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fxus63 kind 130448 
afdind 


Area forecast discussion 
National Weather Service Indianapolis in 
1148 PM EST Tue Dec 12 2017 


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


&& 


Synopsis... 
issued at 332 PM EST Tue Dec 12 2017 


Clipper systems will bring chances for precipitation Wednesday and 
again Friday and reinforce below normal temperatures. After that 
a warmup will arrive for the weekend, followed by more precip 
chances to end the weekend and start next week. 


&& 


Near term /overnight/... 


Issued at 951 PM EST Tue Dec 12 2017 


Surface analysis shows quick northwest flow in place across Indiana with 
a surface ridge over Illinois. Tight pressure gradient across the 
area was resulting win steady winds. Of note were very dry dew 
points in the single digits. This has resulted in temperatures 
already falling into the teens at many locations. Satellite 
imagery shows limited cloud cover over northern Illinois and 
Northeast Indiana...with much of central Indiana clear. Thus have 
trended lows a few degrees cooler than the previous forecast given 
the quick cooling progress we have made this evening and the low 
dew points. No other significant changes. 


&& 


Short term /Wednesday through Friday/... 


Issued at 332 PM EST Tue Dec 12 2017 


Forecast focus is on precipitation chances for Wednesday/Wednesday 
night with a clipper system again moving through the Great Lakes. 
Models are in fairly good agreement on the upper wave not 
bringing any chances for precipitation into the forecast area 
until at least late morning if not the afternoon. Warm advection 
will take place during the morning across most of the area ahead 
of the clipper, and this should allow the column to warm with 
temperatures reaching into the 40s for the southwestern half or so 
of the area, and mid to upper 30s over the remainder. Thus as 
forcing from the clipper arrives, some of the area will likely 
seeing rain or a mix of rain and snow. Also, the column looks 
fairly dry to start the day, and it could take some time to reach 
saturation for precip to make it to the surface. Expect to see 
some cooling with precip onset for this reason as well. Thus even 
spots that see rain initially could change over to a mix rather 
quickly, especially in the northern half or so of the area. With 
warmer temperatures to start though and some warming of the ground 
amounts will be light. The highest snowfall totals will be in the 
northeast where precip will likely remain snow the entire time. 
Looking at around an inch to perhaps an inch an a half in isolated 
parts of the northeastern counties. Northeast of indy could see a 
couple tenths to half an inch, with accumulation unlikely west 
and south of I-74. Snow will continue over the far northeast 
counties til midnight or so and this could have some lake 
enhancement. 


By Thursday morning dry weather will again be the rule until 
Friday, when another system could bring some small chances for 
snow back to the area. At this time accumulations look very 
minimal. Temperatures will run below normal through the short 
term. 


&& 


Long term /Friday night through Tuesday/... 


Issued at 332 PM EST Tue Dec 12 2017 


Friday night will begin the weekend a little cold with snow on its 
way away from the area and only a slight chance for snow over the 
eastern counties early. After that models are in agreement on the 
upper pattern turning warmer and dry for most of the weekend with 
upper ridging building over the area. Highs in the 40s and lows in 
the upper 20s to low 30s can be expected. Starting Sunday 
afternoon another upper trough begins to approach the area and 
this will bring increasing chances for precipitation for parts of 
the area. Models are showing more of a spread with the timing of 
this next troughs approach and passage though, so low confidence 
on timing of precipitation, and lower than normal confidence for 
Monday through Tuesday temperatures. Prior to that, high 
confidence in temperatures for the weekend and dry conditions 
going into Sunday. 


&& 


Aviation /discussion for the 130600z tafs/... 


Issued at 1150 PM EST Tue Dec 12 2017 


VFR conditions are expected to continue overnight and 
through 18z Wednesday. 


Quick northwest flow will remain in place overnight. Satellite shows some 
mid and high cloud over Northwest Indiana poised to stream across ind and 
laf within the next 1-3 hours...however...surface ridging should 
build east and allow unlimited ceilings for much of the overnight. 


A short wave and associated cold front will push across Indiana 
after 18z Wednesday. This will result in some snow showers and VFR 
ceilings eventually becoming MVFR ceilings in the wake of the cold front. 
Time heights and forecast soundings show saturated lower level in 
the wake of the front for Wednesday evening. 


&& 


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


$$ 






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