Less than a week ago, many of us were walking around outside in short-sleeve shirts and enjoying the warm spring weather as temperatures soared into the low 70s in northern New Jersey and into the summer-like 80s in our central and southern counties. A few days later, we had freeze warnings and frost advisories as morning temperatures plunged into the upper 20s to low 30s. And for three straight days, we’ve had lots of clouds and afternoon temperatures stuck in the chilly 50s — when they should be in the mid-60s. And more freeze advisories have been issued for overnight Wednesday into early Th…