It’s likely to be a warm and dry winter as I reported in my previous Winter Outlook blog, and in fact over half of Texoma is now in a severe drought. And, the warm pattern persists into mid-November after the highest October average temperatures on record.
But, there’s more. The circulation pattern that we are in is known as a La Nina, and ours is expected to be one weak to possibly low-end moderate intensity. I’ve looked back at other winters where we had a weak to moderate La Nina, and found some interesting numbers. In particular, although nearly every one of these winters ran warmer than average overall, several of them had at least one severe arctic blast too.
There was a short but intense cold wave in early December 1950 while the rest of the winter was rather mild. Temperatures reached the single digits.
December 1983 was noteworthy as the coldest on record in Texoma with a two-week long severe cold wave; it was also a winter with a weak La Nina.
In December 1989 we had a much shorter cold wave, just four days; but this included a reading of minus 2 degrees in Sherman and minus 8 in Ardmore on December 23. Wow!!! That was a weak La Nina too, and the rest of the winter saw above average temperatures.
The La Nina flow has an even bigger impact on cold outbreaks farther east: Chicago had one of its coldest winters on record during the winter of 2013-2014, a weak La Nina year.
So, here’s what happens: the general steering winds during a La Nina winter are for a ridge to be in place over the western U.S. with a trough in the east (see map). This directs most of the cold outbreaks into the Great Lakes and northeast, hence Chicago’s deep freeze three years ago.
But, this flow can buckle especially during the “weak” years, and since the ridge is already in place, all it has to do is amplify and open the gates for super-cold arctic air to surge southward into Texoma. This is known as a McFarland Block.
This often happens at least once during a winter with a weak La Nina. However, other factors come into play such as the pressure patterns in Siberia and Alaska, where most of the extremely cold air comes from. Therefore, it’s not as simple as saying, “weak La Nina, therefore severe cold outbreak”, but the odds for a frigid visit are boosted in such winters.
>>> Expect a warmer and drier than average winter OVERALL
>>> An enhanced chance of at least one intense cold wave.
>>> These cold waves usually last 3 to 5 days, although it was a two-week-long cold blast in December 1983.
>>> This forecast is no guarantee of snow as it may be very cold with clear skies; there’s no way to forecast that so far in advance.
It will be an interesting season indeed.
News 12 / KXII-TV