U.S. economic output accelerated to a 2.3 percent annual rate in the second quarter, slightly short of the expectations of government officials and investors hoping for a strong rebound from the economic contraction during the winter.

The inflation-adjusted gross domestic product number reported by the Bureau of Economic Analysis Thursday morning was below the 2.9 percent seasonally-adjusted annualized growth rate expected by Wall Street.

It was a significant improvement, however, from the first quarter, which saw revised growth of 0.6 percent. Before the revisions included in Thursday's release, the Bureau had estimated that the economy shrunk at a 0.2 percent rate in the first quarter.

While the erasure of the first quarter contraction was good news, the overall record of the past three years of the recovery took a significant hit Thursday, as revisions for the past three years marked down growth.

From the fourth quarter of 2011 to the first quarter of 2015, GDP growth was just 2 percent, rather than the 2.2 percent previously estimated. In other words, the recovery, already the weakest of the post-World War II recoveries, was even weaker than previously thought.

The Bureau revised the past three years' growth to reflect new and better source data, especially related to government refundable credits. It also reflected tweaks to the methodology used to tally total spending.

Thursday's release will reassure officials in the Obama administration and private investors that the economy is not close to slipping back into a recession, a possibility raised by the previously estimated first-quarter contraction. The slightly lower than expected rebound will also likely encourage Federal Reserve officials as they determine whether and when to raise interest rates this year, after keeping the short-term rate target near zero since 2008.

Thursday's second quarter growth statistic is an initial estimate and is subject to significant change in the months ahead. Growing personal spending, exports, state and local spending, and home-buying drove growth in the month. Federal government spending and imports put a drag on faster growth.

Of particular reassurance to Janet Yellen and other Fed economists will be the signs from Thursday's report that the negative effects holding down growth in the first quarter are indeed largely "transitory," as they have asserted.

Drag on U.S. net exports from the strong dollar appears to be waning. Net exports added 0.13 percentage points to growth in the second quarter, after subtracting nearly two percentage points the quarter before. Exports, which add to the GDP calculation because they involve American businesses getting paid for shipping abroad, grew five percent. Imports, which subtract also grew, but at a slower rate than earlier in the year.

Some items of spending that can be affected by unusual weather, such as auto sales and restaurant spending, also picked up in the second quarter.

It's possible that Thursday's report, in addition to being subject to future revisions, understated growth in the quarter. One measure of economic output that strips out volatile components, final sales to private domestic purchasers, grew at 2.5 percent for the quarter. The metric sums up consumer spending and private investment and excludes private inventories, net exports, and government spending.

The Bureau of Economic Analysis will release the second estimate for second quarter growth on August 27th.