Middle Tennessee Weather News

November 10^th Tornadoes Ravage Mid State

On Saturday evening, November 9, it became evident that severe weather was probable over middle Tennessee the next day. At 9:05 p.m. Saturday, forecasters updated the Hazardous Weather Outlook, specifying "the possibility for severe weather and isolated tornadoes across the mid state, with the peak time for severe storms between about 200 pm and 800 pm." Later that evening and into the early monring hours on Sunday, supercells that had earlier produced damage to several west Tennessee communities crossed the Tennessee River, and spawned tornadoes in Montgomery, Robertson, and Sumner Counties, killing two in Port Royal, east of Clarksville. However, the worst was yet to come.

Featured Article

One has to believe that sooner or later, middle Tennessee is going to experience a harsh winter. In the six winters since that snowy season of 1995-96, Nashville has received a combined 25.1 inches of snowfall -- an average of 4.2 inches per year. Last winter's 5.5 inches (all of which fell during February) was the most since 1995-96. (Normal yearly snowfall in Nashville is 9.1 inches.) This is not to say that all of middle Tennessee has been snowfall deficient. Several winter storms have pounded the Cumberland Plateau during the past few years. The most noteworthy event occurred on February 3-4, 1998, when Jamestown measured an unbelievable 18-inch accumulation. (This tied middle Tennessee's record for greatest single-day snowfall.)

Nor does this suggest that past winters have been lackluster. Recent Januarys have been highlighted by other types of active weather. On January 24, 1997, a rare winter severe weather outbreak resulted in 13 tornadoes across middle Tennessee -- the mid state's third largest tornado outbreak ever. Nearly two years later, on January 22, 1999, Clarksville was struck by an F3 tornado before dawn. And don't forget January 22-25, 2002, when a widespread three-day flooding event occurred across the area, with six fatalities and eleven injuries.

Still, winter is not normally known for severe weather, which is why the past several years have seemed so mild. True, the past six winter seasons (December through February) have been cumulatively warmer than normal, by an average of 2.5 degrees, but they have been slightly drier than normal as well, by an average of 0.40 inches.

So what does the winter of 2002-03 hold? According the the National Weather Service's Climate Prediction Center, the seasonal outlook for the period of December through February calls for more of the same -- slightly above normal temperatures, and slightly below normal precipitation. One can only hope.

NWS Spotlight

When the remanants of Tropical Storm Isidore moved across middle Tennessee on September 26, it marked the first time in nearly seven years the mid state had taken a direct hit from a tropical storm -- the first time since October 5, 1995, in fact, when Tropical Storm Opal brought heavy rainfall to much of the area.

Although winds associated with the storm were far less than what had been anticipated, the rainfall was not. The hardest-hit areas of middle Tennessee were those closest to the Tennessee River. Several stations reported excessive rainfall, with Waverly topping the list, having measured a remarkable 8.18 inches of rainfall during the 24 hours ending at 7:00 a.m. on Friday, September 27. Other places receiving five inches or more during the 24 hours included Tennessee Ridge (8.16), Camden (8.00), Parsons (7.71), McEwen (7.29), Big Sandy (6.75), Dover/Ft. Donelson (6.61), Montgomery (6.43), Port Royal (6.22), Clifton (5.64), Linden (5.63), Pinewood (5.29), Waynesboro (5.21), Sparta (5.20), Springfield (5.20), and Kingston Springs (5.15). For the record, Nashville measured 3.41 inches on the 26th and during the early morning hours of the 27th.

(Of note, Waverly's 8.18 inches eclipsed its record for most rainfall in one day. The previous record of 6.69 inches was established on July 6, 1967.)

Although September is one of the most active months for Atlantic tropical systems, it is historically Nashville's third driest month, behind August and October. Such was not the case this year, as most middle Tennessee stations registered precipitation totals far above normal for the month. In fact, Nashville's 6.29 inches for September was 2.70 inches above normal, and September, 2002 missed being Nashville's tenth-wettest September of record by a mere one-hundredth of an inch.

Spotter News

Following is an article published by the Amateur Radio Relay League regarding the recent tornado outbreak.

