Starting day three of the second four-day game on 45, Tasmania's Weatherald powered to 183 in a magnificent 275-ball innings punctuated by 16 fours and two sixes.
His knock - and an unbeaten 121 from captain Jason Sangha - took Australia from 1-76 on the resumption to a strong 3-379 by stumps on Tuesday, in reply to Sri Lanka A's 6-485 declared.
With the Darwin pitch ideal for batting the chance of a result looks slim, with the series poised to end 0-0 after game one finished in a stalemate.
Most discussion out of the match, then, may centre on Weatherald after the 30-year-old made hay on the Marrara Cricket Ground pitch to score his 13th first class century.
Coming after his 54 in his only innings in game one, the knock was a timely reminder to national selectors as they weigh top order options for this summer's home Ashes after a bleak tour of the West Indies for openers.
Usman Khawaja has averaged 15.37 through eight Test innings this calendar year and will turn 39 during the Ashes.
The 19-year-old Sam Konstas fared even worse when recalled to partner Khawaja in the recent 3-0 Test series romp in the Caribbean, averaging 8.33 and looking well short of the finished article.
Nathan McSweeney - dropped after averaging 14.40 through his first three Tests last summer against India - made 94 for Australia A last week to push his case for a possible recall, but failed on Monday in the second match, making 12.
Into calculations for a top-of-the-order Test debut in the Ashes comes Weatherald, who opened for Australia A and raised his ton on Tuesday off 146 deliveries, scoring in virtually every part of the ground.
The left-hander is coming off the finest summer of his career, in which he topped the Sheffield Shield competition with 905 runs.
His three tons - as with his effort on Tuesday - showed his capacity to push on to make a big hundred, scoring 186 against Queensland, 155 against Victoria and 145 against NSW.
On Tuesday, he and Kurtis Patterson took their second wicket partnership to 134 before Patterson was caught at point for 59 reaching for a wide delivery from paceman Asanka Manoj.
Weatherald and Sangha piled on 209 for the third wicket before Weatherald was bowled by off-spinner Nuwanidu Fernando.
