M4, the 135-m tower in the SE corner of the NWTC, will be out of service for the winter 2015-2016. M5 (the other 135-m tower) and M2 (80 m) will remain in operation.
Data from M4 from 2012 -2015 are still available online at [url]National Wind Technology Center's Information Portal | Wind Research | NREL. Historic data from M5 and M2 can also be found at that URL.
Current conditions from M5 are available at [url]National Wind Technology Center's Information Portal | Wind Research | NREL. M2 data can be found at [url]http://www.nrel.gov/midc/nwtc_m2/display/[/url].