Every year, when paying my taxes, I typically get a small amount back from the Feds, and usually pay "less than $400" to my state. However, within this 2016 year, I unexpectedly made a large amount of short-term capital gains day-trading on the stock market, let's say about $20k+, without filing any Form 1040-ES, or doing any special withholding beyond what my employer withholds. So I had to pay thousands in short-term capital gains taxes at the end of the year, but I believe I met an exception of it being unexpected when filing, at least just for this year alone, so I don't think I will be penalized (beyond normal taxation).
However, next tax year (2017), say if I theoretically owe the Feds+state tens of thousands of dollars worth of short-term gains taxes again (come up short on estimated withholding), which is not my normal expected income, would I be penalized? I read something about filing form 1040-ES, but this is unexpected income and I can't predict the future, in fact I could lose -20k during 2017. If I do need to pre-pay/withhold/estimate, is there anyway to pay Uncle Sam money immediately after every Short-Term sale?