Reporting Jeff Jamison
Filed underStorm Team Blog
It is tempting to think that after going 2/3 of the way through Winter without a major Arctic outbreak or ice storm that we can slide through the last 1/3 without any cares. But I would caution that thinking. February, afterall, has been a pretty rough month for North Texas during the past couple of years for sure. The long-wave weather patterns and other atmospheric-oceanic oscillations that we keep tabs on are still indicating that we’re just one good cold front away from a major weather change in North Texas.
Let’s start with the most well-known weather influence – La Nina. It is still present in the Pacific…the relative cooling of the waters in the eastern Pacific that tend to drive the jet stream farther north during the winter months. This keeps the southern United States generally milder and drier. La Nina is forecast to continue through February and into Spring.
We’ve talked about the Madden-Julian Oscillation before. It is a cycle that develops over the southern Pacific and Indian oceans that can tend to overwhelm the La Nina effects and bring the southern U.S. more moisture when the MJO is in an active phase. The MJO was very active in December, which lead to many bouts with clouds and rain here in North Texas. It hasn’t been nearly as active in January, which lead to more sunny days than not. Of course, even with less rain events, the two storms we had during the month of January gave us over 6″ of rainfall!! The Madden-Julian Oscillation is getting active again, which leads me to believe we could see more frequent chances for storm systems to track farther south across our part of the country.
The other parts of all this are the Arctic Oscillation and the North Atlantic Oscillation. These indexes give us a better clue whether or not brutal Arctic air bottled up over Siberia, Alaska and northern Canada has a chance of spilling south into the U.S.
Whenever the AO and NAO are in positive territory, there is less of a chance for cold air to make it very far south. Now the AO has been negative since mid-January, but the actual jet stream has thus far remained too far north to bring that cold air south into Texas. Tempeatures have been running below 40° below zero or lower in much of central and northern Alaska. But until we get a “blocking pattern” in the upper levels, where high pressure builds over Alaska and begins to dislodge the cold air and send it south, the really cold air will stay put.
The NAO plays a similar role…when it is positive, the cold air tends to stay bottled up in Canada. We’ve been in a negative NAO for awhile, but forecasts take it back to positive mode in the next few days. Both the AO and NAO are difficult to forecast more that a couple weeks out.
However with the AO showing a negative bias for the first half of February, the record-setting cold in Alaska, and a more active MJO, the potential is still very real for an Arctic cold front to blow through North Texas and/or a wintry precipitation event to occur in February.
But I generally believe that La Nina will still be felt in February with a lot more mild days than really cold days….but we’ll be watching that super cold air in Alaska to see if there’s a chance it pays us a visit later this winter.