| "Climate is what you expect; weather is what you get" is the old saying describing the long-term (climate) vs. the short-term (weather). You only need to look outside the window if you want to see the current weather - but it takes a little more study to understand the climate of a place in Virginia... |
Climate is assessed in cycles of 30 years. That timeframe is not very helpful if you need to decide what clothes to wear tomorrow, but essential if you have to evaluate the risks of floods damaging property in a river's floodplain before you approve a 30-year mortgage.
Weather varies by distance, as well as by time. When it rains in Roanoke, the sun might be shining in Chincoteague.
When Hurricane Floyd dumped 17 inches of rain on Williamsburg on September 16, 1999, the city of Roanoke got 1 inch. The City of Roanoke kept its water restrictions in place, since Carvin's Cove reservoir was still 25 feet below the spillway. And on a local scale, storms that bypassed the reservoir for Roanoke City were kinder to Roanoke County in 1999. The Spring Hollow Reservoir near Salem, just a few miles away from the city reservoir, received enough runoff from its watershed to supply sufficient water all summer for county residents.
So obviously storms pay no attention to political boundaries. Still, because it's administratively convenient for humans, we divide Virginia into 6 distinct climate divisions.
Virginia has a Goldilocks climate - "not too hot; not too cold," just like the porridge in the old fairy tale. In climate textbooks, Virginia has a temperate climate like many other areas, including England and Korea.
Virginia has a "humid, sub-tropical" climate. The sub-tropical part is easy to understand - because we get frosts, we're not tropical. However, if you've ever been in Virginia through a summer, you know it's not the heat, it's the humidity that makes the summers "sticky." More than anything else, that's what people in Tidewater notice most about Virginia's climate. Of course, in Tidewater you're near water all the time - the Potomac/Rappahannock/York/James rivers and their tributaries, the Chesapeake Bay itself, and the Atlantic Ocean if you live on the Eastern Shore or Virginia Beach.
There is a significant difference in the relative humidity in Richmond in April compared to August. Before air conditioning appeared in the 1930's and then became common after World War II, the best way for Virginians to escape the heat was to retreat to mountain resorts. Highland County's name reflects its elevation. Moist air drops in temperature 3.3 degrees Fahrenheit, for every 1000 feet you climb in elevation (the adiabatic lapse rate). So if you climb 3,000 feet in elevation, on the average the air will be 10 degrees cooler. And because the cooler air holds less moisture, your body can cool off easier through evaporation. Ever hear folks in Arizona say "hey, it doesn't feel like 100 degrees -it's so dry out here..."? You can get the same cooling effect in the mountains of Virginia... though the lower humidity in Arizona is often more pronounced.
That's one reason Blacksburg is attracting retirees, including folks who moved from the Snow Belt to Florida but wanted to return to a place with seasons. They may not want to return all the way home to harsh winters, however, so they choose to settle in an area that's both north of Florida and higher in elevation. Those who settle in places like Bristol (Tennessee and Virginia) and Asheville (North Carolina) and Roanoke are known as "halfbacks." These are the retirees who made it only halfway back to their old home...
Virginia is not always warm, as shown by this record from Thomas Jefferson's Garden Book, 17741:
Vegetation is an excellent clue to the climate of an area - think of forests as "climate you can touch." Whatever the weather may be on a particular day when you visit a community, the long-term climate can be seen in the plants. If you fly from Dulles to Los Angeles in January, after you land you can smell jasmine in bloom and see strawberries being harvested - while watching the Weather Channel describe "liberal leave policy" in Washington due to freezing rain and snow. If you happen to visit Los Angeles again in June, the weather then may be similar to Dulles... but one look at the vegetation away from the airport, and you can be confident the climate in those locations is substantially different.
The Mediterranean climate of California lacks the frosts of Virginia, so different species thrive there. Look in the backdrops of TV shows that supposedly are filmed in the Washington, DC area and you might see chaparral, live oak, or eucalyptus trees. You won't find those species in Arlington County... so you know the producers taped the scenes at Southern California locations.
The primary agricultural area of Virginia, Augusta and Rockbridge counties in the Shenandoah Valley, have a growing season of roughly 160 days. In other places, the average growing in Virginia season as long as 200 days. Obviously it's not the length of growing season, but factors like the soil from the limestone bedrock, the type of crops being grown, and even the dedication of the farmers that make the Shenandoah Valley the prime agricultural area of Virginia.
The plant hardiness zone map shows the influence of the Blue Ridge - the pink area east to the east is mapped as zone 7a with an average minimum temperature of 0-5 degrees Fahrenheit, while the area to the west is zone 7b with an average annual minimum temperature 5 degrees cooler. And in the Tidewater you can see the ifluence of the Chesapeake Bay and Atlantic Ocean, keeping average annual minimum temperatures 5 degrees warmer than the Piedmont and 10 degrees warmer than the Valley and Ridge provinces. The vegetation reflects, in part, its "cold hardiness ratings" - the ability to withstand the cold.
