Apologies to my readers. In my haste to publish this pre-Christmas, I inadvertently omitted the all-important figures. They’ve now been included (1/2/18).
It’s time to kiss the autumnal warmth of the past few weeks across the Central U.S. goodbye, as arctic air arrives in the U.S. with a vengeance. For example, Minneapolis, MN has averaged 5.4 degrees above average through the 22nd of the month, with at least 6 days in double-digit warmth. That is slated for replacement with temperatures some fifteen to twenty degrees below average, including a forecast average of ZERO on Christmas Day.
Tulsa, OK offers similar testimony. After averaging some 6.7 degrees above average through the 23rd of this month (with 9 days in double-digit warmth), look for readings to tumble to some 5 degrees below average this coming week. After New Year’s, an even colder air mass could invade the Central U.S and even the southern Plains.
This transition is linked to a change in the upper level wind pattern from “zonal” (more west to east) flow to “high amplitude” (north and south) wind currents (Fig. 1 and Fig. 2). Notice, in Fig. 2, the formation of a “polar vortex” over Hudson Bay and a wind flow source region from north of the Arctic Circle.
© 2017 H. Michael Mogil
Originally posted 12/24/17; updated 1/2/18 (added omitted figures)
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