Area forecast discussion 
National Weather Service Indianapolis in 
108 PM EDT Wednesday Oct 1 2014 


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


&& 


Synopsis... 
issued at 242 am EDT Wednesday Oct 1 2014 


Quiet weather is expected today before a few active weather days 
conclude the work week. 


High pressure over the Great Lakes is expected to depart to the 
east today...providing one last day of quite pleasant weather. A 
warm front ahead of an area of low pressure will arrive in central 
Indiana on Thursday morning...and may bring a few showers to the 
area on Thursday morning. In the wake of warm front...warm 
southerly winds will push a very warm and more humid air mass into 
central Indiana by Thursday afternoon. 


As low pressure then pushes north of Indiana on Thursday night and 
Friday...the low will drag a cold front across Indiana. This will 
result in some showers and perhaps a few thunderstorms. 


In the wake of the cold front...much colder air will arrive in 
central Indiana for the weekend...pushing temperatures to below 
seasonal normals. 


&& 


Near term /today/... 
issued at 1233 PM EDT Wednesday Oct 1 2014 


Going forecast has been in relatively good shape through the 
morning...with minor tweaks required for satellite trends...mainly 
the persistence of the stratus to the northeast through the morning. 
Some minor temperature tweaks made but again...generally forecast in good 
shape. Previous discussion follows. 


Issued at 242 am EDT Wednesday Oct 1 2014 


Surface analysis early this morning shows high pressure in place 
over the Great Lakes. Low pressure was found over the upper 
Midwest. Skies were mostly clear across central Indiana and dew 
points were in the comfortable middle to lower 40s. Temperatures 
ranged from the low 40s across the northeast...43 in Muncie at 
this time!...to the upper 50s southwest. Water vapor showed a 
ridge of high pressure aloft over the Great Lakes with subsidence 
in place over Indiana. 


GFS and NAM continue to suggest that the high pressure system and 
ridge aloft will slowly move east today and begin to exit the 
area. Forecast soundings and time height sections remain quite 
dry. Forecast soundings show convective temperatures in the lower 
80s today...some so isolated cumulus cannot be ruled out...particularly 
across the south. Thus will aim for a mostly sunny day. 


As for temperatures...weak warm air advection is expected as thicknesses 
rise slightly along with 850mb temperatures. Surface flow also begins a 
more southeasterly component. Thus will trend highs slightly 
warmer than persistence which will be a good blend between the 
mavmos and metmos. Metmos is notably too cold across the east 
and northeast. 


&& 


Short term /tonight through Friday night/... 
issued at 242 am EDT Wednesday Oct 1 2014 


Active weather pattern begins tonight as the GFS and NAM suggest a 
warm front arriving toward 12z Thursday. Time heights and forecast 
soundings show saturation beginning in the lower levels late 
tonight amid weak lift. 305k GFS isentropic surface shows a surge 
of specific humidities over 7 g/kg with good lift. Lower level q 
vectors are a bit more marginal...showing best convergence farther 
west. Upper support appears marginal as a weak wave appears to be 
ejected out of the broader...deeper short wave to the west. Thus 
will keep the forecast dry during T he evening hours and keep a 
low chance probability of precipitation for a shower toward 12z due to lower level moisture 
and possible isentropic lift. As for temperatures will trend lows warmer 
than mavmos given the warm air advection and southerly flow. 


GFS and NAM suggest that Indiana will be firmly in th warm sector 
on Thursday...and after any morning clouds and isolated showers 
depart some good heating should occur as warm air is advected 
into the area on southerly winds. GFS 305 isentropic surface shows 
good moisture pushing through the area over the course of the day 
and forecast soundings show saturation aloft. Thus will stick 
close to the mavmos probability of precipitation as lingering precipitation will be possible in 
the morning and an afternoon showers amid the warm and humid air 
mass cannot be ruled out. Given the warm air advection..but 
expected clouds and possible precipitation will trend highs cooler than 
mavmos. Still middle 80s across much of central Indiana looks 
reasonable. 


Models agree that the strong cold front will push across the 
forecast area late Thursday night and early on Friday. Strong 
forcing will be place aloft as the models suggest a deep trough 
will be pushing out of the Central Plains toward the Ohio Valley. 
Plenty of moisture looks to remain in place due to the warm and 
southerly flow ahead of the system. 305k isentropic surface shows 
specific humidities in excess of 6 g/kg. By 12z Friday...forecast 
soundings show deep saturation with precipitable waters  over 1.50 inches. Thus 
will will trend probability of precipitation higher on Thursday night and Friday as all of 
these features pass through. Given the expected clouds...rain and 
cold air advection will expect steady or slowly falling 
temperatures through the course of the day on Friday. 


On Friday night...much dryer air arrives aloft as the cold front 
passes and strong cold air advection will be in place the 
deepening low over the Great Lakes a strong pressure gradient 
looks to be in place resulting in gusty west winds as 850mb temperatures 
fall to below 0c by 12z Sat. Aloft strong forcing remains in place 
as a deep upper trough pushes into the Ohio Valley. Moisture will 
remain aproblem...however...cannot rule out any wrap around 
precipitation at this point given the strong dynamics. Thus will stick to 
low chance probability of precipitation. Will trend lows at or below mexmos lows. 


&& 


Long term /Saturday through Tuesday/... 
issued at 242 am EDT Wednesday Oct 1 2014 


Ensembles indicate that a deep progressive upper trough will be 
passing off to the east at the beginning of the extended. Could be 
some light instability showers or sprinkles on Saturday with 850mb 
temperatures prognosticated to be near or below freezing. However...given 
the local area will be under the subsidence region of the upper 
trough...think the threat for measurable precipitation is still too 
low to mention at this point. Will keep Saturday dry for now. 


Otherwise...ensembles suggest another upper disturbance will drop 
into the area around Sunday and Monday. Will go with chance probability of precipitation at 
those times. Long range operational models suggest some convective 
potential with this system. 


By next Tuesday...upper flow may tend to flatten out as heights 
begin to rise. Will go dry for next Tuesday. 


&& 


Aviation /discussion for the 011800z tafs/... 


Issued at 1259 PM EDT Wednesday Oct 1 2014 


Some limited diurnal cloud based 030-040 should develop later 
this afternoon...especially over the more southern taf sites. 
Light surface winds less than 8 knots. Increasing clouds early 
Thursday ahead of the next system. Mentioned vcsh 16-18z Thursday for 
all the taf sites save for kbmg. 


&& 


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


$$ 


Synopsis...puma 
near term...puma/nield 
short term...puma 
long term...jas 
aviation...smf 


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