This past Christmas Day resulted in interesting weather across the central Plains. From strong thunderstorms in Kansas to the blizzard conditions in the Dakotas, the stockings were full of interesting weather Christmas morning. Nearly the entire state of Kansas, excluding the extreme western parts of the state, were impacted by a low-end squall line.
I spent the holiday weekend in northern Kansas and on Sunday, December 25th, it shaped up to be an active weather day across Kansas (albeit low end). Regardless, thunderstorms lit up on Doppler radar like a Christmas tree in western Kansas early Sunday morning, and progressed across the entire state of Kansas throughout the day.
Notice on the base reflectivity image that there were several lightning strikes being detected on the radar imagery. There was a stronger axis of thermal instability (CAPE) in the western portions of the state near 600-800 J/kg, as sampled on the observed morning sounding from the National Weather Service in Dodge City, Kansas. This line of storms had cloud tops around 30-35,000ft, as overall thermal instability was lacking further east. Eventually, cloud tops were no longer high enough to generate lightning and the storms continued east as a low-topped convective line.
We positioned in Courtland, Kansas, about one mile north of town and watched the squall line approach. It was not severe warned (severe thunderstorm warning criteria is winds in excess of 50 knots; equivalent to 58mph, and quarter sized hail), but it did put on an impressive show as the gust front moved toward us. The rain curtains bowed out as we estimated sub-severe gusts of 40-50mph that surged out of the downdraft, and a few areas of heavier rain were noticed as that is where downbursts were occurring as well.
Continuing further east of Courtland we drove out of the core of the squall line since it moved over us, and then traveled southward on Highway 81. As we traveled south on Highway 81 towards Bennington and Salina, Kansas, the squall line crossed over us again. However, the gust front moved further ahead from the precipitation as the forward propagation of the line increased. As a result, we were able to get a clear visual of the sinking motion behind the gust front (this is where the winds aloft mix down to the surface, and where the strongest winds occur within a squall line). This region of the squall, in slang terms, is known as the “whale’s mouth”. The term was coined due to the backside of a gust front looking like the inside of a whale’s mouth.
Being underneath the leading edge of the gust front unveiled some luminous colors, including some mixture of light green and blue which was indicative of hail aloft. However, the hail was small due to the lack of strength in the updrafts and low cloud tops. The line of storms continued east across the eastern portions of Kansas and gradually weakened into gusty showers, as it entered an environment that was unfavorable for thunderstorm maintenance.[Updated 3:54pm CST, 12/29, to add other confirmed tornadoes to the list]
There were; however, five tornadoes that were confirmed across southwestern Kansas over the next several days by the National Weather Service field office in Dodge City, Kansas, and Hastings, Nebraska, respectively (note that the NWS Hastings county warning area covers a part of north-central Kansas). Some of the tornado reports came from the public at the time of occurrence, as there was minor damage reported in some areas across southwestern Kansas and southern Nebraska.
All of the confirmed tornadoes in Kansas thus far have been rated EF-0, with winds between 70-85mph determined by both National Weather Service field offices mentioned above. An EF-1 tornado with estimated 100mph winds was confirmed in southern Nebraska by the National Weather Service in Hastings as well. More information will be added when surveys are complete for a possible sixth tornado that occurred in Rush County, Kansas, on Christmas Day.
Video of the squall line as it approached Courtland, Kansas, can be seen below. You will notice the rain curtains bow out. That is evidence of strong downbursts along the leading edge of the gust front, and can be seen in almost all squall lines (which is dependent on the orientation of the squall line). Damage did occur within the vicinity of Courtland from the gust front, as a few outbuildings and sheds were destroyed via images on Twitter.