Stock Quotes in this Article: ACOM, ACOR, ITMN, MRVL, PLXS, STX, ULTA, SODA

 WINDERMERE, Fla. (Stockpickr) -- Professional traders running mutual funds and hedge funds don’t just look at a stock’s price moves; they also track big changes in volume activity. Many times when above average volume moves into equity it precedes a large spike in volatility.

Major moves in volume can signal unusual activity, such as insider buying or selling -- or buying or selling by “superinvestors.”

>>5 Big Stocks to Trade for Gains

Unusual volume can also be a major signal that hedge funds and momentum traders are piling into a stock ahead of a catalyst. These types of traders like to get in well before a large spike, so it’s always a smart move to monitor unusual volume. That said, remember to combine trend and price action with unusual volume. Put them all together to help you decipher the next big trend for any stock.

Let's take a look at a number of stocks rising on unusual volume today. They are all recording volume in midday trading that is already at least 100% above their average trading volume for a full day.

Sodastream International

Sodastream International (SODA), along with its subsidiaries, is engaged in developing, manufacturing and marketing home beverage carbonation systems and related products. The stock is trading up 5.2% at $39.70 in recent trading.

Today’s Volume: 3.5 million

Average Volume: 1.4 million

Volume % Change: 296%

Shares of SODA are soaring higher today after the company said it has partnered with Kraft Foods (KFT) to make their branded flavors such as Country Time and Crystal Light available with its soda makers.

From a technical standpoint, SODA is gapping higher today and has broken out above some past overhead resistance at $36.96 with monster volume. Market players should now watch for a sustained high-volume move and close above $40.24 to $41.88 to trigger the next big breakout.

If SODA can manage to close near its daily high of $41.88, then look for a re-test soon of its 200-day moving average of $45.01. Volume today is already well above its average action of 1.4 million shares.

Ancestry.com

Ancestry.com (ACOM) is an online family history resource. The stock is trading up 15.7% at $26.42 in recent trading.

Today’s Volume: 2.1 million

Average Volume: 885,813

Volume % Change: 263%

Shares of ACOM are soaring today after the company reported a 22% jump in subscribers in 2011 and forecasted strong 2012 sales.

From a technical standpoint, ACOM has gapped up huge today and broken out above some near-term overhead resistance at $23.50 and $26 on monster volume. Traders should now look for continued upside as long as ACOM can close near its daily higher.

The next overhead resistance levels that will trigger a a href="http://stockpickr.com/breakout-trading-technical-analysis-primer.html?cm_ven=sptext"> breakout trade< will come into play at $27.84 and $29.34. Watch for a high-volume move above those levels that’s near or above 885,813 shares. If we get that action, then look for ACOM to re-test its 200-day moving average of $31.59.

Ancestry.com is one of the top holdings at Whitney Tilson's T2 Partners as of the most recently reported quarter.

Seagate Technology

Seagate Technology (STX) designs, manufactures, markets and sells hard disk drives. The stock is trading up 5.3% at $17.72 in recent trading.

Today’s Volume: 19.7 million

Average Volume: 10.45 million

Volume % Change: 289%

Shares of Seagate are jumping higher today after the company said its coming back from last year’s floods in Thailand. The company forecast revenue of $3.1 billion to $3.2 billion in the current quarter, versus Wall Street estimates of $2.81 billion.

From a technical standpoint, STX is flirting with a breakout trade today with the stock gapping higher towards its nearest overhead resistance level at $17.70. In earlier trading, STX hit $18.27, but it has since then pulled back to its current price of $17.80.

Traders should watch for a sustained high-volume move and close above $17.70 and then $18.60 to trigger a major breakout for STX. Look for volume that’s near or above 10.45 million shares. Volume today is well above that level, so watch for a close over $17.80 and near its daily highs.

Seagate, one of Greenlight Capital's holdings, shows up on a list of 10 Dividend Stocks to Keep You Safe Into 2012.

Acorda Therapeutics

Acorda Therapeutics (ACOR) is a commercial-stage biopharmaceutical company engaged in the identification, development and commercialization of therapies that improve neurological function in people with multiple sclerosis, spinal cord injury and other disorders of the nervous system. This stock is trading up 6.9% at $26.58 in recent trading.

Today’s Volume: 885,000

Average Volume: 447,002

Volume % Change: 229%

From a technical standpoint, ACOR has a href="http://stockpickr.com/breakout-trading-technical-analysis-primer.html?cm_ven=sptext"> triggered a major breakout< after the stock took out some overhead resistance levels at $24.08 and $25.45 (its 200-day moving average) with monster volume.

