Thunderstorm Wind — Dawson, Nebraska

2019-08-11 · near Cozad, Dawson, Nebraska

Event narrative

An 81 MPH wind gust was measured by a mesonet station located 1 mile north-northeast of Cozad. Emergency management reported tree damage and downed power lines in the area, along with overturned pivots. One of the more notable damage scenes involved Cozad High School, where a large portion of the roof was ripped off of the library, allowing rain water to pour in. This damaged thousands of books, along with shelving and some electronics. Nearby, a metal storage building was destroyed, parts of it lofted into a nearby home and piercing a hole in its roof.

Wider weather episode

The late evening of Sunday the 11th into the early morning of Monday the 12th featured a rather perplexing thunderstorm complex within South Central Nebraska, as what appeared to be a favorable setup for potentially widespread damaging winds ended up yielding only one localized (albeit significant) area of known damage. That one area was in and near Cozad in Dawson County, where an intense storm struck around midnight CDT, prompting an unofficial 81 MPH wind gust on a personal weather station. In addition to numerous downed tree limbs and power lines across town, some of the most notable damage occurred at Cozad High School, where a large portion of the library roof was ripped off. This allowed rain water to pour in, damaging thousands of books along with some shelving and electronics. Also in town, a metal storage building was destroyed, parts of it lofted into a nearby home and piercing a hole in its roof. However, despite what occurred in Cozad, the vast majority of South Central Nebraska only experienced sub-severe wind gusts in the 40-55 MPH range. The underachieving nature of this severe storm event was rather surprising (albeit fortunate), especially considering that 21 local counties were placed under a somewhat-rare Particularly Dangerous Situation (PDS) Severe Thunderstorm Watch.

Breaking down timing and storm evolution, the leading edges of what initially appeared to be an intense linear mesoscale convective system (MCS) with a bow echo radar signature entered southwestern local counties between 10:30 p.m. and midnight CDT. Over the next few hours, the main corridor of weaker-than-anticipated outflow winds traversed primarily counties south of Interstate 80 before exiting into southeast Nebraska around 2 a.m. CDT. Meanwhile, the isolated severe storm in Dawson County occurred north of the where the most intense winds would typically be expected, possibly tied to brief intensification associated with a mesoscale convective vortex (MCV). To be sure, the broad mesoscale environment appeared quite supportive of potentially-widespread severe storms, featuring 1000-3000 J/kg mixed-layer CAPE and around 40 knots of deep-layer wind shear. This high instability was fueled by a very humid airmass with surface dewpoints into the low-mid 70s F. In the bigger picture of the mid-upper levels, broad west-southwesterly flow was the story, as an embedded shortwave trough kicked off the initial storms of the afternoon and evening over the High Plains of Colorado/Wyoming/western Nebraska. At the surface, South Central Nebraska resided slightly north of a weak, west-east frontal zone centered across northern Kansas.

View location on OpenStreetMap → (40.8834, -99.9627)

Source: NOAA Storm Events Database, event_id 849139. Narrative written by the NWS forecast office that issued the report.