Kevin Myatt

Latest entries from the Weather Journal blog

• Weather Journal taking a long break
• Yes, there's still an Atlantic tropical season going on
• Freezing temperatures likely tonight

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.

Jet stream traps cold air in Feb.

Milder weather toward the end of the month wasn't enough to keep Roanoke's average February temperature from being one of the coldest on record.

Counting back 59 years to 1948, when the weather recording station at Roanoke Regional Airport was established, February was the seventh coldest on record with an average temperature of 34.2 degrees.

It wasn't so much extreme cold -- Roanoke set no record low temperatures during the month -- but, rather, the persistence of below-normal cold days for most of the first three weeks of February. The month finished just shy of 5 degrees below normal, and was the coldest February in Roanoke since 1980.

When you put February against the background of the seven previous months, as I've done in the accompanying graphic, a remarkable pattern emerges.

Six of those eight months rank among the top 10 warmest or coolest on record, while the other two are tied for 15th warmest or coolest, putting them on the cusp of being among the warmest or coolest 25 percent.

During most of the past eight months, we've had a very amplified jet stream pattern. That's a fancy way of saying the jet stream, the fast-moving river of air 4 to 7 miles up, has been contorted into huge bulges toward the north and large dips toward the south.

When we're underneath one of the bulges toward the north, we've been warm.

When we've been inside one of the dips to the south, we've been cold. These bulges and dips have been getting stuck in place for weeks and months rather than passing through in a few days as they would in what is called a "progressive" pattern.

Think of snapping a garden hose. The harder you snap it, the larger the rises and dips that travel down the hose.

But what has been snapping the jet stream?

You have to consider El Nino a prime suspect. This up and down fluctuation of temperature has roughly coincided with the life cycle of the most recent El Nino, which rapidly declined in the second half of winter.

El Nino refers to the periodic warming of sea surface temperatures along a streak in the Pacific Ocean just north of the equator from the coast of Peru westward.

Though El Nino often gets far too much blame for a wide variety of unusual weather across the world, it does serve to give the atmosphere an additional injection of heat. This heat fuels strong storm systems in various parts of the world.

When you have strong low-pressure systems forming, they tend to pull the jet stream farther south, and also pump up warmer more stable air ahead of them that pushes the jet stream farther north. You get big rises and dips that lead to huge temperature contrasts, which in turn feed storm systems even more.

We didn't experience any of the big, wet storms this winter in our area, but certainly got in on the fluctuating temperatures.

This is a highly oversimplified explanation, but the overall idea is that adding heat to the atmosphere can increase the contrasts and extremes from point to point, rather than spreading a benign warming over a wide area.

The warm air cooks in one spot, the cold air pools in another, and as they move, a given location can experience each in turn.

There are some signals that a more placid weather pattern may be about to begin. A "zonal" pattern, with steady west to east jet stream winds and few dips or rises, may be in control for much of this month. This would mean that March would probably not be particularly warm, cold, wet or dry, but pretty average overall. May and June were our last months that were pretty close to typical.

Also, El Nino's alter ego, La Nina, a cooling of those same Pacific waters that were warm most of the past eight months, appears ready to take the stage. Unless I'm interrupted by something more urgent, we'll discuss that Saturday.