Climate of Virginia

Weather is for today, climate is for the long-term. We use years of daily weather measurements, recorded over the decades, to define our climate. Weather changes rapidly within 24 hours. Climate changes gradually over the decades, and it requires many measurements to document if we are trending towards an ice age or global warming.

• Look at Virginia's Climate

1. the Atlantic Ocean/Gulf Stream
2. the Appalachian and Blue Ridge mountains
3. the state's complex pattern of rivers and streams

Source: Food and Agriculural Organization of the United Nations (FAO)

Virginia has a "temperate" climate. According to the climate classification system developed by Wladimir Köppen and refined by Glen Trewartha, Virginia's climate has a "mild mid-latitude" climate, and is in the subcategory of "Humid subtropical." It is coded "Cfa" on the Köppen classification system because the climate is mild, with no dry season and a hot summer. Look closely at the United Nations map showing other places where the average temperature of the coldest month <18°C and >-3°C, the average temperature of warmest month exceeds 10°C. (The green zones are places that have at least 30 mm. of precipitation in the driest month.) Think the vegetation in those places will be comparable to what you see in Virginia?

Jimmy Buffet suggests that we can change our attitude by changing our latitude. The reverse is also true - our personal comfort zone can be based on maintaining the same latitude. When the state's economic development agents encourage companies from Korea and Japan to open facilities in Virginia, they describe how the company's managers can deal with the cultural differences - and one positive factor is that Virginia has a similar climate to "home."

Virginia gets frosts and snowstorms from the cold polar air masses, especially in January. The shortest days of winter are in December, but the coldest days come weeks later in January. There's a lag time while the land of Virginia radiates heat and cools down from the summer... one reason February can be the longest month of the year. Colonists in Eastern North America were disappointed when they tried to grow crops common to Western Europe at 36° latitude. Citrus and silkworms thrived at that latitude as Western Europe, but the Virginia winters were too harsh due to the winter frosts. When Europeans reached Southern California, they found a parallel region with are a "Mediterranean" climate similar to Spain - and where orange and olive groves are successful.

What's at latitude 36° north, longitude 45° east? Source: MapQuest

We use years of measurements, recorded over the decades, to define our climate and establish "climate normals." These are based on 30-year averages. When checking statistics, be sure you don't compare apples to oranges. The 1961-1990 normals and the 1971-2000 normals are different, because the climate shifted slightly.

For example, the statistics for Abingdon show that the "Average" Maximum Temperature between 1969-2001 is not the same as the "Mean" Maximum Temperature between 1971-2000. You can't use those two numbers to say that Abindon is getting cooler and global warming isn't happening in Southwest Virginia - those statistics are not comparable, they are "apples vs. oranges." The years are not exactly the same. (Be careful with statistical jargon too. "Average" could be defined as the mean, median, or mode...)

ABINGDON 3 S, VIRGINIA (440021)
Period of Record Monthly Climate Summary
Period of Record : 12/1/1969 to 12/31/2000

NCDC 1971-2000 Monthly Normals

Tables of statistics can be dry and hard to read, while graphs to visualize them can show key points easily. A brief glance at the graphic below shows that the temperature in Abingdon rises and falls in a predictable pattern each year, while the precipitation pattern is not so clear:

The climate normals over the last 30 years will vary from the averages established by records over the last century, back to 1895 in some cases. The 30-year normals reflect just the patterns of the last 30 years. Climate can change over time, though not as rapidly as the weather. The patterns of the last 30 years may include warmer temperatures, higher moisture, etc. than the averages since 1895. Compare climate of today vs. the climate of the Pleistocene 18,000 years ago (when Pennsylvania was half-buried by ice) vs. the end of the Paleozoic 250 million years ago (when massive coal deposits formed), and the contrast will be clear.

Here is the monthly climate summary for Fredericksburg

Source: Southeast Regional Climate Center

Look closely at the average maximum temnperature in July and August. Can you guess why, in the days before air conditioning, the wealthy people from the Coastal Plain and Fall Line cities would take a vacation during the summer at the "springs," in the mountains of Virginia?

• use the Historical Climate Summaries for Virginia to compare the average winter snowfall of Back Bay National Wildlife Refuge with the average winter snowfall of Big Meadows in Shenandoah National Park (HINT: future quiz questions will require this skill...)

Mean Temperature - August
(note the location of the "hot spots" and "cool places")
Source: Southeast Regional Climate Center

• Using the Historical Climate Summaries for Virginia, look at the statistics for HOT SPRINGS and RICHMOND WSO AIRPORT. In particular, look at the Average Max. Temperature (F) for June, July, and August. Compare the heat of Richmond, a city essentially at sea level on the Fall Line, with Hot Springs in the mountains.

Don't try to memorize statistics when you can look them up easily - but be sure to use your analytical and critical thinking skills to decide when you are deciding if global warming is "proven" to your satisfaction. Analysis of the statistics is an essential part of the global warming debate, but in this class we'll just be able to touch on the basics such as:

average normal rainfall, 1971-1990

average normal minimum temperature, 1971-1990

average normal maximum temperature, 1971-1990

There's a pattern to the temperature differences in Virginia; not every place has the same weather, and not every place has the same climate. On the map below, compare the temperatures in Bath and Highland counties to Richmond and Norfolk. Need anything else to see why the rich Virginians went to the mountain springs and resorts during August, before the invention of air conditioning - and why they did not go to the mountains in the winter?

Source: SERCC, Historical Climate Summaries and Normals for the Southeast