NWS Twin Cities Home Page » Historical Severe Weather Events » March 29, 1998 Tornadoes » Radar Imagery

The Southern Minnesota Tornadoes of
March 29th, 1998

Stories from the...


What Did the Storm Look Like on Radar ?

The supercell that tracked across southern Minnesota on March 29, 1998, exhibited all of the classic radar signatures commonly associated with sustained, long-tracked tornadic supercells. However, in addition to the rather spectacular “classic” signatures, there are some very interesting radar features that are evident at various points along the path of the storm, including several boundaries over extreme southeast South Dakota around the time of storm initiation, a rapid transition to supercell structure just east of Sioux Falls, cyclic mesocyclogenesis (dissipation and subsequent redevelopment of the circulation in the storm) over Nicollet County, and persistence of a very strong low level mesocyclone for over an hour after the classic reflectivity structure with the storm had decayed.

Sioux Falls Radar Loop Minneapolis Radar Loop
Sioux Falls, SD Radar Loop Minneapolis, MN Radar Loop

Here, volumetric (horizontal and vertical planes) radar data from both the Sioux Falls, South Dakota (KFSD), and Twin Cities/Chanhassen, Minnesota (KMPX) WSR-88D Doppler radars will be examined. Data will be included from 1228 PM CST (1828 UTC), which was about 30 minutes prior to storm initiation over southeast South Dakota, through 743 PM CST (0143 UTC), which was about 30 minutes after the storm had produced its last tornado in Dakota County, Minnesota, and was dissipating rapidly over west central Wisconsin. These are the data that were used in real-time on March 29, 1998, by forecasters at both the Sioux Falls and Twin Cities National Weather Service Forecast Offices to issue warnings for this storm. In all, this storm tracked almost 275 miles from development over southeast South Dakota until dissipation some 7 hours later over western Wisconsin.

 

Clear Air Returns Prior to Storm Development

0.5 degree reflectivity image from KFSD at 1241 PM CST (1841 UTC)
0.5 degree reflectivity image from KFSD at 1241 PM CST (1841 UTC)

This image shows clear air returns over southeast South Dakota approximately 25 minutes prior to convective initiation. This image, while perhaps benign in appearance to the casual observer, reveals two boundaries that appear to be quite important in the early evolution of the southern Minnesota supercell. One boundary is evident as a west-southwest – east-northeast reflectivity fine line just to the northwest of Sioux Falls.The second boundary is depicted by the rather sharp north-south oriented western edge to the low reflectivity clear-air echoes from just west of Yankton, northward to west of Parker. While it is difficult to say with exact certainty what this north-south oriented boundary is, there is some evidence to suggest that this might be the dryline sharpening up. Regardless of what the boundary is, the initial updraft for the storm that eventually becomes the southern Minnesota supercell develops along this boundary about 25 minutes after this image. While both of these boundaries are subtle, and perhaps difficult to see in a stationary image, they are quite obvious in a reflectivity loop which is shown below.

Loop of Clear Air Returns Prior to and During Storm Development

0.5 degree reflectivity loop from KFSD from 1228 PM CST through 116 PM CST (1828 UTC through 1916 UTC)
0.5 degree reflectivity loop from KFSD from 1228 PM CST through 116 PM CST (1828 UTC through 1916 UTC)

0.5 degree reflectivity loop from KFSD from 1228 PM CST through 116 PM CST (1828 UTC through 1916 UTC) showing the evolution of boundaries in southeast South Dakota just before and during convective initiation.

