Area forecast discussion 
National Weather Service Indianapolis in 
548 am EST sun Dec 4 2016 


Update... 
the aviation section has been updated below. 


&& 


Synopsis... 
issued at 333 am EST sun Dec 4 2016 


An upper trough will move across central Indiana today bringing rain 
and some snow to the area. A stronger system will bring mainly rain 
to the area Monday night into Tuesday. Much colder air will move in 
mid week and could bring some snow with it. More snow is possible 
next weekend. 


&& 


Near term.../today/ 
issued at 333 am EST sun Dec 4 2016 


Isentropic lift will increase across central Indiana today as an 
upper level wave moves into the area. Q-vector convergence progs 
show decent forcing as well. Moisture looks good. Thus expect the 
area to see precipitation today. Went categorical pops all areas. 


Timing of the best forcing and moisture is this afternoon, so that 
is when pops will be highest. For the early to mid morning, dry low 
levels will eat away at precipitation that develops across the area. 


Main problem is precipitation type across the northwest forecast 
area today. Temperatures will be cold enough this morning for any 
precipitation that reaches the ground to be a mix of snow and rain 
across much of the area, with snow more favorable northwest where 
temperatures will be coolest. 


Across the far northwest (warren, and northwest portions of 
Tippecanoe and Carroll counties), temperatures will struggle to get 
above the mid 30s. Forecast soundings show temperatures remaining 
below freezing for all but the near surface layer. 


Unfortunately even a small change in forecast temperatures could 
have big impacts on precipitation type there. For now feel that 
readings will be cold enough for perhaps around 1 inch of snow today 
in the extreme northwest. Will have to watch closely. 


Elsewhere mostly rain is expected so little or no snow accumulation 
is expected. 


&& 


Short term.../tonight through Tuesday night/ 
issued at 333 am EST sun Dec 4 2016 


Models are close enough that the superblend initialization 
was accepted for most items. 


Dry air will work in quickly tonight behind the departing upper 
trough. Went low pops during the evening, with most of the area dry 
by midnight. Temperatures may cool enough for some snowflakes to mix 
in across the north before precipitation ends. 


High pressure will then build in briefly for Monday. However, lift 
will increase Monday night as an upper low approaches the area from 
the southwest. This system will have good forcing as the upper 
system moves across, including pretty good frontogenetical forcing. 
Will go likely to categorical pops by Tuesday morning. Pops will 
quickly lower Tuesday afternoon as the system exits. 


Temperatures might be cold enough for some snow to mix in with the 
rain Monday night as the system moves in. However, readings should 
warm enough for all rain by late Monday night. 


&& 


Long term /Wednesday through Saturday/... 
issued at 333 am EDT sun Dec 4 2016 


Ensembles suggest the main weather feature during this period will 
be a short wave trough that is expected to push across the Great 
Lakes around Wednesday into Thursday. Will go with chance pops for 
Wednesday night into Thursday morning to cover this feature. 
Ensembles suggest snow will be the predominate precipitation type 
with this system, although some mixed precipitation possible 
Wednesday evening over the southern and eastern zones. Light 
accumulations are possible. 


Next upper trough is expected to move into the middle of the country 
by next Saturday, although timing and location differences are large 
at this time. Ensembles suggest some snow is possible within the 
warm advection pattern ahead of this trough by next Saturday. Will 
go with chance pops at that time. 


&& 




Aviation (discussion for the 041200z taf issuance)... 
issued at 548 am EST sun Dec 4 2016 


Conditions expected to deteriorate to IFR and LIFR during the course 
of the day and then generally remain IFR during the night. Mixed 
rain/snow is possible, especially at klaf. 


Patchy light rain, with some light snow perhaps mixed in, will move 
into the area during the first six hours of the taf period. 
Widespread precipitation is expected through the afternoon. A 
rain/snow mix is possible anywhere this morning, with mainly rain 
this afternoon (except for klaf where a mix may continue). 
Precipitation will end by early evening. 


Conditions will deteriorate into IFR/LIFR with the widespread 
precipitation. IFR ceilings will likely continue tonight after 
precipitation ends. 


&& 


Ind watches/warnings/advisories... 
none. 
&& 


$$ 


Synopsis...50 
near term...50 
short term...50 
long term....jas 
aviation...50 



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