Not around Huaraz but still (and more) northern Peru is Lambayeque Region, where Chiclayo city is, and that's where the Seņor de Sipan was found. The famous Tumbas Reales (Royal Tombs) museum contains a beautiful and interesting collection of treasures from that finding.

If you are interested in this, I suggest you go to Trujillo (La Libertad region), where there are several archeological sites too (Huaca de la Luna, gorgeous!!, Dama de Cao, huaca el Brujo). Actually the idea is to do the MOCHE route. The Moche is the culture where the the Seņor de Sipan belongs to.

Check this info:
La ruta Moche

And mid may is good weather for visiting Chiclayo and Trujillo. You may find sunny days, specially in Chiclayo, and the heat is not so strong.