First Echo Southwest of Sioux Falls

4-panel reflectivity image from KFSD at 104 PM CST (1904 UTC)
4-panel reflectivity image from KFSD at 104 PM CST (1904 UTC)

4-panel reflectivity image from KFSD at 104 PM CST (1904 UTC). Lower left panel: reflectivity at the 0.5 degree elevation slice, and radar beam height approximately 3,000 feet above ground level (agl). Lower right panel: reflectivity at the 1.5 degree elevation slice, and radar beam height approximately 6,500 feet agl. Upper left panel: reflectivity at the 2.4 degree elevation slice, and radar beam height approximately 11,500 feet agl. Upper right panel: reflectivity at the 4.3 degree elevation slice, and radar beam height approximately 19,500 feet agl. The two upper panels of this image, show 20+ dbz echoes at both 11,500 feet agl and 19,000 feet agl (the small echo evident just to the northeast of Yankton, SD), and these are the first detectable radar echoes of the storm that would become the southern Minnesota supercell. Note that at this time, the radar echoes are only detectable aloft, between roughly 6,000 and 19,000 feet agl, and the lack of echo at the 0.5 degree elevation slice suggests that precipitation was likely not falling at the surface underneath the developing updraft.

Radar Echo Continues to Grow

4-panel reflectivity image from KFSD at 116 PM CST (1916 UTC)
4-panel reflectivity image from KFSD at 116 PM CST (1916 UTC)

4-panel reflectivity image from KFSD at 116 PM CST (1916 UTC), 12 minutes after that shown in Figure 3. Lower left panel: reflectivity at the 0.5 degree elevation slice, and radar beam height approximately 2,500 feet above ground level (agl). Lower right panel: reflectivity at the 1.5 degree elevation slice, and radar beam height approximately 6,000 feet agl. Upper left panel: reflectivity at the 2.4 degree elevation slice, and radar beam height approximately 9,000 feet agl. Upper right panel: reflectivity at the 6.0 degree elevation slice, and radar beam height approximately 21,000 feet agl. The radar echo has grown in both strength and depth, with a nearly 40 dbz echo evident at 9,000 feet agl, and the echo top now up to around 21,000 feet agl. In addition, 20 to 30 dbz echoes are now evident at the lowest elevation slice (the lower left panel), indicating that too much precipitation has been generated by condensation within the updraft column to be suspended aloft, and precipitation has now begun reaching the ground.

Storm Continues to Intensify

4-panel reflectivity image from KFSD at 136 PM CST (1936 UTC)
4-panel reflectivity image from KFSD at 136 PM CST (1936 UTC)

4-panel reflectivity image from KFSD at 136 PM CST (1936 UTC), 20 minutes after that shown in Figure 4. Lower left panel: reflectivity at the 0.5 degree elevation slice, and radar beam height approximately 1,600 feet above ground level (agl). Lower right panel: reflectivity at the 2.4 degree elevation slice, and radar beam height approximately 7,000 feet agl. Upper left panel: reflectivity at the 4.3 degree elevation slice, and radar beam height approximately 12,000 feet agl. Upper right panel: reflectivity at the 10 degree elevation slice, and radar beam height approximately 25,000 feet agl. The radar echo has continued to increase in strength and depth during the past 20 minutes. 50+ dbz echoes are now evident throughout the lowest 12,000 feet, and the echo top is now up to around 25,000 feet agl. The lowest elevation slice also reveals a strong gradient in reflectivity developing on the southeast side of the echo (the inflow side) which is quite common in updrafts that develop in environments with strong vertical wind shear. The echo has probably become a thunderstorm by this time, as higher reflectivities at or above the freezing level indicate that both liquid water and ice hydrometeors are probably present, which is necessary for charge separation and lightning generation within an updraft. Another weak shower has also developed to the south of the first echo, to the northeast of Yankton.

