Kevin Myatt

Latest entries from the Weather Journal blog

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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.

FLorida -- nailed again!

Hurricane Katrina strengthened into a hurricane late Thursday in the Atlantic east of the South Florida coast, then made landfall in Florida at mid-evening Thursday north of Miami as a Category 1 storm with 80 mph winds. It’s not an Andrew-caliber storm for that area by any means, but more than just a nuisance, with widespread wind damage to trees and power lines and, as of this writing late Thursday, at least one fatality.

It will be working its way across the Florida peninsula into the Gulf of Mexico today, where it may restrengthen for a second landfall, possibly in the Florida Panhandle on Sunday or Monday.

Katrina is the sixth hurricane to hit Florida in two years. Its projected path resembles that of Frances and Jeanne last year, except farther south and west.

We got about 10 inches of rain total out of the remnants of Frances and Jeanne last year. We’ll have to keep an eye on Katrina’s leftovers for around Tuesday or Wednesday of next week. Early call would bend the core of Katrina’s remnants to our east, but still put us where we could get considerable rain from her sometime between Monday and Wednesday, as a cold front from the west scoops Katrina’s tropical moisture northward along the Eastern Seaboard.

In the meantime, enjoy a nice weekend.

You can follow the progress of Katrina and the latest forecast maps on the National Hurricane Center link at the upper left of this page.

When a cold front isn't that cold

On Saturday, Roanoke's high temperature rose to 93 degrees.

Then, a cold front passed early Sunday. As a result, Sunday's high temperature reached only . . . 93 degrees.

Some cold front, huh?

Since that time, temperatures have backed off from the summer sizzle, and the humidity and haze have lifted as the cold front pushes grudgingly toward the Gulf of Mexico. But on Sunday, it seemed a bit misleading to call something a "cold front" that didn't make things cooler.

Actually, temperatures warming up at least some shortly after the passage of a cold front are not unusual, even if it seems illogical.

There are many reasons a cold front can really not be cold at all, at least initially:

* The core of the coolest air is well behind front. A cold front marks the leading edge of a generally cooler air mass. The front is propelled by a high pressure system, which amounts to a big mound of air — cold air in this case — that presses downward and outward. The coolest air is right under the high, and the leading edge is usually not as cool. It's usually two or three days after a front passes when the coolest air arrives. Often, a secondary front marks the passage from the initial air behind a front to the coolest air.

* Entire mass of cool air modifies. Every cool air mass moving south gradually warms, or modifies, in time as it advances into warmer latitudes. Given enough time, a cool air mass will warm enough to be barely recognizeable from the air that preceded it.

* Frontal arrival late at night or early morning clears skies. As a result, a sunny day behind the cold front is often warmer than a cloudy day in front of the cold front.

* Cold fronts usually mark the leading edge of drier air, even if the bulk of the cooler air hangs back or if the air mass has significantly modified. Drier air, besides clearing the sky in the item above, warms faster than moist air. So a sunny day in the dry air behind a front may be warmer for a few hours than a sunny day in the moist air ahead of the front would have been. Dry air, however, also loses heat faster than moist air, so nights are likely to be cooler even if the day is warm.

* Finally, unique to areas on the lee side of mountains, downsloping winds often create warmth. Winds blowing down a mountainslope dry the air out, increasing its ability to hold warmth, and also bunch the air particles together, compressing them to create heat. In our area, particularly in the Roanoke and Shenandoah Valleys and east of the Blue Ridge, the west and northwest winds brought by passing cold fronts can temporarily create a downsloping warming effect.

The much more intense version of this downslope effect, roaring off the Rockies into the Plains in winter, is called a "chinook," and can raise sub-freezing temperatures into the 50s and 60s in hours or even minutes.

If the originating air mass is exceptionally cold, the downsloping may only be able to briefly offset or slow the cooldown rather than allow a warmup. But it is common that the coldest air often settles into the Roanoke Valley when the winds have turned around to the northeast, pushing cool air down the eastern slopes of the mountains, rather than when winds are out of the northwest immediately behind a front.

On Sunday, all of these played a factor. We were at the leading edge of an air mass that was considerably modified — that's why our highs have backed into the 80s rather than the 60s and 70s like in the Great Lakes. The front arrived early in the day, allowing ample daytime solar heating in much drier air. And the west and northwest winds behind the front were heated as they blew down the Appalachian slopes.

Still, this frontal passage was a significant event on the weather landscape, a preliminary sign of the coming autumn.

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