and hope that bears measurable. Temperatures remain difficult especially in 
context of diabatic cooling southeast and likely isolation northwest Monday and sided 
west/sref which matched up close to met/mav MOS blend. 


&& 


Long term.../Tuesday through Saturday/... 


Upper ridging will be working into the region in the wake of 
departing system on Tuesday ahead of trough over the intermountain 
west which will follow...weakening as it does...south of a cold 
vortex over central Canada which will slide southeast late week 
along with accompanying surface ridge. This results in temperature recovery 
Tuesday and Wednesday with highs into the 50s...though guidance is cooling on 
Wednesday as weak frontal passage allows somewhat cooler air to 
infiltrate. Midweek remains dry as GFS has continued to back off 
already weak moisture convergence along this boundary. Stayed above 
mex guidance Wednesday but cooled temperatures slightly as 00z European model (ecmwf) supports 
slightly cooling 850 mb temperatures across the north as ridge flattens. 


By late week...weakening trough moves east and phases with trough 
dropping southeast from Canada. A situation eerily similar to the 
current system with the exception of weakening intensity. Surface ridge is 
currently shown in both op models to progress far enough south to 
put northern fringe of precipitation associated with developing boundary just 
south of the County Warning Area. 12z/00z European model (ecmwf) a bit faster with moisture return and 
given recent trends slower is better and will keep chance pop mention 
timed for Friday/Friday night as boundary sets up very close to 
southern County Warning Area and this far out confidence on this position is very 
low given recent model performance. If correct this trend would 
suggest cooler temperatures at or just below climatology by next weekend. 
Conservative cooling is in the forecast at this time despite better 
than average agreement among GFS/ensemble/ECMWF due to 
aforementioned potential for large model error.&& 


&& 


Iwx watches/warnings/advisories... 
in...none. 


Michigan...none. 


Ohio...none. 


Lm...none. 


&& 


$$ 


Short term...T 
long term...lud 
aviation...T