The arctic shots have been very limited and brief thus far this winter. Despite a weaker polar vortex, which has a tendency to allow cold, arctic air to flow south into the United States, mild conditions have been in place for much of November and December.
A couple of arctic blasts did come in the middle-to-end of December, but lasted just a day or two instead of the typical one-to-two week stretches of frigid conditions.
Instead, the southern branch of the jet stream has remained active, quickly pushing arctic air back into Canada, and producing meaningful precipitation across the southern U.S.
This is abnormal for one reason we at DTN have been harping on for the past several months: La Nina. Typically, La Nina produces a stronger northern jet stream with a storm track across the northern tier of the country. This leaves southern areas mild but dry. This has not been the case thus far this winter.
Instead, systems have had more of a southern track, producing moderate to heavy precipitation across the Southern and Central Plains eastward, and especially across the East Coast. From the Gulf Coast to the East Coast, precipitation has been above normal.
Precipitation has been near normal in the Plains, at least maintaining soil moisture instead of getting drier, as feared under La Nina conditions. This has abated fears for winter wheat, at least in the short term.
The southern branch of the jet stream continues to be active into the new year. A system is producing widespread moderate to heavy precipitation over the Plains and into the Midwest on Dec. 29. This includes widespread snowfall of 3 to 6 inches, with locally heavier amounts, and freezing rain from Kansas to northern Illinois.
A second piece to this system will develop in eastern Texas on Dec. 31 and move northeast through the Great Lakes by Jan 2. More moderate to heavy precipitation is expected from this system as well, with snow and ice on the northern and western sides of the storm track.
Both of these pieces will likely produce above normal precipitation amounts for the last month of the year in the Southern and portions of the Central Plains, as well as some areas of the Midwest, particularly across the middle where dryness has been noted on the U.S. Drought Monitor for quite some time.
After the storm leaves this weekend, the focus turns more toward the western U.S. into next week, where large precipitation deficits have mounted through the year. Systems may still pass through the middle of the country next week, but models are producing much more muted precipitation chances than we have seen recently.
The active southern jet stream will continue to keep any significant arctic air to the north while the polar vortex continues to remain weak. The arctic air has been somewhat trapped in eastern Russia during the last two weeks. However, models hint that it may start to move into western North America toward the middle or end of next week. Should that happen, the Central and Eastern U.S. will begin to have chances for more extended periods of cold in the latter half of January.
John Baranick can be reached at firstname.lastname@example.org
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