It took a while to happen, but La Niña is finally starting to make its influence known in North America.

La Niña, the cold side of the El Niño Southern Oscillation (ENSO), typically results in colder conditions across the U.S. Northern Plains and Canadian Prairies, while it remains warm across the southern tier of the U.S. Precipitation tends to favor the Pacific Northwest and the Ohio Valley while the southern tier is drier overall.

We are not really seeing that pattern developing now, however. This week is a transition week as we go out with the old weather pattern and in with the new.

Weather patterns changing

The upper-level ridge that has been stuck over western Canada and the northeast Pacific for most of January is finally making a move southeastward, getting stuck in the Southeast U.S. or just off the East Coast during the first week of February.

An upper-level trough will take its place in western Canada and cold air will pool underneath it, coming from Alaska and sometimes straight from the North Pole. This sort of upper-level setup will not be a locked-in feature throughout the entire month of February, but it should be a rather frequent sight and be the driver for weather systems throughout the month.

That cold air will leak down from western Canada and the Canadian Prairies into the Northern Plains and at times farther south and east as energy from the trough produces frequent storm systems. These tend to be bigger winter storms with a track likely farther north than we saw in January, which fell across the southern tier of the country.

The future storm track is more likely to be from Colorado or Texas into the Great Lakes or Northeast, respectively, overlapping in the Ohio Valley, which is why this area ends up with higher precipitation amounts. That could be good news for the Midwest as northern areas have seen a snow drought for much of the winter season.

Even some areas of the Northern Plains may be in the right spot during some of these storms to see increased precipitation as well. Drought in this section of the county continues to be awfully severe and any increase in precipitation would be welcomed by those in the agriculture sector worried about moisture before spring.

The cold air that pools up in western Canada and the Northern Plains is likely to push south and eastward behind these systems, giving occasional bursts of cold air. However, they are also likely to warm up ahead of the next system.

Image: The temperature forecast for the month of February is typical of La Niña with cold air in western Canada into the Northern Plains, and warm air across the south. Source: DTN

True to La Niña, the Pacific Northwest should also see an increase in precipitation, possibly coming from atmospheric river events where long streams of Pacific moisture can produce intense valley rains and mountain snows, often resulting in flooding and sometimes wind damage.

The Southwestern U.S. tends to stay drier and that is the forecast for the month of February. Drought there has been mitigated only slightly by a system this past weekend. But the drier conditions that are forecast will return the region to increasing drought conditions that could cause more issues for the region.

With the storm track and main source of energy to the north, the Southern Plains to the Southeast get waves of precipitation from the passing systems, but typically not the heaviest rainfall. Amounts tend to be below-normal. However, if the track is more frequently from Texas to the Mid-Atlantic, some of these areas can pick up heavier amounts of precipitation. The Gulf Coast is usually an area that gets only passing showers from fronts moving through.

Image: The precipitation pattern is forecast to show a typical La Niña signature with increased precipitation in the Pacific Northwest and Ohio Valley, but also across the Northern Plains while the south stays drier. Source: DTN

Long-range model simulations suggest that February may not be the only month this pattern hangs on. Though La Niña is forecast to weaken into the spring, its effects can sometimes linger for a month or two longer. DTN forecast models predict that March and April will show somewhat similar patterns, though with decreasing confidence.