Storm Strengthens to Near-Severe Levels

4-panel reflectivity image from KFSD at 158 PM CST (1958 UTC)
4-panel reflectivity image from KFSD at 158 PM CST (1958 UTC)

4-panel reflectivity image from KFSD at 158 PM CST (1958 UTC), 22 minutes after that shown in Figure 5. Lower left panel: reflectivity at the 0.5 degree elevation slice, and radar beam height approximately 900 feet above ground level (agl). Lower right panel: reflectivity at the 2.4 degree elevation slice, and radar beam height approximately 3,300 feet agl. Upper left panel: reflectivity at the 7.5 degree elevation slice, and radar beam height approximately 12,000 feet agl. Upper right panel: reflectivity at the 14 degree elevation slice, and radar beam height approximately 21,500 feet agl. The storm has intensified further, and now exhibits several radar signatures commonly associated with severe storms. The upper left panel reveals a 68 dbz echo present at 12,000 feet agl, and a substantial three body scatter spike, or “flare” echo, which is commonly associated with hail 1 inch or larger in diameter. At this time, it is unlikely that hail that large (or perhaps any hail) is yet reaching the ground, but the very high reflectivity values and the presence of the flare echo indicate that large hail stones are growing, and being suspended aloft within the still strengthening updraft. In the lower levels (the bottom two panels), the echo has also taken on an oblong shape, with a strong reflectivity gradient on the southeast side, indicating that the storm continues to become better organized. However, the storm motion at this time remained from 220 degree at roughly 30 knots (indicating that the storm had still not deviated significantly to the right) and storm-relative velocity (Figure 6) indicates that the storm still has not developed a strong or deep mesocyclone. Thus, the storm is not yet a supercell, but appears to be slowly acquiring supercellular signatures and characteristics with time.

Velocity Data Suggests Storm is Becoming Better Organized

4-panel storm-relative velocity image from KFSD at 158 PM CST (1958 UTC)
4-panel storm-relative velocity image from KFSD at 158 PM CST (1958 UTC)

Levels are the same as the above image, except all panels depict storm-relative velocity. Although there is no strong or deep circulation present yet, there is some weak cyclonic (counter-clockwise) shear evident at all elevation slices, most notable at 12,000 feet (upper left). Considering the environment that the storm was in, and the signatures evident in Figures 6 and 7, the storm could probably be categorized as an incipient supercell at this time.

Storm Continues to Organize While Passing Over Sioux Falls

0.5 degree reflectivity (left) and base velocity (right) from KFSD at 213 PM CST (2013 UTC)
0.5 degree reflectivity (left) and base velocity (right) from KFSD at 213 PM CST (2013 UTC)

0.5 degree reflectivity (left) and basevelocity (right) from KFSD at 213 PM CST (2013 UTC). Beam height in both images is approximately 700 feet agl. The precipitation cascade from the storm is passing over the southeast sections of the Sioux Falls, SD metro area, as evidenced by the 50-55 dbz echoes. However, the main storm updraft is located just east of Interstate 29, between Tea and Harrisburg. The base velocity image on the right shows 40-45 knot inbound velocities (the bright greens) about 700 feet agl, located just to the south of the main updraft, indicating that the storm inflow continues to increase.

0.5 degree reflectivity from KMPX at 214 PM CST (2014 UTC)
0.5 degree reflectivity from KMPX at 214 PM CST (2014 UTC)

0.5 degree reflectivity from KMPX at 214 PM CST (2014 UTC). Approximate beam height is 21,000 feet agl. This reflectivity image from KMPX shows that while the storm continues to become better organized with time in the lower levels, as evidenced by the data from KFSD, the storm still remains somewhat unimpressive well aloft, as only 40-45 dbz echoes are evidence around 21,000 feet agl from KMPX at this time.

Storm Begins Rapid Intensification and Organization to a Supercell

 4-panel image from KFSD at 238 PM CST (2038 UTC)
4-panel image from KFSD at 238 PM CST (2038 UTC)

