NEW YORK (TheStreet) -- Western Digital (WDC) - Get Report is the top gainer in the S&P 500 today following Wednesday night's first-quarter earnings report.

The stock opened the day with a huge upside gap that lifted shares more than 8%. Western Digital has moved higher since the bell, and at midday was stabilizing with a 10% gain. Volume powering today's surge will mark the heaviest positive session for the stock since November of 2013.

Today's very bullish action is a sharp change in character for Western Digital. The stock has been struggling all year and, despite a 10% gain today, is still working on its seventh straight lower monthly high. At last week's low, Western Digital was more than 33% below its 2014/2015 highs as the massive selling wave that hit shares in late June ran its course.

A JPMorgan downgrade on June 23 sparked the flush that drove Western Digital to a deeply oversold reading as July began. As the downside momentum began to ease in early July, Western Digital quickly entered basing mode.

During July, Western Digital has posted 10 days of above-average positive volume. Investors haven't shown interest that strong since mid-2013. The stock remained in a tight range during this healthy basing action.

Heading into earnings, the bulls stepped in again after four days of light chop. Investors were showing a great deal of confidence yesterday as well, pushing upside volume to its heaviest level since early February.

This momentum will likely carry shares higher in the near term, but a very heavy resistance area near $90 will be difficult to clear. A pullback following a test of major supply near the May/April lows will provide a low-risk entry opportunity. In the meantime, Western Digial has a solid layer of support in place near $82. The stock's initial July high is here.

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This article is commentary by an independent contributor. At the time of publication, the author held no positions in the stocks mentioned.