Source: Analysis of historical weather data from NOAA.
Stealth frost
It looks like we’re going to have a few nights with freezing temperatures this week, here in Vienna, VA.
I’ve been doing a few chores in and around the garden to get ready for that. The most important of which was moving a large potted lime tree into the garage. Even a touch of frost and that would likely die back to the ground. I’ve also drained all the water barrels, and I’m bringing hose timers and other frost-sensitive objects inside.
This means it’s also time to redo my prior analysis of trends in first frost. It’s been unseasonably warm in the East, so it would be no surprise if this year’s first frost were a bit later than usual.
But when I actually looked at the data, I got a surprise: Dulles Airport (my standard for this frost analysis) recorded a frost about three weeks ago, on October 21. I missed that, and clearly we didn’t get a frost in Vienna, based on (e.g.) the fact that my okra plants are still alive.
That said, on average, first frost in my area is now about 20 days later than it was in the 1960s. As you can probably see from the graph, virtually all that change has been in this century. That couple-of-weeks shift in the first frost date appears to be a fairly widespread phenomenon (per this reference).
That’s consistent with the continued northward shift of the USDA hardiness zones. They update those every so often, using more recent historical weather (i.e.) climate data. With the most recent up date (2012, using the 30 years of weather ending 2010), most of the zone boundaries slid north, compared to the prior map (using the 30 years ending in 1990). Apparently, the average rate of travel of the hardiness zone boundaries is reported at 13 miles (north) per decade (per that same reference). That varies widely, as zone boundaries at the coast shift more slowly, due to the moderating effects of ocean temperatures.
In any case, it will be sometime around 2040 before Vienna, VA makes it into Zone 8 — or Zone 8 makes it to Vienna — take your pick.
Source: NOAA, via the New York Times
So I guess it’s still a bit early to expect climate change to save me from these frost-related chores. But give it enough time, and we our descendants our descendants, if any, will have no problem growing palm trees around here.
As was true at last year’s first frost date (Post G21-057), indoor relative humidity remains high. That said, I’m keeping an eye on it, and when it drops below 40%, I’ll start running my humidifiers. I summarized why that’s important for prevention of respiratory infections in Post #894.
Source: American Society of Heating, Refrigerating and Air-Conditioning Engineers
