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Storm Surge Values from Hurricane Idalia Now Available

Hurricane Idalia made landfall at 745 am ET on Wednesday, August 30th near Keaton Beach, Florida with maximum sustained winds of 125 mph. The peak surge values observed were from Dekle Beach in Taylor County southeastward to Horseshoe Beach in Dixie County. Surge heights in this area along the immediate coast were within the range of 7 to 12 feet above normally dry ground. Read More >

Severe Weather & Flooding Event of March 3, 2012; Lowndes-Lanier Co. EF3 Tornado




A severe weather event struck north Florida and south Georgia on Saturday, March 3rd, one day after a major tornado outbreak to the north across the Ohio River Valley. Some of the thunderstorms that affected the Gulf Coast region were a continuation of the storms that had originally developed off to the northwest the day prior, although some additional storms developed early Saturday morning across the Florida Panhandle and southwest Georgia.

Figures 1 and 2. (Left) the preliminary storm reports and Storm Prediction Center morning outlook for the day prior - March 2nd. (Right) same as Figure 1, except for March 3rd.

A surface low rapidly deepened and moved northeast from southern Missouri on the morning of March 2nd, to Lake Huron northeast of Michigan on the morning of March 3rd. The low strengthened, with the pressure falling from around 996 millibars when it was over Missouri, to just below 980 millibars 24-hours later in the Great Lakes region. The intensification of the low pressure system as it ejected northeast played a big role in driving the multi-day severe weather outbreak, and even contributed to a snowstorm in Wisconsin and Michigan - with over 20 inches of snow falling in parts of northern Michigan.

Figure 3. Surface weather map analyzed at 7am EST by the Hydrometeorological Prediction Center (HPC).

In addition to the warm, moist air mass that surged well north ahead of the advancing cold front, the strong jet stream winds aloft provided another necessary ingredient for severe thunderstorms. The jet stream provided strong wind shear, or the change in speed and direction of the wind with height. Increasing wind shear tends to relate to increasing storm organization. The image below shows that the wind speeds in the middle layers of the atmosphere were even above 100 mph.

Figure 4. The position of the jet stream can be clearly seen in this image of wind speed at 500 millibars (about 18,000 feet) in the atmosphere, taken from NAM Model output for March 2, 2012 at 7pm EST. Image credit: NOAA.

As the cold front finally pushed into the eastern Gulf Coast on Saturday, March 3rd, the ingredients for severe weather shifted southward into north Florida and south Georgia - setting the stage for a few tornadoes, damaging winds, and some areas of flooding.

The Lowndes-Lanier County EF3 Tornado

The most significant damage of the severe weather event in south Georgia and north Florida was caused by a tornado that moved from just northwest of Moody Air Force Base to near Lakeland, Georgia. The damage was assessed by a survey team from the National Weather Service in Tallahassee. Most of the damage was consistent with an EF1 or EF2 tornado on the Enhanced Fujita Scale. However, the most severe damage - near Boyette Road and Highway 122 - was consistent with an EF3 rating on the Enhanced Fujita Scale. Maximum wind speeds were estimated to be around 140 mph at that location. What follows is a general description of the progression of damage, with accompanying damage survey photos. To view a static image of the damage path, click here.

The tornado likely initially developed along Cat Creek Road. We received several reports of funnels from this location while the event was ongoing, and one similar report from an eyewitness that we talked to on the damage survey. There was a house near Cat Creek Road that had uprooted trees on the property, with one or two impacting the house. Trees were generally blown down to the northeast, although a street sign was bent to the ground facing to the northwest. A few trees were also blown down along a tree line across the road. At that point, the tornado entered a more heavily forested area with no access roads. However, an aerial flyover by emergency management confirmed sporadic tree damage and a continuous damage path in that area.

Figure 5. The debris field from a destroyed mobile home along Arapaho Trail.

After the tornado cleared this forested area, the damage path began to widen and the tornado damage increased in intensity. Along Arapaho Trail, about a half mile south of Highway 122, the first instance of EF2 damage occurred as a mobile home was completely destroyed with debris blown downstream, mainly into fencing on the property. A picture of this is included above. Also in this location, a shed was completely destroyed, a camper was flipped, part of the roof of a house was removed, and a silo was destroyed with the debris found resting on the opposite side of the house from where it started. Debris from locations along Arapaho Trail were found well downstream, in some cases at least one third of a mile. Along the next cross street - Peters Road - mostly EF1 damage was observed with snapped and uprooted trees and some broken windows in houses. The survey team found a tree sitting on the ground with a root ball at the end (click link for picture), but could not locate the hole or source of the tree within at least several hundred yards. Along Peters Road gouges were observed in the ground as some debris began to impact the ground.

Figure 6. A damaged home along Bemiss Road that had exterior walls collapse. The house was also pushed slightly away from the foundation.