4-panel image from KFSD at 238 PM CST (2038 UTC). The two left images on both top and bottom are 0.5 degree reflectivity, the lower right image is 0.5 degree base velocity, and the upper right image is storm-relative velocity. Approximate beam height in all images is 700 feet agl. By this time the storm has moved east of Sioux Falls and is about to cross the border into Minnesota. The storm continues to become better organized in the lower levels, as evidenced by the well defined outflow in base velocity, where nearly 50 knot outbound velocities are detected (pink colors in the lower right image). However, the storm motion is now from 231 degrees at 37 knots, indicating that the storm has started to deviate to the right, and has increased in forward motion. This has a significant effect on the storm-relative inflow, which is shown in the upper right panel. When velocity is viewed in a storm-relative sense, 45-50 knot storm-relative inbound velocities are evident over much of Rock County, Minnesota, to the east of the storm, indicating that very strong convergence is occurring underneath the updraft base. Often, significant intensification of a storm occurs shortly after this type of velocity signature is evident, and this case was no exception, as seen in Figures 11, 12 and 13. This marked the beginning of a rapid transition to an intense supercell during the next 20-30 minutes over far southwest Minnesota.

Rapid Intensification

0.5 degree reflectivity from KMPX at 239 PM CST (2039 UTC)
0.5 degree reflectivity from KMPX at 239 PM CST (2039 UTC)

0.5 degree reflectivity from KMPX at 239 PM CST (2039 UTC). Beam height is approximately 21,000 feet agl. At this time KMPX was detecting 48 dbz echo at 21,000 feet, which is similar to the strength and depth of the storm for the previous hour or so.

0.5 degree reflectivity from KMPX at 245 PM CST (2045 UTC)
0.5 degree reflectivity from KMPX at 245 PM CST (2045 UTC)

0.5 degree reflectivity from KMPX at 245 PM CST (2045 UTC). Beam height is approximately 20,000 feet agl. Just 6 minutes after the time in Figure 11, the 50 dbz echo at 20,000 feet has exploded in size, with maximum reflectivity values now at 57 dbz.

1.5 degree reflectivity from KMPX at 255 PM CST (2055 UTC)
1.5 degree reflectivity from KMPX at 255 PM CST (2055 UTC)

1.5 degree reflectivity from KMPX at 255 PM CST (2055 UTC). Beam height is approximately 32,000 feet agl. Just 10 minutes later from the time in Figure 12, there is now a substantial 50 dbz echo above 32,000 feet, indicating that the storm has greatly intensified during the past 15 minutes.

Storm has Become an Intense Supercell

4-panel image from KFSD at 258 PM CST (2058 UTC)
4-panel image from KFSD at 258 PM CST (2058 UTC)

4-panel image from KFSD at 258 PM CST (2058 UTC). The two left images on both top and bottom are 0.5 degree reflectivity, the lower right image is 0.5 degree base velocity, and the upper right image is storm-relative velocity. Approximate beam height in all images is 1,500 feet agl. The storm has now acquired rather classic supercell signatures in the lower levels. A forward flank reflectivity core is evident, along with a developing appendage on the southwest edge of the echo, also known as a hook echo. In addition, tremendous convergence continues to be evident under the updraft base in both the base (lower right) and storm-relative (upper right) velocity images, with over 60 knots of radial convergence indicated. As noted in Figure 10, the storm-relative velocity image continues to indicate that the storm is inflow dominant (as indicated by the brighter blues relative to the reds in the upper right panel. The storm motion is now from 241 degrees at 38 knots, so the updraft has continued to deviate to the right, as most tornadic supercells do during their mature phase.

Impressive Supercell Radar Signatures

4-panel image from 308 PM CST (2108 UTC) from KFSD
4-panel image from 308 PM CST (2108 UTC) from KFSD

