Discussion: The most likely cause of the historic frigid air mass affecting the Midwest U.S. earlier this month and followed by sustained equally historic widespread cold affecting the West U.S. was a break in the HIGH ALTITUDE polar vortex in which the broken piece descended from the upper atmosphere (from an altitude of 15 to 30 miles) into the troposphere (where weather occurs) across Canada and toward the U.S. earlier this month.
Speculated by scientists is that this break was caused by an energy wave propelled upward through the atmosphere late last year caused by a low-level atmospheric disturbance over the much warmer than normal oceans just south of the polar ice cap.
The super cold high altitude polar vortex remains during late meteorological winter. Meanwhile as sun angle is increasing (as spring approaches) the southern portion of the northern hemisphere is warming quickly. The temperature difference between the cold polar vortex and warming tropics/subtropics is realized by an extremely fast jet stream in the middle latitudes where the highest thermal gradient between the cold and warm source regions exists.
Interestingly, and not surprisingly the set of circumstances described is related to an off-the-chart positive phase of the global atmospheric angular momentum index which peaked at +3.33 February 18th, the day of the record Norwegian Boeing 78 flight airplane speed measured at 801 mph. According to NCDC/PSD analysis the wind speeds across the East-Central U.S. and toward Pennsylvania (where the record speed occurred) was approaching 200 mph (Fig. 1) which is about 100 mph higher than normal (Fig. 2).
Fig. 1: A STUNNING wind speed analysis by NCDC/PSD identifying a near 200 mph wind speed at 250 MB (~40,000 feet) across the Missouri Valley and toward the Mid-Atlantic States propelling a Norwegian Boeing 787 to 801 mph Monday evening over Pennsylvania.
Fig. 2: The 250 MB wind speed anomalies indicate the jet stream was nearly 100 mph faster than normal on Monday across the southern Plains and Missouri Valley.
Fig. 3: The frigid high altitude polar vortex remains in-place during mid-February.