Quoting a research note issued by Piper Jaffray’s Gene Munster to clients this morning, BusinessInsider reports the Mac platform has seen a terrific rise in sales during the first quarter of 2011 in the United States. By summarizing data from NPD, the report details how the release of the new MacBook Pros in late February drove a 47% increase in sales year-over-year in the month of March, with an average 27% growth in the first quarter.

That 47% uptick followed growth of 20% in January and 12% in February, for average of 27% over the first quarter of 2011. That stands in stark contrast to the 3.2% drop in worldwide sales reported last week by IDC.

Bottom line: Munster expects Apple (AAPL) to report Mac unit sales in the range of 3.6 to 3.7 million, ahead of the Street’s consensus of 3.6 million.

So while the worldwide PC industry was seeing a serious decrease in sales in Q1 2011, Apple apparently managed to achieve a 27% growth with (allegedly) high Mac sales in the US. Like previous reports suggested, however, overall iPod sales should be down from last year – quite possibly because of the media playback capabilities of iPhones and iPads.

Analysts polled by Fortune two weeks ago claimed Apple could have sold nearly 4 million Macs in the second fiscal quarter of 2011 (which ended on March 26). Apple is set to announce the Q2 2011 financial results on April 20th.