This 4-panel image from 308 PM CST (2108 UTC) from KFSD shows classic supercell radar signatures. Lower left panel: reflectivity paired with storm-relative velocity (using a storm motion of 241 degrees at 38 knots for all panels) at the 0.5 degree elevation slice, and radar beam height approximately 2,000 feet above ground level (agl). Lower right panel: reflectivity paired with storm-relative velocity at the 2.4 degree elevation slice, and radar beam height approximately 8,500 feet agl. Upper left panel: reflectivity paired with storm-relative at the 4.3 degree elevation slice, and radar beam height approximately 15,000 feet agl. Upper right panel: reflectivity paired with storm-relative velocity at the 7.5 degree elevation slice, and radar beam height approximately 25,500 feet agl. In the low levels, classic supercell reflectivity structure is now present, with a well-defined hook echo. A well-defined bounded weak echo region (BWER) is evident at 15,000 feet agl (upper left), capped by nearly 60 dbz echo at 25,000 feet. In the velocity data, a strong and deep circulation is now present at both 15,000 and 25,000 feet as well with rotational velocities of 94 knots (50 knots inbound, 44 knots outbound) at 15,000 feet and 118 knots (49 knots inbound, 69 knots outbound) at 25,000 feet agl. Finally, very strong (almost 80 knots) of cyclonic convergence is evident (near the town of Kenneth) on the 0.5 degree elevation slice, located directly underneath the strong mid level rotation. The beam height is only about 2,000 feet agl, which means that this signature is occurring near or beneath cloud base, which is very close to the ground. Strong low level cyclonic convergence beneath strong mid level rotation is often a precursor to tornado development. The storm would produce its first of many tornadoes shortly after this image, a series of weak spin-up F0 and F1 tornadoes across northern Murray County, MN between the small towns of Leota, Lismore, and Wilmont.

Numerous Elevated Supercells and Severe Storms Affect the Twin Cities

0.5 degree reflectivity image from KMPX at 325 PM CST (2125 UTC)
0.5 degree reflectivity image from KMPX at 325 PM CST (2125 UTC)

0.5 degree reflectivity image from KMPX at 325 PM CST (2125 UTC). While the supercell over southwest Minnesota rapidly increased in strength and become tornadic (the storm near Slayton in the image), numerous other elevated severe storms and supercells developed very rapidly across much of east central and south central Minnesota, from the greater Twin Cities metro area, southward to Owatonna and Albert Lea. These storms are called “elevated storms” because their updrafts are rooted in a layer of warm and unstable layer of air a few thousand feet above the ground, with relatively cool and stable air near the surface. (Note on the 2100 UTC surface map that temperatures were only in the mid 50s in the Twin Cities area, 10 to 12 degrees cooler than farther southwest along the warm front where the tornadic storm was occurring.) At least 3 supercells are evident at this time, one between Buffalo and Elk River, a second just north of downtown St. Paul, and a third between Hastings and Red Wing. Other severe storms that have at least some supercellular characteristics are located northeast of Glencoe, northwest of Buffalo, between Elk River and Center City, just south of Owatonna, and near Albert Lea. None of these storms produced tornadoes, but many of them produced hail larger than the size of golf balls.

Low Level Mesocyclone Continues to Intensify west of Fulda

4-panel reflectivity image from KFSD at 333 PM CST (2133 UTC)
4-panel reflectivity image from KFSD at 333 PM CST (2133 UTC)

4-panel reflectivity image from KFSD at 333 PM CST (2133 UTC). Lower left panel: reflectivity at the 0.5 degree elevation slice, and radar beam height approximately 3,500 feet above ground level (agl). Lower right panel: reflectivity at the 1.5 degree elevation slice, and radar beam height approximately 9,000 feet agl. Upper left panel: reflectivity at the 2.4 degree elevation slice, and radar beam height approximately 15,000 feet agl. Upper right panel: reflectivity at the 4.3 degree elevation slice, and radar beam height approximately 24,000 feet agl. The storm continues to exhibit very well-defined supercell structure in volumetric reflectivity data, with a well-defined hook echo in low levels and a BWER evident aloft. Shaun Kelly, a storm chaser from the Twin Cities area, captured video of the updraft base of the storm in this area, which showed very strong rotation at cloud base. The storm would begin producing its first of several long-tracked strong tornadoes about 15 minutes after this image.

