La Nina brings below normal precipitation and above normal temperatures
for The Fence Post
After fall harvest winds down, the big question for farmers and ranchers is what will La Nina bring for this winter in the Rockies and central Plains states?
“La Nina is here, and not going anywhere. Still looking very dry on the Plains this winter,” said Kyle Mozley, meteorologist at the National Weather Service in Pueblo, Colo.
The Climate Prediction Center’s early Winter Outlook issued Thursday, Oct. 15, 2020, is forecasting cooler and wetter weather in the northern states, and largely warmer and drier weather in the southern states. However, being smack in the middle from Colorado to Wyoming, and into the central Plains the National Oceanic and Atmopheric Administration favors near to slightly below normal precipitation, and near to slightly above normal temperatures across the central Plains.
Looking at past moderate events, the upper pattern features ridging over the western U.S. and troughing over the east, with northwesterly flow across Colorado.
“Areas of the Pacific Northwest and Ohio Valley will likely do well this winter, while leaving Colorado and Kansas warm, dry and windy, typical for La Nina in the Rockies into the central Plains,” said Mozley, adding, “This matches up with the CPC forecast with warm and dry conditions across Colorado into Kansas, not good for our already drought stricken-rangelands.”
It has been exceptionally dry for the past six months across eastern Colorado and western Kansas.
“In fact, for the past 30 days, all of eastern Colorado has seen 0 to 5 percent of normal precipitation, meaning none to maybe a few hundredths at best, and western Kansas was slightly better at about 30 percent of normal. Soil moisture is also pretty terrible right now, with 87 percent of the state short or very short of moisture in the top 6 inches,” Mozley said. “Needless to say, our rangelands are in very poor condition heading into winter. Drought is prevalent across all of Colorado into western Kansas, with the western part of Colorado in D3-D4, while the eastern Plains are in D2-D3, with no improvements expected, and conditions likely getting worse this winter.”
Agricultural impacts could have likely resulted when much of the Colorado plains saw an early freeze when a storm brought snow to the region. While temporary, the freeze conditions were about three weeks early, compared to previous years.
La Nina’s cooler-than-average sea surface temperatures continue across the central and eastern Pacific Ocean near the equator. It is the opposite of El Nino. Forecasters believe this weak-to-moderate La Niña will continue to strengthen, peaking around December, and persisting into the spring 2021.
“With sea surface temperature anomalies (departure from normal) falling to around -1.6 degrees Celsius, with a few slightly colder, I’m still thinking anomalies staying around -1.6 degrees C heading into January, before they begin to rebound (although still well in La Nina threshold) this spring,” Mozley said.
However, there is a hopeful sign for moisture.
While the climate pattern Pacific Decadal Oscillation (PDO) will continue in a negative phase through the winter, likely enhancing warm and dry across Colorado, another climate driver the Madden Julian Oscillation forecast (an eastward moving disturbance that traverses the planet) has potential for a brief stormy pattern in late November to early December (around Nov. 24-Dec. 10). While the overall outlook is for dry, drought conditions into spring, the Arctic Oscillation (AO) could also bring surges of colder air to the Plains, Mozley said.
With temperatures already in the low 20’s and some snow already seen in parts of Wyoming, summer has been doing somersaults over autumn.
With drought reported to be occupying 45 percent of the U.S., largely over the western half of the country (but also in the northeast) many are anxiously hoping for moisture. However, currently most of Wyoming (almost 90 percent) is in one level of drought or another with the northwest part of the state being the only area in either pre-drought (D0) or no drought.
“Over 97 percent of Wyoming is impacted. Teton is the only county that has no drought or pre-drought in it. Given the precipitation expectations and with above normal temperatures expected for at least the next several weeks statewide (and for the upcoming months in the southwest) drought conditions, especially in the southern half of the state should be expected to continue and intensify,” said Tony Bergantino, interim director of the Water Resources Data System at the Wyoming State Climate Office and Wyoming Community Collaborative Rain, Hail, and Snow state coordinator.
