The weather on Christmas 2016 was so unusual that it's probably a safe bet to categorize it as once in a lifetime Christmas weather for this six-county North Central Kansas area. While some past Christmases are remembered for more traditional significant winter weather such as snow, this one will go down in the record books for spring-like severe thunderstorms with damaging winds and even the first December tornado confirmed in this portion of northern Kansas since at least 1950 (when reliable records began). Then, later in the afternoon/evening, the Phillips County area endured an intense damaging wind event featuring sustained values of 30-50 MPH for a few hours and brief peak gusts around 70 MPH. These winds resulted in mainly minor damage to trees and power lines, and also flipped over several irrigation pivots. Because specific storm reports from this area were fairly sparse, the few official reports documented here likely reflect only some of the significant weather observed within North Central Kansas on this day.
Focusing more detail on the thunderstorms and tornado, the culprit was a narrow, strongly forced squall line that steadily advanced across the entire local area from west-to-east. Timing-wise, this was a fairly early show as convection first entered Rooks/Phillips counties around 11 AM and exited Jewell/Mitchell counties only a few hours later between 1:00-1:30 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 a few transient small-scale bowing segments and circulations embedded within the line, resulting in pockets of damaging winds and one confirmed, short-track tornado. This EF1-rated tornado touched down northwest of Alton around 11:45 AM and tipped over an empty bulk bin and caused very minor damage to a home.
Even though the day had already featured highly-unusual and locally-damaging Christmas weather, for parts of especially Phillips County the worst was yet to come in the form of early-evening damaging winds. While the vast majority of wind damage associated with this event focused to the north into Nebraska, automated sensors in both Phillipsburg and Logan clocked gusts of 70 MPH from the west-southwest shortly after 5 PM, followed by up to a few hours of sustained speeds to around 40 MPH before easing up. Although gusty evening winds likely brushed into adjacent local counties as well, no known reports breached High Wind Warning criteria. Forecast-wise, while fairly stout winds were anticipated to move in behind the departing low, the ferocity of peak gusts exceeded expectations.
Closing with an examination of the meteorological setup, it certainly was more reminiscent of March or April in North Central Kansas 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 north into Nebraska. Despite considerable cloud cover, temperatures rising well into the 50s F and dewpoints climbing into the upper-40s to mid-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 winds in the Phillips County area.