We've brought the Heroes of the Storm service down for a period of extended maintenance today in order to release a brand new patch for the Technical Alpha. Maintenance is ongoing, but don't worry; we'll let you know as soon as the Nexus is back online in this forum thread. In the meantime, you can check out complete patch notes below.

Update (December 10, 2014): We released a follow-up patch in order to fix a few bugs and add Stimpacks to the Heroes of the Storm in-game Shop. The December 10 updates have been added to the Shop and Bug Fixes sections of the patch notes below.