Area forecast discussion 
National Weather Service Indianapolis in 
531 PM EST Wednesday Nov 26 2014 


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


&& 


Synopsis... 
issued at 250 PM EST Wednesday Nov 26 2014 


A clipper system will bring chances for snow to mainly southwestern 
sections of central Indiana tonight. Warmer air will return to the 
area this weekend along with chances for rain. A couple of cold 
fronts will keep chances for rain at times early next week...but 
temperatures will be seasonable. 


&& 


Near term.../rest of this afternoon and tonight/ 
issued at 250 PM EST Wednesday Nov 26 2014 


One area of low clouds should continue to clear out to the 
northeast...but clouds associated with an approaching clipper system 
will quickly increase from the west by late afternoon. 


The clipper system and associated upper trough will weaken as they 
move southeast into the Ohio Valley tonight. Q-vector convergence 
plots show decent forcing...but most of the forcing will be to the 
south of the forecast area. 


Moisture is limited to the north of the system...and there will be a 
sharp cut-off to the precipitation. Based on latest trends and short 
term model forecasts...have decided to confine probability of precipitation tonight to the 
southwest third or so of the forecast area. 


Went likely probability of precipitation across the extreme southwest quickly tapering to 
slight chance probability of precipitation to the northeast. Probability of precipitation will diminish after late 
evening as the system moves off to the east. 


Forecast soundings show most of the column below freezing with only 
the near surface layer above freezing. Went mainly snow for the 
precipitation type...but did include a possible mix with rain across 
the far southwest early tonight to account for the initially warm 
air. Any accumulation should remain below 1 inch...with highest 
amounts in the extreme southwest forecast area. 


Otherwise went with a model blend for low temperatures under mostly 
cloudy skies. These temperatures are near MOS values. 


&& 


Short term.../Thanksgiving through Saturday/ 
issued at 250 PM EST Wednesday Nov 26 2014 


Focus is on any chance for precipitation through the period. In 
general models are close enough that a blend can be used. 


Early on Thanksgiving an upper trough will move across the lower 
Great Lakes. Some weak forcing from this upper trough could generate 
a few flurries across the eastern forecast area. During the 
afternoon flurries will remain possible across the far northeast due 
to the influence of Lake Michigan as colder air flows in behind the 
upper trough. 


Skies look to be mostly cloudy during the morning with perhaps some 
partial clearing across the southwest forecast area as drier air 
tries to work in. For temperatures stuck with a model blend. 


High pressure will move in Thursday night ending any flurries. With 
some partial clearing and a cold airmass in place...readings should 
dip into the teens in many areas. However did not go quite as cold 
as mav MOS would suggest given some clouds. 


Warm advection on late Thursday night into Friday will increase the 
clouds once again but moisture is limited enough to keep a dry 
forecast. Stuck with the model blend for temperatures. 


By Saturday a strong push of warm air will move into the area along 
with increasing low level moisture. Forcing looks too weak for 
organized precipitation...but looks like there could be enough lift 
for some sprinkles by Saturday afternoon. 


&& 


Long term /Saturday night through Wednesday/... 


Issued at 203 PM EST Wednesday Nov 26 2014 


GFS and European model (ecmwf) continue to suggest a quick moving cold front to 
sweep across the Ohio Valley on late Saturday and early Sunday. 
Best forcing remains far north of Indiana and flow aloft appears 
zonal...thus confidence in this event is low. 


European model (ecmwf) then shows high pressure building out of the upper Midwest 
into the Ohio Valley at the surface with the quick zonal flow 
aloft into the middle of next week. A lingering surface boundary 
appears to stick close to the Ohio River according to the GFS and 
the result is some chance probability of precipitation in superblend. Again confidence in 
precipitation continues to be very low as moisture and forcing appear 
lacking overall. 


Finally the European model (ecmwf) again suggests another moisture starved cold 
front will sweep into the Ohio Valley on Tuesday night into 
Wednesday. Again best forcing appears well north of the Great 
Lakes and again confidence is low. 


Of note through this period of the forecast is the mostly zonal 
flow aloft...which should lead to near normal or only slightly 
below normal temperatures. 


&& 


Aviation /discussion for the 270000z tafs/... 
issued at 531 PM EST Wednesday Nov 26 2014 


Weather disturbance currently causing widespread IFR/patchy LIFR 
conditions in snow over Illinois is expected to drop southeast 
tonight. Short term models suggest the northern fringes of this 
system will probably affect khuf/kbmg later tonight with a period of 
light snow...roughly 270400z-270800z. Confidence is low that snow 
will be heavy enough to result in prolonged IFR visibility 
restrictions...so will keep visibility restrictions above IFR for 
now. 


Otherwise...extensive MVFR ceilings 015-020 off to the north and 
northwest of the local area should advect back into the area from 
north to south later tonight as low level flow becomes northerly. 
These ceilings expected to linger beyond 271200z. 


Initially light surface winds should back around to 350-020 degrees 
at 6-8 kts by late evening...and eventually around to 310-330 
degrees by sunrise Thursday. 


&& 


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


$$ 


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


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