Killer Tornadoes Rally ARES Teams in Several Eastern States

NEWINGTON, CT, Nov 11, 2002--Amateur Radio Emergency Service (ARES) teams in several states have activated following an outbreak of severe weather November 10. Tennessee, Alabama and Ohio were among the states hardest hit, but the swath of violent weather and the tornadoes it spawned also affected Mississippi, Kentucky and Pennsylvania as well as parts of the Virginias. Reports from the ham radio operators involved with the ARES teams in the affected states are still coming in.

"Our weather-spotting network was instrumental in providing timely information to Nashville National Weather Service, which immensely helped their ability to issue severe weather/tornado warnings," said ARES Assistant Section Emergency Coordinator for Middle Tennessee Thomas Delker, Amateur Radio call sign K1KY.

Following the tornadoes, Delker said, Coffee County ARES was active with help from members of Rutherford County ARES. He anticipated hams would assist the American Red Cross in damage assessment and in other activities; at least one shelter was open in the county. Hams in Tennessee have been maintaining statewide emergency traffic nets.

In Ohio, ARRL Section Manager Joe Phillips, K8QOE, reported emergency nets up and running in Van Wert, Ottawa and Senaca counties, which suffered the most extensive damage in the Buckeye State. ARES organizations in Ohio District 2 and District 3 were standing by, Phillips said. Two Lucas County (Toledo) units promptly responded November 10, deploying an emergency communications trailer to Tiffin in Senaca County and an emergency communications van to Port Clinton in Ottawa County, Phillips said.

Ohio traffic nets, including the Ohio Single Side Band Net (OSSBN), were on the air. "The OSSBN will remain in session as long as it is needed," Ohio Assistant Section Manager Connie Hamilton, N8IO, told Phillips.

The Ohio Emergency Management Agency has a temporary station set up in Van Wert County on the OSSBN frequency to facilitate communication in and out of the region most devastated by the November 10 tornadoes, Phillips said.

Phillips said a tornado destroyed the home of former Ohio District 2 EC Ralph Shields, WB8YIH, in Van Wert. "Ralph reported that he was in the basement with his family when it hit," Phillips said. When family members looked up after the storm had passed, they saw that their house had been replaced by a big window to the sky.

ARES and SKYWARN volunteers also were on duty as Kentucky sustained severe storms November 10. "Twice in the same day, hams activated for severe weather," said ARRL Kentucky SEC Ron Dodson, KA4MAP. Dodson called the early morning session "minor" compared to the one that followed at 5 PM--which began with a tornado warning. "Torrential rains with hail--pea to dime-size--and winds up to 67 MPH were reported," Dodson said.

Damage in Kentucky occurred mostly in Meade and Breckenridge counties and was largely limited to downed power lines. It was a similar story in the Lexington area, where Assistant EC Pat Spencer, KD4PWL, reported hams also supplemented normal communications facilities taken out by the storm. "Apparently a major transmission line was hit on the west end of Fayette County that knocked out power to perhaps one-quarter of the city [of Lexington] and to the City of Versailles," Spencer reported.

Tis the “Flood Season”

Winter through early spring is the time of year when middle Tennessee is most susceptible to flooding. There are several reasons for the increased risk of flooding. As the upper-level wind patterns shift with the season, storm systems pass through the Tennessee Valley more often, increasing the chance for precipitation. Most of middle Tennessee averages between four and five inches of precipitation per month during November and December. Another reason for the cold season flooding is that when the growing season ends, vegetation requires less moisture from the soil and colder soil temperatures cause rainfall to “run-off” more quickly into river and stream channels. During the warm or growing season, a three-inch rainfall in twenty four hours may not produce flooding, whereas the same three-inch rainfall during the cold season could cause significant flooding.

Some middle Tennesseans may remember the Cumberland River flood of March, 1975. A storm system remained nearly stationary over the Lower Cumberland River Basin for four days. Rainfall averaged 6.7 inches over most of the basin during a sixty-hour period between March 11-14. Several stations reported storm total rainfall amounts between eight and nine inches. As a result of the persistent heavy rain, major flooding occurred along the Cumberland River. In Nashville, extensive residential and industrial flooding occurred as the Cumberland River rose to a height of 47.64 feet -- 7.64 feet above flood stage. The March, 1975 flood was one of the most severe floods on several tributaries to the Cumberland River as well. The Stones River, Harpeth River, and Red River all experienced severe flooding.

