Intel Corp. warned third-quarter sales growth will be short of forecasts by 3% to 5%. The news sent its stock plummeting Friday and further aggravated market worries about the second-half outlook for PC sales. Some analysts expected third-quarter Intel sales gains of as much as 10%, but Intel cited weaker demand in Europe for its more cautious outlook. In intra-day trading Friday, Intel fell as much as 25% before closing at $47.94, off 16.65% for the week. Its fall also helped pull down the AdMarket 50 index, off 2.30% Friday.