WEATHER OUTLOOK

Fall, Winter and Spring Outlook Hinges Upon Another La Niña

By Matt Makens, Atmospheric Scientist

La Niña will spread its impact across the country for the second year in a row leaving the West in dire need of water. Ocean conditions point toward continued drought for the western U.S. as another La Niña event is expected this fall, winter and spring.

La Niña, and its counterpart El Niño, get a lot of attention this time of the year, and for a good reason. Both create recognizable weather patterns across the globe. drought as well as sharply cold conditions during the winter for the central U.S.

Although last year will be looked at, I believe 2013 and 2017 are stronger candidates as similar years to what we should expect this go-round.

These analogous years show similar ocean and atmosphere conditions, and therefore, are the historical basis for which to build this outlook. In this case, the combination of the most similar years yielded the following results for wet (green) and dry (orange) areas from September through May.

Temperatures took on the following combined look of those analogous years with cooler than average areas in blue and warmer areas in red.

The fall through spring 2021-2022 forecast will jog your memory on La Niña years of the past, most recently last year, which recorded a rapid intensification of the western and northern U.S.

I am not trying to imply that all La Niña or El Niño years will produce the same result for your area; however, there are distinct trends that we will look at now.

Part of the recent trend is to note ocean conditions elsewhere that will, in this case, work toward reinforcing La Niña’s grip on the West.

Cool water is observed southwest of California and warm water in the northern Pacific near Alaska, which both lead to reinforcing drier-than-average conditions across the West. This effectively limits the needed moisture for the Pacific Northwest to the Desert Southwest.

Some factors will need to be watched closely over the next several months, mainly that goes to watching when this La Niña fades, and El Niño develops. As of this writing, that is most likely for later 2022, but an earlier onset would be an ideal scenario for providing water to the drought-stricken West.

As it stands now, La Niña will control us through early and mid-2022, which is a lousy situation for water in the West. The first-ever federally declared water shortage was issued in August for those utilizing the Colorado River, and recommended conservations/restrictions are certainly prudent considering this outlook. Now to the outlook for September 2021 through May 2022: Northwest: The northeastern parts of the region will fare better for water than for those elsewhere. That part of the Northern Rocky Mountains may see an uptick in snowfall in the winter and spring. Wetness here is more frequent than dryness in similar years. Much of Idaho’s lower country as well as Oregon and Washington will more frequently end the run being drier-than-average. Fall (September through November) is more frequently drier-thanaverage, as is early to mid-winter. Late winter through spring will see an increase in moisture. Of the three seasons, spring has a higher probability of moisture versus fall and winter. In total, this entire region is 30 percent likely to be wetter-than-average for this period. There is some model data to indicate that the Pacific Northwest will be wet throughout the period. That same modeling suggested the same wetness for last year, which didn’t pan out, and should not be counted on as a reliable data input at this time. Temperatures are likely to be near to warmer-than-average.

West: These states have a 10 percent probability of ending this period wetter-than-average. The ocean situation near-to and farfrom this region is too powerful a drought signal to hope for much moisture. Improvement can come when, and if, El Niño establishes itself, but that will be well into 2022. Plan on another bad year Northern Rockies: Montana and northwestern Wyoming will likely fare the best in terms of moisture for this region. Overall, for the period, this region has a 60 percent likelihood of wetter-thanaverage conditions. The driest areas are historically eastern South and North Dakota, which will lead to further drought conditions here. Although somewhat evenly split between the seasons, the spring is likely to be the best opportunity for moisture. Model projections are less optimistic about moisture for this region and keep this area in an equal chance for above or below average moisture. Temperatures east of the mountains will be cooler-thanaverage, with several dangerous cold snaps possible. However, fall may be warmer-than-average, with the cooler weather holding until winter and early spring.

Southwest: The driest of these states will be Utah and Arizona, which have a historically low likelihood of moisture throughout the period. Northern and northeastern Colorado has the highest chance for moisture and historically has a 70 percent chance of a wet period. The region in total, however, only stands a 30 percent chance of a wet period. Temperatures for eastern Colorado will have the potential to be cooler-than-average, with some dangerous cold periods to come through for producers. Most of the region, however, will be warmer-than to near-normal.

Upper Midwest: This region in total will end near-average in terms of precipitation. The region's northern half is likely to be wetterthan-average; meanwhile, drier-than-average conditions are more typical in this setup for the southern half, which is much of Iowa. Temperatures will be cooler-than-average, with several dangerous cold snaps possible.

South: Kansas, Oklahoma, and western Texas lean drier-thanaverage in this setup. These areas have less than a 30 percent likelihood of a wet outlook. Parts of eastern Texas, Arkansas, Louisiana and Mississippi favor some periods of wetness and historically have a 70 percent chance for above average moisture through spring. Computer modeling agrees with the historical assessment. Temperatures may end up cooler-than-average during the period; look for strong cold fronts to push south occasionally. Dangerous cold is a possibility as it was in early 2021.

Ohio Valley: Missouri is likely to be the driest of these states, followed by Tennessee. Moisture will favor southern Illinois, Kentucky, Indiana, and Ohio – with western Kentucky being the most wet. West Virginia leans slightly wetter-than-average, historically. In all, this region will break even; moisture will favor the eastern areas. Temperatures will be normal-tocooler-than-average.

Northeast: This region will break even in terms of moisture. Historically, and in forecast modeling, these areas will experience hit and miss pockets of moisture. Nor’easter events will need to be watched for significant moisture in a short time along the coasts and for parts of inner New England, too. Far northern areas of this region are most likely to be warmer-than-average.

Southeast: Tropical systems through fall will be the best chance for moisture here, and that was the primary source of moisture in those most similar years in the past. Barring tropical activity, this region has a 40 percent chance of a wetter-than-average period. South Florida is usually the driest of all zones. Wetness has been more frequent for those in the northern parts of this region. Temperatures are likely to be near normal.