67-Mile Tornado Path Begins

4-panel image from 348 PM CST (2148 UTC) from KSFD
4-panel image from 348 PM CST (2148 UTC) from KSFD

This 4-panel image from 348 PM CST (2148 UTC) shows how the storm looked from the KSFD WSR-88D at about the time when the tornado developed that would eventually have a path length of 67 miles and hit the town of Comfrey and the Lake Hanska area. Lower left panel: reflectivity paired with storm-relative velocity (using a storm motion of 241 degrees at 38 knots for all panels) at the 0.5 degree elevation slice, and radar beam height approximately 5,000 feet above ground level (agl). Lower right panel: reflectivity paired with storm-relative velocity at the 1.5 degree elevation slice, and radar beam height approximately 11,500 feet agl. Upper left panel: reflectivity paired with storm-relative at the 2.4 degree elevation slice, and radar beam height approximately 17,000 feet agl. Upper right panel: reflectivity paired with storm-relative velocity at the 7.5 degree elevation slice, and radar beam height approximately 24,000 feet agl. Many of the same intense supercell radar signatures are still evident, including a BWER and strong/deep circulation. Those that have some experience in looking at radar data may note that the low level “hook echo” appendage has become less well-defined from earlier times. In this particular instance, this effect is due to the fact that the storm is moving rapidly away from the radar site in Sioux Falls, and the radar is now sampling the storm at a much farther range. Features sampled by a radar at far ranges will always be less well-defined because the beam broadens with increasing distance, and the radar is sampling the storm at higher and higher levels above the ground, which is the primary reason why the storm’s hook echo now appears as more of a fat high-reflectivity appendage, rather than a well-defined sharp hook.

4-panel image from 346 PM CST (2146 UTC) from KMPX
4-panel image from 346 PM CST (2146 UTC) from KMPX

This 4-panel image from 346 PM CST (2146 UTC) shows how the storm looked at nearly the same time as in figure 18, except from the KMPX WSR-88D. Again, at about the time when the tornado developed that would eventually have a path length of 67 miles and hit the town of Comfrey and the Lake Hanska area. Lower left panel: reflectivity at the 0.5 degree elevation slice, and radar beam height approximately 10,500 feet above ground level (agl). Lower right panel: reflectivity at the 1.5 degree elevation slice, and radar beam height approximately 21,000 feet agl. Upper left panel: reflectivity at the 2.4 degree elevation slice, and radar beam height approximately 31,000 feet agl. Upper right panel: reflectivity at the 3.4 degree elevation slice, and radar beam height approximately 41,000 feet agl.

Tornado Hits Comfrey

4-panel image from 427 PM CST (2227 UTC) from KMPX
4-panel image from 427 PM CST (2227 UTC) from KMPX

This 4-panel image from 427 PM CST (2227 UTC) shows how the storm looked from KMPX at about the time when Comfrey was struck. The storm motion is now from 251 degrees at 40 knots. Lower left panel: reflectivity paired with storm-relative velocity (using a storm motion of 251 degrees at 40 knots for all panels) at the 0.5 degree elevation slice, and radar beam height approximately 6,500 feet above ground level (agl). Lower right panel: reflectivity paired with storm-relative velocity at the 1.5 degree elevation slice, and radar beam height approximately 14,000 feet agl. Upper left panel: reflectivity paired with storm-relative at the 2.4 degree elevation slice, and radar beam height approximately 21,000 feet agl. Upper right panel: reflectivity paired with storm-relative velocity at the 3.4 degree elevation slice, and radar beam height approximately 29,000 feet agl. As in Figures 18 and 19, the storm is at a fairly far range from KMPX (75 miles), and therefore the sampling is affecting how well the radar samples and resolves both the reflectivity features (low level hook, and mid level BWER), and also the circulation. Nonetheless, a very strong circulation is clearly evident with 117 knots of rotational velocity (66 knots inbound and 51 knots outbound) at the 0.5 degree slice and 122 knots of rotational velocity (85 knots inbound and 37 knots outbound) at the 1.5 degree elevation slice.

