Zones / 3a

Zone 3a

In the 2023 PRISM ZIP table, zone 3a is labeled with an average annual extreme minimum of -40°F to -35°F. 5 ZIP codes carry that half-zone. USDA’s map page describes these bands as 5°F half-zones inside 10°F zones.

None of the cities on this site fall in zone 3a. ZIP lookups still use it where the PRISM file says so.

Source: PRISM 2023 PHZM ZIP CSV and USDA Plant Hardiness Zone Map.