Area forecast discussion 
National Weather Service Indianapolis in 
620 am EDT Wednesday Jul 30 2014 


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


&& 


Synopsis... 
issued at 251 am EDT Wednesday Jul 30 2014 


Central Indiana will continue to be under the influence of low 
pressure centered over eastern Ontario while a large ridge of high 
pressure resides over the western U.S. This pattern will result in 
slightly below normal temperatures through the period and daily 
chances for showers and isolated thunderstorms through the first 
half of the weekend. However...conditions will be dry for most of 
the extended as aforementioned ridge moves closer to central Indiana. 




&& 


Near term /today/... 


Issued at 251 am EDT Wednesday Jul 30 2014 


The main focus will be shower/thunderstorm chances /mainly this 
afternoon and evening/. 


Today will be the last day of the especially cooler than normal 
temperatures as central Indiana remains in northwest flow. Temperatures will top 
off in the middle to upper 70s which was captured well with a model 
blend. 


Today/S weather will be similar to yesterday/S...afternoon and 
evening shower/thunderstorm activity fueled by the broad low 
pressure system over eastern Ontario. Anticipate activity to be 
more widespread this afternoon though /across the northern 
counties/ as a trough at the surface increases lift after Wednesday 
18z...supported by weak enhancement in vorticity at 500 mb. 
So...will carry chance probability of precipitation over the northern half of central 
Indiana...slight chance over most of the south...and dry over the 
extreme southern counties. 




&& 


Short term /tonight through Friday night/... 


Issued at 251 am EDT Wednesday Jul 30 2014 


The main focus continues to be diurnal shower/thunderstorm 
development through the period. 


The low pressure system over eastern Ontario/James Bay will remain 
somewhat stationary through Friday...finally pushing off to the 
east on Friday evening. Perturbations in the upper flow will be 
just enough to trigger daily shower/thunderstorm activity with 
peak heating. However...will only carry slight chance probability of precipitation on 
Thursday since those perturbations will be limited. On Friday 
though...a more defined short wave is providing a decent vorticity maximum 
in the middle levels...which justifies carrying chance probability of precipitation across 
all of central Indiana. 


Central Indiana will break out of the northwest flow on Thursday 
and fall under more of a west/southwesterly flow...which will lead 
to a weak warming trend. Highs will climb back into the low 80s 
with lows in the low 60s. Models are in agreement with the 
changing pattern...so continued to use a blend. 




&& 


Long term /Saturday through Tuesday/... 


Issued at 251 am EDT Wednesday Jul 30 2014 


Long term focus will be on a potential change in the persistent 
cyclonic flow pattern that has kept it cool across the area. 


Extended models in decent agreement that the James Bay vortex will 
open up and become absorbed by the icelandic low by Saturday. 
Meanwhile...remnant broad upper trough will move east of central 
Indiana on Sunday with models in good agreement on decent subsidence 
across central Indiana. This should allow for the diurnal 
thunderstorm chances to end on Sunday with dry conditions until 
Monday as surface high pressure settles in. Finally...models hint 
that a cold front will be dropping down across the region in Tuesday 
in northwest flow aloft. This may bring a few more thunderstorms to 
the area per the regional blend. 


Regional blend has the right idea regarding rising temperatures 
as the persistent upper trough moves to the eastern states and 
dampens this weekend and early next week. Afternoon highs should be 
back in the 80s across all of central Indiana by Monday or earlier. 




&& 


Aviation /discussion for 301200z taf issuance/... 
issued at 620 am EDT Wednesday Jul 30 2014 


Any fog should be gone by 12z with patches of morning ac ahead of a 
weak upper wave in the cyclonic flow aloft. After 17z...with 
convective temperatures met...should see some diurnal VFR cumulus with 
thunderstorms possible mainly at ind and laf. Will go with thunderstorms in the vicinity 
through 23z there. Then...winds will become very light to calm 
tonight...and with little cloud cover could see some more MVFR or 
worse fog overnight. 


&& 


Ind watches/warnings/advisories...none. 


&& 


$$ 


Synopsis...tdud 
near term...tdud 
short term...tdud 
long term....mk 
aviation...mk 


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