  Over the last eight years, a rich dataset of mid-infrared CH4 observations
from the TEXES instrument at IRTF has been used to characterize the thermal
evolution of Jupiter's stratosphere. These data were used to produce
vertically-resolved temperature maps between latitudes of 50{\deg}S and
50{\deg}N, allowing us to track approximately two periods of Jupiter's
quasi-quadrennial oscillation (QQO). During the first five years of
observations, the QQO has a smooth sinusoidal pattern with a period of
4.0$\pm$0.2 years and an amplitude of 7$\pm$1 K at 13.5 mbar (our region of
maximum sensitivity). In 2017, we note an abrupt change to this pattern, with
the phase being shifted backwards by ~1 year. Searching for possible causes of
this QQO delay, we investigated the TEXES zonally-resolved temperature
retrievals and found that in May/June 2017, there was an unusually warm thermal
anomaly located at a latitude of 28{\deg}N and a pressure of 1.2 mbar, moving
westward with a velocity of 19$\pm$4 m/s. We suggest that there may be a link
between these two events.
