Factors contributing to record-breaking heat waves over the Great Plains during the 1930s Dust Bowl

Record-breaking summer heat waves were experienced across the contiguous
United States during the decade-long “Dust Bowl” drought in the 1930s.
Using high-quality daily temperature observations, the Dust Bowl heat wave
characteristics are assessed with metrics that describe variations in heat wave
activity and intensity. Despite the sparser station coverage in the early record,
there is robust evidence for the emergence of exceptional heat waves across
the central Great Plains, the most extreme of which were pre-conditioned
by anomalously dry springs. This is consistent with the entire 20th century
record: summer heat waves over the Great Plains develop on average ∼15-20
days earlier after anomalously dry springs, compared to summers following
wet springs. Heat waves following dry springs are also significantly longer
and hotter, indicative of the importance of land surface feedbacks in heat wave
intensification. A distinctive anomalous continental-wide circulation pattern
accompanied exceptional heat waves in the Great Plains, including those of
the Dust Bowl decade. An anomalous broad surface pressure ridge straddling
an upper level blocking anticyclone over the western United States forced
significant subsidence and adiabatic warming over the Great Plains, and triggered
anomalous southward warm advection over southern regions. This prolonged
and amplified the heat waves over the central United States, which in
turn gradually spread westwards following heat wave emergence. The results
imply that exceptional heat waves are pre-conditioned, triggered and strengthened
across the Great Plains through a combination of spring drought, upper
level continental-wide anticyclonic flow and warm advection from the north