Tornado at Maximum Intensity near Lake Hanska

4-panel reflectivity image from KMPX at 442 PM CST (2242 UTC)
4-panel reflectivity image from KMPX at 442 PM CST (2242 UTC)

This 4-panel reflectivity image from KMPX at 442 PM CST (2242 UTC) shows how the storm looked at the approximate time when the 67-mile long tornado was at maximum intensity (F4 on the Fujita Scale) near Lake Hanska, between the towns of Comfrey and Hanska. The image captures of the tornado from the Roy Janni video near the town of Hanska occurred about 12 minutes after this radar image. Lower left panel: reflectivity at the 0.5 degree elevation slice, and radar beam height approximately 5,500 feet above ground level (agl). Lower right panel: reflectivity at the 1.5 degree elevation slice, and radar beam height approximately 12,000 feet agl. Upper left panel: reflectivity at the 2.4 degree elevation slice, and radar beam height approximately 18,000 feet agl. Upper right panel: reflectivity at the 3.4 degree elevation slice, and radar beam height approximately 24,000 feet agl.

First Long-Tracked Tornado Dissipates, St. Peter Tornado Develops

4-panel reflectivity image from KMPX at 513 PM CST (2313 UTC)
4-panel reflectivity image from KMPX at 513 PM CST (2313 UTC)

This 4-panel reflectivity image from KMPX at 513 PM CST (2313 UTC) shows the storm as the tornado with the 67-mile long damage path was dissipating to the west of Nicollet. However, the storm was far from finished producing tornadoes. Another long-tracked tornado was about to develop, first producing damage just east of Nicollet. This tornado would be the one to hit St. Peter. Lower left panel: reflectivity at the 0.5 degree elevation slice, and radar beam height approximately 3,500 feet above ground level (agl). Lower right panel: reflectivity at the 1.5 degree elevation slice, and radar beam height approximately 8,000 feet agl. Upper left panel: reflectivity at the 2.4 degree elevation slice, and radar beam height approximately 13,000 feet agl. Upper right panel: reflectivity at the 3.4 degree elevation slice, and radar beam height approximately 17,000 feet agl.

Tornado Hits St. Peter and Gustavus Adolphus College, Second Supercell Threatens Mankato

4-panel image from KMPX at 538 PM CST (2338 UTC)
4-panel image from KMPX at 538 PM CST (2338 UTC)

This 4-panel image from KMPX at 538 PM CST (2338 UTC) shows the storm just after the tornado struck St. Peter. Lower left panel: reflectivity paired with storm-relative velocity (using a storm motion of 251 degrees at 40 knots for all panels) at the 0.5 degree elevation slice, and radar beam height approximately 2,300 feet above ground level (agl). Lower right panel: reflectivity paired with storm-relative velocity at the 1.5 degree elevation slice, and radar beam height approximately 6,000 feet agl. Upper left panel: reflectivity paired with storm-relative at the 2.4 degree elevation slice, and radar beam height approximately 9,500 feet agl. Upper right panel: reflectivity paired with storm-relative velocity at the 3.4 degree elevation slice, and radar beam height approximately 13,000 feet agl. Notice how the low level features and hook echo are now better-resolved once again as the storm has moved much closer to the KMPX radar site (range of 35 miles to the south-southwest). The storm is also much better sampled in velocity data at this closer range, and reveals an extremely intense mesocyclone through the lowest 13,000 feet. Rotational velocities of 157 knots (77 knots outbound and 80 knots inbound) at 2,300 feet agl, 178 knots (106 knots outbound and 72 knots inbound) at 6,000 feet agl, 152 knots (67 knots outbound and 85 knots inbound) at 9,500 feet agl, and 136 knots (67 knots outbound and 85 knots inbound) at 13,000 feet agl are evident. Finally, a second supercell had developed to the west of Mankato, and there was concern for a short time that this storm might also begin producing tornadoes that could directly affect the Mankato area. However, the second storm never produced any tornadoes.