As the tornado crossed Bemiss Road (Highway 125) near "Walkers Crossing", the damage path began to reach its widest phase. The maximum width of the tornado was estimated to be around 390 yards or 0.22 miles based on the damage survey. Additional EF2 damage was observed on both sides of the road with wooden power poles snapped, hardwood trees snapped or uprooted, and several homes damaged. Figure 6 shows one of those homes that had exterior walls collapsed and the roof ripped away, as well as being pushed away from the original foundation. A second abandoned home was pushed six feet off the concrete foundation. Maximum winds along this part of Bemiss Road were estimated to be around 125 mph based on damage. Also near these homes, there were deep gouges in the ground, including this one that was close to 1 foot deep and 6 feet long. Large debris also continued to be found along the damage path, including these strips of metal that were twisted around damaged trees. The tornado continued east-northeast, crossing Highway 122 near Barber Road, and then impacting a property just north of 122 along Boyette Road.

Figure 7. The 0.5° radar reflectivity image from Moody AFB (VAX) around the time the tornado was at peak intensity near Boyette Road. Also around the same time, a cell phone video recorded the tornado just to the southwest.

As the tornado approached Boyette Road, it was likely reaching maximum intensity. The radar image above was taken around that time, and shows a signature known as a "debris ball". A debris ball is a "ball" of higher radar reflectivity that is caused by larger objects (debris) being lofted by a tornado. This higher reflectivity region will coincide with strong rotation near ground level, as was the case in this instance. The appearance of this signature on radar gave forecasters high confidence that a tornado was in progress, despite an actual tornado not having been reported yet. The picture of the storm at approximately the same time shows a large tornado in progress.

Figure 8. A before-and-after comparison of the EF3 damage location. The before image was taken from Google Street View. The after image was taken using a panorama app on a cell phone.

The damage at the aforementioned location was severe. A mobile home was completely destroyed with debris scattered for hundreds of yards in many directions. This site was originally unrecognizable as a mobile home to the survey team. A few trees at the location were almost totally debarked, including this one (click to see picture). A one story residence also had some roof and window damage, a small grain silo was completely destroyed, and a large shed structure was completely destroyed with debris swept well away from the original location.

Figures 9 and 10. (Left) A 7-foot section of gutter driven into the ground to a depth of 2 feet. (Right) The same gutter pulled out of the ground.

Other things were noted around this location. There were quite a few instances of objects driven into the ground, including metal bars, gutters (pictured above), branches, and other debris. There was some ground scouring noted, and many of the shrubs were ripped out of their original spots. Large debris was lofted for hundreds of yards including: what appeared to be a hatch door from the missing grain silo, a door off of a chest freezer, and a mower and propane tank. The main part of the chest freezer was found across the street. Near the location of the large shed structure that was swept away, an electric meter was ripped out of the ground, and additional deep gouges were found in the ground.

Figures 11, 12, and 13. (Left) Additional damage near the point of maximum intensity, (Middle) a mangled tractor, (Right) tree sap running down a damaged tree.

The tornado continued to the east-northeast, cutting a clear path through some dense forest in the swampland to the south of Highway 122 and to the west of Banks Lake. Around that time, the damage path began to narrow as the tornado approached the town of Lakeland. Once in Lakeland, the tornado largely caused damage to trees and vegetation, although some structures were impacted. A mobile home was completely destroyed, a nearby full shipping container was rolled about 50 feet, and some debris was driven through metal, such as this 2x4 driven into a trailer. Near the end of the tornado path it impacted the hospital in Lakeland, pushing a trailer away from its original location and damaging the ambulance station. Some antennas were also snapped at the hospital, and some damage was reported to the AC units on the roof.

Near-Storm Observations

As the strong EF3 tornado occurred around 1pm EST, it passed within a few miles of Moody Air Force Base. At the AFB, there is a reliable automated weather observation (AWOS) site that was recording weather data as the tornado passed just to the north. Thanks to the cooperation of the base weather staff at Moody AFB, Sgt. Damon Snead, and Tim Oropeza, we were able to recover the 1-minute data from the KVAD AWOS.

Below we have plotted several things in a graph. In red is the sustained wind speed in knots. The maroon dots above the red line are reported peak winds. The blue line is the mean sea level pressure in millibars. A few wind barbs were also plotted in the usual meteorological convention to show trends in wind direction. Everything is plotted against time on the x-axis (horizontally) in Zulu or UTC time. 18 UTC corresponds to 1pm EST.

The graph shows that the pressure fell steadily as the supercell thunderstorm approached, reaching a minimum at 12:57pm EST - approximately 1 minute after the tornado began just north of the Air Force Base. The pressure fell a full 1 millibar in the 10 minutes prior to that, an hourly pressure fall rate of 6 mb/hr. The falling pressure is a result of the localized low pressure within the "mesocyclone" of a rotating supercell thunderstorm. The observation at the Air Force Base just happened to be close enough to record the change in pressure.

At approximately the same time, there was a marked increase in the wind speeds as inflow to the thunderstorm and developing tornado increased. The winds backed slightly from a southwesterly direction to more of a southerly direction. Sustained winds in the inflow region of the thunderstorm peaked at 26 knots (30 mph), with gusts as high as 32 knots (37 mph). The highest sustained wind was observed at 12:56pm EST, or when the tornado was estimated to have begun.

The sharp increase in pressure around 1pm EST and a corresponding wind shift to a more westerly direction was probably due to the rear flank downdraft (RFD) on the southwest flank of the thunderstorm. With a thunderstorm that is moving to the east, the RFD would occur just to the south of the mesocyclone and tornado.