Market players should now watch for the next big breakout to trigger if ACOR can manage to trade above $26.79 to $27.26 with high-volume. Look for volume that’s near or above 447,002 shares to signal that ACOR wants to trend higher towards $30 to $32 in the near future.

Acorda shows up on a list of 13 Biotech Stocks Bought and Sold by Hedge Funds in the most recently reported quarter.

InterMune

InterMune (ITMN) is a biotechnology company focused on the research, development and commercialization of therapies in pulmonology and fibrotic diseases. This stock is trading up 11% at $14.61 in recent trading.

Today’s Volume: 4.2 million

Average Volume: 1.86 million

Volume % Change: 209%

Shares of ITMN are ripping to the upside today after the company said its new lung disease treatment Esbriet has generated about $2.8 million in sales since its mid-September launch in Germany.

From a technical standpoint, ITMN has broken out today above some near-term resistance at $14 on monster volume. This stock now has could now be setting up to make a run at its 50-day moving average of $18.27, since there’s almost no overhead resistance between its current price and the 50-day.

Traders should continue to look for long biased trades in ITMN as long as the stock closes near its daily highs and stays above $14 in the coming days or weeks.

InterMune shows up on a recent list of 5 Biotech Stocks for 2012.

Marvell Group

Marvell Group (MRVL) is a fabless semiconductor provider of application-specific standard products. This stock is trading up 5.6% at $14.99 in recent trading.

Today’s Volume: 16 million

Average Volume: 12.4 million

Volume % Change: 115%

Shares of MRVL are ripping today after the company said it is replacing Intel (INTC) as Google’s (GOOG) lead chip provider for their Google TV product.

From a technical standpoint, MRVL is flirting with a big breakout today if this stock can manage to close above some near-term overhead resistance at $15.17 with volume.

At last check, the volume today is already well above its average action of 12.4 million shares, so watch to see if MRVL can close above $15.17 and near its daily highs. If we get that action, then look for MRVL to make a run at $16 to $17 in the near future, or even potentially higher.

Marvell shows up on a list of 3 New Investment Ideas From Greenlight's Einhorn for the most recently reported quarter.

Ulta Salon Cosmetics & Fragrance

Ulta Salon Cosmetics & Fragrance (ULTA) operates a specialty retail stores selling cosmetics, fragrance, haircare and skincare products, and related accessories and services. This stock is trading up 5.4% at $69.98 in recent trading.

Today’s Volume: 1.5 million

Average Volume: 952,436

Volume % Change: 124%

Shares of ULTA are trading nicely to the upside today after the company boosted its fiscal fourth-quarter sales guidance and raised an already upbeat earnings target for the quarter, citing strong sales performance during the holiday period.

From a technical standpoint, ULTA has started to gap above its 50-day moving average of $69.05 today with heavy volume. Market players should now look for a sustained high-volume move and close above the 50-day to signal that UTLA wants to trend back towards its 52-week high of $75.70.

Look for UTLA to close near its daily highs of $71.43 to signal that this stock wants to re-test $75.70 in the near future. The last bit of overhead resistance before $75.70 sits right above $74.

Ulta is one of TheStreet Ratings' top-rated specialty retail stocks.

Plexus

Plexus (PLXS), along with its subsidiaries, provides optimized product realization solutions through a product realization value stream service model. This stock is trading up 8.3% at $29.86 in recent trading.

Today’s Volume: 401,000

Average Volume: 301,579

Volume % Change: 119%

Shares of PLXS are soaring higher today after the company said it will expand its manufacturing in Southeast Asia through a strategic arrangement with Kontron AG. Due to this new partnership, Plexus said it narrowed its revenue and earnings for the fiscal first quarter.

From a technical standpoint, PLXS has started to trigger a big breakout today now that this stock is moving above some past overhead resistance levels at $29.03 and $29.61 (its 200-day) with strong volume. Traders should now watch for a sustained high-volume move and close above those levels to signal that PLXS wants to trend significantly higher.

If we get that close today, then look for PLXS to make a run at $34 to $35 in the near future, as long as it clears its last overhead resistance hurdle at $30.45.

To see more stocks rising on unusual volume, including Zumiez (ZUMZ), Ascena Retail Group (ASNA) and Ross Stores (ROST), check out the Stocks Rising On Unusual Volume portfolio on Stockpickr.

-- Written by Roberto Pedone in Winderemere, Fla.

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At the time of publication, author had no positions in stocks mentioned.

Roberto Pedone, based out of Windermere, Fla., is an independent trader who focuses on stocks, options, futures, commodities and currencies. He is also an outside contributor to Beconequity.com and maintains the website Maddmoney.net, which he sold to Blue Wave Advisors in 2008. Roberto studied International Business at The Milwaukee School of Engineering, and he spent a year overseas studying business in Lubeck, Germany.