Tornado Hits Le Center

Reflectivity (left) and storm-relative velocity (right) from KMPX at 553 PM CST (2353 UTC)
Reflectivity (left) and storm-relative velocity (right) from KMPX at 553 PM CST (2353 UTC)

Reflectivity (left) and storm-relative velocity (right) from KMPX at 553 PM CST (2353 UTC). The St. Peter tornado had dissipated, but yet another one formed and hit the town of Le Center, doing considerable damage to the south and east parts of the town, including a trailer park. Approximate beam height in both left and right panels is 2,000 feet agl. Note that while the storm has begun to lose the well-defined supercell characteristics in reflectivity data, the low level circulation remains very intense.

Tornadoes Affect Montgomery/Lonsdale Area

Reflectivity (left) and storm-relative velocity (right) from KMPX at 614 PM CST (0014 UTC March 30)
Reflectivity (left) and storm-relative velocity (right) from KMPX at 614 PM CST (0014 UTC March 30)

Reflectivity (left) and storm-relative velocity (right) from KMPX at 614 PM CST (0014 UTC March 30). The Le Center tornado had dissipated, but the storm produced another tornado that affected the Montgomery/Lonsdale areas. The reflectivity structure continues to become more poorly defined with time, with the storm now having the appearance of more of a comma head, or bow echo structure. However, the circulation continues to remain very strong in the velocity data. Approximate beam height in both left and right panels is 1,500 feet agl.

Storm Crosses Interstate 35 South of Northfield Exit

Reflectivity (left) and storm-relative velocity (right) from KMPX at 624 PM CST (0024 UTC March 30)
Reflectivity (left) and storm-relative velocity (right) from KMPX at 624 PM CST (0024 UTC March 30)

Reflectivity (left) and storm-relative velocity (right) from KMPX at 624 PM CST (0024 UTC March 30) as the storm crosses Interstate 35 (the north-south red line), just north of the Northfield exit.

Storm Produces Another Tornado in Southwest Dakota County

Reflectivity (left) and storm-relative velocity (right) from KMPX at 629 PM CST (0029 UTC March 30)
Reflectivity (left) and storm-relative velocity (right) from KMPX at 629 PM CST (0029 UTC March 30)

Reflectivity (left) and storm-relative velocity (right) from KMPX at 629 PM CST (0029 UTC March 30) as the storm produces yet another tornado in southwest Dakota County. While the storm structure in reflectivity data barely resembles a supercell at all, note the very strong and tight inbound/outbound velocity couplet located just southeast of Elko (also directly south of Lakeville). This signature of 88 knots of rotational velocity (45 knots inbound and 43 knots outbound) gate to gate at 1,800 feet agl was associated with this tornado.

Storm Produces its Last Tornado in Dakota County

Reflectivity (left) and storm-relative velocity (right) from KMPX at 655 PM CST (0055 UTC March 30)
Reflectivity (left) and storm-relative velocity (right) from KMPX at 655 PM CST (0055 UTC March 30)

Reflectivity (left) and storm-relative velocity (right) from KMPX at 655 PM CST (0055 UTC March 30) as the storm produces its last tornado between Vermillion and Hastings. The tornadic circulation was associated with the cyclonic convergence signature just east of Vermillion.

Storm Dissipates Over Western Wisconsin

Reflectivity (left) and storm-relative velocity (right) from KMPX at 720 PM CST (0120 UTC March 30)
Reflectivity (left) and storm-relative velocity (right) from KMPX at 720 PM CST (0120 UTC March 30)

Reflectivity (left) and storm-relative velocity (right) from KMPX at 720 PM CST (0120 UTC March 30) showing the storm dissipating between River Falls and Ellsworth Wisconsin, after a path that crossed 3 states and nearly 275 miles, while lasting 7 hours.

Note: The write-up, radar images, and radar loops were compiled by Dan Miller, Science and Operations Officer at the National Weather Service Forecast Office in Duluth, Minnesota.


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.