After two avalanches last week, the Tahoe snowpack has started to stabilize according to Tahoe National Forest Sierra Avalanche Center forecasters. But that trend could reverse if the fast-moving storm predicted to hit the South Shore Tuesday brings another foot or more of fresh snow. The Sierra Avalanche Center, a nonprofit that provides daily avalanche advisories during the winter, recorded two human-triggered slides last week. A skier triggered a 700-foot-long avalanche on March 7 around 4 p.m. near Donner Summit, while a snowboarder caused another slide March 9 at Mount Rose that temporarily reduced traffic to one lane on the …