In the short-term, after some brief cold and wet conditions continuing through October, Wyoming will be again looking at higher chances for above normal temperatures for November and for the November to January period.
“After that the signal gets weaker and the only real guidance is for the southwest and the northeast parts of the state. The southwest will continue to have better odds of experiencing above normal temperatures while the northeast has somewhat better chances of seeing below normal temperatures and this pattern continues into spring,” Bergantino said.
Thankfully, for November through January, there are actually greater chances of above-normal precipitation for the northern half of Wyoming, which brings hope. The chances in the southern half are equally distributed between above normal, below normal, or normal.
A Nebraska meteorologist sees some positive signs for moisture, even during a La Nina winter. Instead of just cold and drier, that means Nebraska and the central Plains could expect a lot of ups and downs temperature-wise and the windy conditions those weather systems will bring. Then also, despite the relative confidence in the impacts of La Nina on the upcoming winter, the weather across Nebraska and Kansas may end up a bit of a mixed bag, especially in terms of temperature.
“Also, during La Nina influenced winters, temperatures often vary widely from above to below normal thanks to frequent weather systems rolling across the central Plains from the northwest. Long range precipitation outlooks are notoriously difficult, but the impacts of La Nina can be somewhat helpful in looking ahead. Typically, during La Nina winters, precipitation on the central Plains is no more than normal, and often below normal. La Nina also impacts precipitation timing, with wetter conditions in December and January, and the drier months during the second half of the winter (February and March),” said Michael Moritz, warning coordination meteorologist for the NWS in Hastings, Neb.
Should warmer than normal temperatures and near or below normal precipitation occur, the winter ahead is likely to result in expanding drought conditions across the central and southern Plains, including Nebraska and Kansas. “NOAA expects drought conditions to worsen in areas already hit hard by drought, and for drought conditions to expand from Nebraska to Texas by mid-winter. With depleted soil moisture already, the impacts of drought could spill into next spring,” said Moritz.
It will really boil down to whether the La Nina dissipates next spring or is able to maintain itself for a second consecutive year. Right now, all of the models end La Nina by late spring.
“If this is the case, above normal snowfall across the northern Rockies the first half of the winter would tend to mitigate the upper air ridge strength over the southern and central Rockies as the winter progresses. Therefore, the opportunities for upper air energy to move into the Pacific Northwest and dig into the central Rockies increases, and this is the most likely time frame to see large snow and precipitation events to return to the southern and central Plains region,” said Al Dutcher, agricultural extension climatologist in the Nebraska State Climate Office in Lincoln, Neb. “However, if this La Nina gets stronger than forecast and holds on longer into the winter with moderate strength, precipitation in this region is likely to be sparse until mid-spring at the earliest.”
Kansas Climatologist Mary Knapp points out that precipitation in November is critical to maintain and establish fall planted crops, including winter wheat, canola and cover crops.
“Even wetter than normal conditions are unlikely to improve the current drought conditions,” said Knapp, assistant state climatologist at Kansas State University in Manhattan.
Kansas is expected to be on the dry side this winter, but that doesn’t necessarily mean quiet. “Strong (cold) fronts are still likely, bringing high winds without much moisture. This increases the likelihood of dust storms (such as last weekend), and high fire danger,” Knapp said.
Knapp’s other take-aways from the CPC Winter Outlook:
• It is dry and getting drier.
• Warm temperatures, low humidities and windy conditions are increasing evaporative demand, drawing down stock ponds at a faster rate than usual at this time of the year.
• Given the normally dry nature of winter even above normal precipitation may not reduce the drought.
For more information, go to http://www.cpc.ncep.noaa.gov/products/predictions/long_range/lead01/off01_prcp.gif or https://www.cpc.ncep.noaa.gov/products/predictions/long_range/lead01/off01_temp.gif. ❖
— Hadachek is a freelance writer who lives on a farm with her husband in north central Kansas and is also a meteorologist and storm chaser. She can be reached at firstname.lastname@example.org.