Kevin Myatt

Latest entries from the Weather Journal blog

• Weather Journal remains on break
• Coastal low prompts Southwest Virginia flooding
• Hurricane Ida: Something extraordinary may be happening

About Kevin

Kevin Myatt grew up in Arkansas to the tune of tornado sirens and the rhythm of hailstones, aspiring to be a meteorologist before his studies and career were turned to journalism instead. Though he often chases storms, he prefers living in the cooler, more tranquil weather of the Blue Ridge. He moved to Roanoke in 1999 to take a job on the copy desk of The Roanoke Times; writing headlines and editing copy is his principal work for the newspaper today.

Each May, Kevin assists Pulaski County High School / Virginia Tech meteorology instructor Dave Carroll in leading college and high school students to the Plains to observe severe weather firsthand. The accounts of many of his storm chases can be found here on the storm chasing page of his weather blog on roanoke.com.

Kevin was an editor for "Hurricanes and the Middle Atlantic States," a book written by D.C.-area weather enthusiast Rick Schwartz and published by Blue Diamond Books that documents hurricanes striking the mid-Atlantic states since colonial times.

The Weather Journal column began in 2003 and appears on Friday's Virginia section front in The Roanoke Times. The Weather Journal blog began in 2006 and follows weather day-by-day between the larger columns.

Summer lows aren't so low anymore

I often see climatic studies that don't really seem to pertain specifically to our local area. Something may be observed generally over a large area during a long stretch of time, and be well-documented, but not be the case at all in Southwest Virginia.

However, an Associated Press article earlier this week rang an immediate bell: a clear trend nationwide toward hotter summer nights.

As if to punctuate the point, this article came in the week when at least two daily records for warmest low temperature were set in Roanoke, with a third possible on Friday if the temperature didn't fall below 74 before midnight.

According to the AP article, nearly 30 percent of the nation had "much above normal" average summertime minimum temperatures between 2001 and 2005, according to the National Climatic Data Center in Asheville, N.C.

"Much above normal" temperatures are those in the highest 10 percent on record. Typically, only about 10 percent of the nation should experience "much above normal" summer-night lows.

The trend to hotter summer nights goes back about 15 years, the article further states, with about 20 percent of the nation, on average, experiencing much-above-normal nighttime lows during that time.

"Something strange has happened in the last 10 to 15 years on the minimums," said National Climatic Data Center research meteorologist Richard Heim, according to AP. The article states that one researcher "almost fell out of my chair" when he examined U.S. night minimum temperature records over the past 96 years and saw the "skyrocketing trend of hot summer nights."

We don't have 96 years of consistent data to use in our area. The most complete and consistent records, from Roanoke Regional Airport, date only to August 1948.

But looking at record low temperatures for August from 1948 to 2000, the trend is startling.

For the 31 dates in August, the record high minimums, or warmest low temperature, for Roanoke on 10 of those dates occurred in 2000-05. The record high minimums on 17 of those dates go no further back than 1990.

If Friday's low of 76 holds up through the evening as the warmest for Aug. 4, that record combined with Thursday's low of 77 will run those numbers up to 12 since 2000 and 19 since 1990. The low of 74 on Wednesday also set a record for Aug. 2, but it replaces a record set in 2004 -- high minimum records are often being set and then reset in just the last few years.

Yes, 58 years of data aren't enough to make claims that the low temperatures are hotter than they've ever been in all of history during August, but simple mathematics shows this is an obvious aberration.

Leaving the new 2006 records out for the moment, the time period 2000-05 is six years out of 58, or a fraction more than 10 percent of that time. Yet that tenth of Roanoke's period of record accounts for about a third of the high minimum records in August.

Other categories of record temperatures do not show the same trend.

Interestingly, records for the coolest high on a given date have been more likely of late in August than records for the hottest high; there are nine low maximums, or coolest high, records in August that have occurred from 1990-2005 compared with five record highs and four record lows.

Wednesday's high of 99 is only the second record high in August since 2000.

Without going into great detail, July shows a similar pattern for high minimums, with 15 of 31 high minimum records having occurred since 1990.

Average low temperatures also suggest the trend, though not as distinctly. Three of the 10 warmest summer (June-August) average low temperatures on record in Roanoke have occurred in 2000 or later, with 2005 being the warmest at 67.25 degrees and 2002 the second warmest at 65.81 degrees. Five of the 10 warmest summer average low temperatures have occurred in 1990 or later, and all but three of the top 10 since 1987.

Average summer high temperatures do not show the same trend, with only two of the top 10 since 1990. So the nights may be getting the hotter, but the days aren't.

So I accept the hypothesis that summer low temperatures are trending significantly warmer, nationally and locally.

Why is it happening?

Global warming?

Urban heat island effects?

Natural oscillations?

All of the above?

I'm out of time and space to pick that apart today, but I'll get back to it.