The U.S. budget deficit shrank to a six-year-low $486 billion in the just-ended fiscal 2014 from $680 billion in 2013, the Congressional Budget Office said Wednesday.

But while the fiscal storm that struck six years ago has subsided, the apparent calm is deceptive.

This year's deficit is expected to be near the low-water mark. Though next year's red ink could be slightly smaller, CBO projects a $556 billion deficit in 2016, rising toward $1 trillion in 2024 amid soaring entitlement and debt-service costs.

From a big-picture perspective, the deficit has shrunk because tax revenue has surged — more due to economic recovery than tax hikes — as spending has been held in check.

Tax receipts rose an estimated $239 billion, or 8.6%, in 2014, while total outlays rose by $44 billion, or 1.3%.

The progress in erasing the trillion-dollar deficits of President Obama's first term has been aided by financial-crisis interventions and Federal Reserve quantitative easing — to the tune of about $150 billion last year.

Government-seized mortgage giants Fannie Mae and Freddie Mac sent $74 billion to the Treasury in fiscal 2014. The Fed chipped in about $100 billion in its interest earnings to Treasury, or about $75 billion more than in pre-crisis times. Those payments are set to shrink in coming years.

The falling budget deficit also reflects efforts to rein in discretionary outlays — military spending fell by $30 billion, or 4.9%, last year. Meanwhile, an improving job market and the end of emergency jobless benefits cut unemployment insurance spending by $24 billion, or 34%.

Yet despite sequestration's spending restrictions and continued recovery in tax revenue, budget progress is about to grind to a halt and gradually reverse.

One reason is the ramping up of spending on ObamaCare. Exchange subsidies cost the government just $13 billion with the troubled launch that occurred in the second quarter of the fiscal year. In fiscal 2015, that's projected to rise to $50 billion.

The cost of Social Security and the major health entitlements (Medicare, Medicaid and ObamaCare) are expected to rise from 10% of GDP in 2013 (pre-ObamaCare) to 12.2% in 2024.

Over the same period, as interest rates normalize, the cost of servicing that debt will soar from 1.3% of GDP in 2014 to 3% in a decade, according to CBO.

The CBO assumes discretionary spending will fall to a decades-low 5.2% of GDP in 2024 from 7.2% in 2013.

Given the long-awaited entitlement spending storm that is brewing, an extra fiscal burden from surging debt-service costs won't be sustainable for long.

That's why the easing of the budget deficit to 2.8% of GDP in 2014 isn't cause for relief. It's only enough progress to stabilize debt levels at about 74% of the economy, not enough for bloated debt levels from the financial crisis to begin to recede.

In 2024, net interest outlays are expected to reach $799 billion, easily exceeding defense outlays of $716 billion.

From there, the budget debacle would accelerate, according to CBO's Long-Term Budget Outlook. From 2024 to 2034, public debt would surge from 78% of GDP to 96% of GDP as the deficit hits 6.2% of GDP and interest spending rises to 4.4% of GDP.

The fiscal outlook isn't as grim as it once was because the projected rate of health care spending growth has slowed markedly due to some hard-to-gauge combination of the weak recovery and ObamaCare's influence. But the trend still isn't looking good.