Treasury Secretary Jack Lew warned Congress in a letter Wednesday morning that Oct. 17 will be the last day that the government has the funds to meet all its obligations if the debt ceiling is not raised.

That is within the range Lew has previously indicated, and in line with projections from outside analysts. But now Congress has a specific deadline. If it does not act before Oct. 17, a Thursday, the government risks defaulting on the debt, an outcome that Lew warned "could be catastrophic."

Lew previously said that the Treasury would exhaust the extraordinary measures it has used to create headroom under the debt limit by mid-October, at which point it would have only $50 billion in cash on hand and whatever revenues come in on a given day with which to pay the government's bills.

But now Lew is cautioning that the department will have only roughly $30 billion on hand after the 17th. Daily net expenditures can be up to $60 billion, according to Lew.

Lew has been trying to raise the level of concern about the looming debt ceiling deadline. On Tuesday, he warned investors that they were not sufficiently worried about the possibility that Congress would not reach a deal to raise the limit in time.

The government hit the roughly $16.7 trillion statutory debt ceiling in May. Since then, Lew has taken a number of steps to free up funding without increasing the amount of public debt.