Thunderstorm Wind — Buffalo, Nebraska

2016-12-25 · near Kearney, Buffalo, Nebraska

Event narrative

Wind gusts estimated to up to 80 MPH caused damage in the Kearney area. Around 10 pine trees were blown down, as were a few irrigation pivots. Construction trailers were blown over near Kearney High School and a barn lean-to was damaged on 46th Avenue.

Wider weather episode

The weather on Christmas 2016 was so significant and unusual that it's probably a safe bet to categorize it as once in a lifetime Christmas weather for this 24-county South Central Nebraska area. While past Christmases (such as 2009) are remembered for more traditional significant winter weather such as heavy snow/blizzards, this one will go down in the record books for spring-like severe thunderstorms with damaging winds and the first three December tornadoes in Nebraska since 1975, followed by an intense damaging wind event during the evening hours featuring sustained values of 30-50 MPH and peak gusts generally 55-75 MPH. All things considered, the evening high winds were actually more impactful to the area as a whole than the daytime thunderstorms, given that fierce speeds persisted as long as two to three hours in most locations. These winds resulted in widespread, mainly minor damage to trees, power lines (promoting several power outages) and some structures, and also flipped over numerous irrigation pivots. In reality, the official convective and non-convective storm/damage reports documented here only capture a portion of all significant weather/damages observed within South Central Nebraska.

Focusing more detail on the thunderstorms and tornadoes, the culprit was a narrow, strongly forced squall line that steadily advanced across the entire local area from west-southwest to east-northeast. Timing-wise, this was a fairly early show as convection first entered far southwestern local counties such as Furnas/Gosper between 10:30-11:30 AM, swept through central areas including the Tri Cities between 12 PM and 1:30 PM and eventually exited far northeastern counties such as Polk/Nance between 2-3 PM. While most locations experienced sub-severe winds up to around 50 MPH, brief heavy rain and perhaps small hail with the passage of these storms, there were several transient small-scale bowing segments and circulations embedded within the line, resulting in pockets of damaging winds and three confirmed, short-track tornadoes. These tornadoes (two rated EF-0, one EF-1) all occurred between 11:45 AM-12:30 PM and lasted only a few minutes. The first tornado, near Funk, destroyed several large power poles. The second tornado produced minor damage at a farm southeast of Minden, and the third destroyed an outbuilding at Blue Sky Estates northwest of Gibbon. A few of the most significant damage reports not directly attributed to tornadic circulations included: construction trailers blown over and a barn destroyed on the west side of Kearney; and machine shed and tree damage southeast of Bruning.

Even though the day had already featured highly-unusual and locally-damaging Christmas weather, for many places the worst was yet to come in the form of the widespread evening damaging wind event, which largely unfolded under clear skies due to strong subsidence on the backside of an intense low pressure system. At nearly any given affected location, there were at least a few peak gusts of 60-75 MPH from the west-southwest, along with two to perhaps three hours of sustained speeds 30-50 MPH. Timing-wise, high winds rapidly overspread most of South Central Nebraska from southwest-to-northeast, with severe-criteria gusts first measured in counties such as Furnas/Harlan shortly after 5 PM, central locations such as Grand Island/Hastings between 6-7 PM and far northern counties such as Valley by 8 PM. Finally, between 9:30 and 10:30 PM, winds eased below High Wind Warning criteria for the night. Based on dozens of reports from automated sensors, only the southeastern fringe of South Central Nebraska (generally southeast of a Red Cloud-Geneva line) was spared widespread damaging winds. Meanwhile, across the rest of the area, just a sampling of peak measured wind gusts included: 76 MPH at Aurora airport, 75 MPH at Grand Island airport and near Oxford, 73 MPH near Franklin, 72 MPH in Osceola and 71 MPH at the NWS office in Hastings. Needless to say, these evening winds resulted in fairly widespread, mainly minor damage to trees, power lines and some structures, and also flipped over numerous irrigation pivots. Forecast-wise, while gusty winds were anticipated to move in behind the departing low, the ferocity of this event exceeded expectations.

Closing with an examination of the meteorological setup, it certainly was more reminiscent of March or April in South Central Nebraska than late-December. In the mid-upper levels, a powerful, negatively-tilted vorticity maximum deepened over the course of the day as it emerged from the Central Rockies, reaching north central Nebraska by early evening. Just to the southeast of the mid-level low center, a formidable upper jet streak of 120+ knots migrated overhead. At the surface, it was a classic setup for low-topped, severe convection as a deep low pressure system intensified to around 986 millibars in far northeast CO by noon, allowing a warm front to surge northward across South Central Nebraska. Despite considerable cloud cover, temperatures rising into the 50s F and dewpoints climbing into the mid-40s to low-50s F allowed mixed-layer CAPE to reach a few hundred J/kg. Combined with strong deep-layer wind shear of generally 60-80 knots and exceptional low-level shear of 50-60 knots, even this relatively meager instability proved sufficient for damaging winds and brief tornadoes. By early evening, the intense surface low pressure center reached north central Nebraska, placing the local area behind an occluded Pacific cold front and within a zone of deep atmospheric subsidence. In tandem with other factors such as steadily-rising pressures and increased vertical mixing, this allowed very strong west-southwest winds within a few thousand feet of the surface to mix downward, driving the evening damaging wind event.

View location on OpenStreetMap → (40.7000, -99.0800)

Source: NOAA Storm Events Database, event_id 670373. Narrative written by the NWS forecast office that issued the report.