27 May 2024, Memorial Day

Pittsburghers used to have a tradition that Memorial Day was the start of outdoor tomato planting season. But if you grow tomatoes today you know that’s not the case. You probably planted them weeks ago.

Just 50 years ago Pittsburgh had an annual average minimum temperature of -10 to 0 degrees F and those numbers didn’t change ten years after this USDA map was produced in 1960.

But the climate is changing rapidly now. Last year USDA officially revised their Hardiness Zones as shown on the 2023 map below.

The Pittsburgh area shifted a 1/2 zone warmer in eleven years. Notice the paler color in the river valleys in Allegheny County on the zoomed map below. Our average annual lowest temperature used to be -5° to 0°F but it jogged 5 degrees warmer. Now it’s 0° to 5° F.

None of this is a surprise. We were certainly felt hot in April, the warmest on record.