More recently, significant flooding occurred on the Duck River during January, 2002. As a result of very heavy rain, water levels rose well above flood stage at Shelbyville, Columbia, Centerville, and Hurricane Mills. Columbia experienced its worst flooding since 1991, as the river crested at 45.6 feet -- 15.6 feet above flood stage.

Why should you be concerned about flooding? Floods kill more people in the United States than any other form of severe weather. Flood waters can roll boulders the size of a car, tear out trees, destroy buildings and bridges, and pose a significant threat to human lives. While most floods cannot be prevented, there are steps you can take to protect life and property. At a minimum you should know where you are in relation to rivers and streams. Stay informed during persistent rain events by listening to NOAA Weather Radio, local television, or radio for the latest information on flood watches and warnings. And have an evacuation plan in place BEFORE flooding occurs.

Michael Murphy
Service Hydrologist

Meteorology 101

Winter is known to produce a variety of precipitation types. There's snow. There's sleet. And there's freezing rain. And sometimes we observe a "wintry mix," when two or three types of precipitation might occur simultaneously. And this doesn't even include the rare "thundersnow." So what's the difference?

Of course, we're most familiar with snow. Snow is produced when the entire atmosphere is below freezing. After forming in the mid-levels of the atmosphere, snow falls through a thick frozen layer, and usually reaches the surface intact. Sometimes, a thin, surface-based layer of above freezing temperatures may exist, allowing for some melting. But even with a surface temperature of 33 or 34 degrees, "wet snow" is still snow.

Then things start to get a little more complicated. Consider sleet (technical name: ice pellets). Sleet begins as frozen precipition at some height above the surface. This precipitation then descends through a relatively thick "warm" layer, where it melts into rain. The rain then re-enters a sub-freezing layer as it approaches the surface, where the droplets re-freeze into ice pellets before striking (although not necessarily sticking to) the surface.

Perhaps the most hazardous of all precipitation types is freezing rain. Similar to sleet, this type begins its life-cycle in a sub-freezing layer, and at some point falls through a near-surface "warm" layer, where it melts into rain. Unlike sleet, though, the rain enters a shallow sub-freezing layer -- too shallow to re-freeze the rain before reaching the surface. Here's the catch. In order for freezing rain to occur, the surface must be 32 degrees or colder, so that when this rain strikes a surface, such as a road, or a car, or a power line, the rain freezes on contact, thereby bonding to whatever surface it has struck. The classic ice storm, characterized by impossible driving conditions, broken power lines, and sagging tree branches, is caused by freezing rain.

So as you can see, winter forecasting can often be challenging. A forecast that's off by only one or two degrees can mean the difference between rain, snow, sleet, or freezing rain, or a mixture of two or more of these precipitation types. A forecast of 33 degrees and sleet could turn out completely different if its 31 degrees with freezing rain, or 35 degrees and just rain. Forecast precision is most critical during these times, for a temperature forecast that's off only slightly can still be responsible for sending out salt trucks when they were not needed, or sending school buses on their routes when they should have stayed at home. Then the forecaster is left pulling out his hair between the invariable queries of how and why.

More News Items

NOAA Weather Radio transmitters are being installed at Hickman (between Carthage and Smithville), and also at Winchester. They are to be shipped between December 2 and December 9, and should be running by Christmas. Other new sites, Cypress Inn (Wayne County), Russell Hill (Macon County), and Spencer (White County) are set for 2003. Lincoln County is pursuing a federal grant for a Fayetteville area NOAA Weather Radio.

Photograph of the Quarter

The honoree this issue is storm spotter Greg Bearden, from Spring Hill. This photograph was taken in northeast Maury County on October 3, at approximately 6:30 a.m., when Tropical Storm Lili was entering the area. The view is toward the eastern sunrise. Lili, of course, became the second tropical storm to strike the middle Tennessee during an eight day period, following Isidore's strike on September 26.

Mr. Bearden had earlier sent us another worthy candidate. This gem, a photograph of a towering cumulus cloud, was snapped on August 23 in eastern Maury County.

Finally, Sharon Prince of Franklin County sent us our second "honorable mention." Sharon describes her photograph as a "dramatic presention of mountain mists." This picture was taken on Sunday, November 3, during the afternoon, following a series of rainy spells. Ms. Prince explained that such phenomena provide the run-off that drains into Bean's Creek from the west side of Keith Springs Mountain, which is south of Huntland (extreme southwest Franklin County).