Traders work on the floor at the New York Stock Exchange, August 5, 2019. Brendan McDermid | Reuters

Here are the most important things to know about Monday before you hit the door.

1. Crazy quarter ends

The third quarter winds down on Monday, concluding a volatile period of three months on Wall Street. The S&P 500 and the Dow Jones Industrial Average are set to finish the quarter up only slightly, rising 0.6% and 0.8% respectively through Friday's close but those modest figures do not tell the full story. The Dow suffered its worst day of the year on Aug. 14 when the yield curve inverted. Big declines were seen throughout the month of August as President Donald Trump escalated his trade war with China. For the month ahead, investors should be prepared for another bumpy ride as October has historically been the most volatile month, Goldman Sachs warned.

2. Key market faces big test

The repo market could face strong demand on Monday as banks pull back on lending to spruce up their balance sheets to closeout the quarter. The Fed has used overnight and 14-day market operations to stabilize the repo market, used by financial institutions to fund themselves on a short term basis. The Fed was reacting to a sudden spike in rates Sept. 16 and 17, and it is under pressure to permanently resolve the issue, which seems to stem from a cash crunch in the overnight borrowing market, rather than a credit crisis. There should also be high demand on Monday due to cash needed related to the settlement of $113 billion in Treasurys, auctioned Tuesday, Wednesday and Thursday.

3. Trade war escalates