Hot, dry conditions to persist in some areas
for The Fence Post
For ranchers and farmers in the Rocky Mountain states and the Central Plains, any rains will be welcome, with the predicted drier Autumn season.
Fall 2020 favors warmer-than-normal temperatures, coupled with lower-than-normal precipitation, according to NOAA’s Climate Prediction Center, which released its forecast for September, October and November, on Aug. 20.
“Looking ahead to September through November, warmer-than-normal autumn weather is most likely across the southern High Plains and the Southwest. Drier-than-normal autumn conditions from the Great Basin to the central and southern Plains should contrast with wetter-than-normal weather across portions of the northern Plains and the Northwest,” said Brad Rippey, USDA meteorologist in the Office of the Chief Economist-World Agricultural Outlook Board in Washington, D.C. “Such a precipitation pattern (drier to the south and wetter to the north) would be consistent with conditions typically observed during the autumn development of La Niña.”
Due to a lack of sufficient rains from Colorado to western Nebraska and western Kansas, during the three-month period ending Aug. 18, hot, dry weather fueled rapid drought intensification in many areas from the Southwest to the High Plains, with reductions in topsoil moisture and significant stress on rangeland and pastures.
“On Aug. 16, topsoil moisture was rated at least one-half very short to short in Texas and all 11 western states except for Arizona. On the same date, very poor to poor ratings were noted on more than one-half of the rangeland and pastures, specifically for: Colorado: 55 percent, Wyoming: 65 percent, Oregon: 67 percent, and California: 55 percent,” Rippey said.
Another climatologist linked the latest forecast to “a planet that is warming.”
“Temperatures going up, water temperatures increasing, and glacial ice in Greenland is decreasing at high latitudes with the water running off into the sea which is rising. When we look at the climate outlook that came out today — warmer than normal toward the four corners (southwest U.S.) and the central and southern Plains — that’s not really unexpected as we go forward, with the warming world,” said Sean Sublette, meteorologist with Climate Central, an organization that analyzes and reports on climate science. “With higher temperatures, there’s more evaporation off your soils, if your water resources haven’t been more plentiful.”
It’s a similar story of above normal temperatures and below normal precipitation for eastern Colorado heading into December. Also, the latest drought monitor has D3 category covering much of the western slope. The eastern Colorado plains are solid D2 with pockets of D3.
The U.S. Drought Monitor Drought Intensity Scale has five categories; D0, D1, D2, D3 and D4. D0 is abnormally dry, then D1 is moderate, D2 is the severe drought category where crop or pasture losses are likely, fire risk is very high, and water shortages are common, D3 is extreme and D4 is exceptional drought.
However, there is hope for some relief.
“The monsoon pattern (seasonal reversing wind) with high pressure over the Four Corners should break down late this coming week (around Aug. 28). This may bring a few days of increased chances for precipitation for eastern Colorado, although not enough to make up for the past few months’ lack of rainfall,” said Kyle Mozley, meteorologist with the National Weather Service in Pueblo, Colo. “Looking at the Plains precipitation from June to July, most are running about 60-80 percent of normal. There are a few exceptions, mainly east central counties (like Kiowa) which are running near 100 percent of normal.”
Regarding a key climate driver, Mozley predicts La Nina is coming.
“In fact, I would expect us to be in actual La Nina conditions by October, and prevailing through the first part of the year,” he said.
Unfortunately, La Nina is typically considered bad for Colorado, Mozley noted, especially for the La Garita and San Juan ranges, except however for the central mountains where favorable orographics would help the mountain influence that forces an airmass upward and more persistent northwest flow.
“For the December to February period, almost every (weather computer model) site I have worked on, (a negative Arctic Oscillation, negative Pacific Decadal Oscillation, and negative Pacific North American teleconnection and others) have greater than 125 percent of normal during La Nina for those months,” said Mozley, noting, that typically for Colorado, this would lead to windy and warmer conditions. “For the winter, watch out for December to February above normal precipitation in the mountains, especially with negative AO, PDO and PNA. Then drier March to May.”
So, the problem then becomes beyond February, where most mountain locations receive a bulk of their heaviest snowfall, it shuts off with a dry spring,” Mozley said.
“So in conclusion, for the next two weeks, drier and hotter than normal, but with a pattern change coming mid to late next week (Aug. 26-29). Overall, continued warmer than normal, and drier than normal, especially across the Plains.”
The most encouraging climate news for Wyoming, is above normal precipitation predicted briefly for late August into September, and again late Autumn. Here is the specific analysis for Wyoming from Tony Bergantino, interim director for the Water Resources Data System — Wyoming State Climate Office/Wyoming CoCoRaHS State Coordinator.
“Warmer temperatures are expected across Wyoming in the short-term although there could be a brief respite looking out the following week where there are better chances for the northern two-thirds of the state to be below normal,” he said. “Above normal precipitation is favored the next two weeks over most of Wyoming, except the southwest, the following week.”
“Precipitation would be very welcome here where just over 92 percent of the state is in D0 (Abnormally Dry) or worse conditions,” Bergantino said. With over 5 percent of the state in D3 (Severe Drought) that’s the first D3 since Oct. 9, 2018, and the largest areal extent since Sept. 24, 2013. Unfortunately, drought conditions are expected to persist over most of Wyoming, as the fall outlook predicts above normal temperatures into the November to January three-month outlook, according to Bergantino.
September is expected to have below-normal precipitation, with chances higher in the southern quarter of the state. From September to November, there are equal chances of having either above, below or normal precipitation.
“Finally, October to December and beyond offers slightly better chances for above normal precipitation, mostly for northern Wyoming, then reaching further south,” Bergantino said.
There’s another encouraging possibility for precipitation, concerning a lean toward a La Nina.
“Sea surface temperatures in all of the Nino regions of the Pacific are average or just below average, they have not dipped below the threshold to be considered a La Nina event, although there is a 60 percent chance of this happening in the fall and about a 55 percent chance of it continuing into the winter 2020 to 2021. During La Nina conditions, the jet stream can bring cooler air down from the north into parts of Wyoming and the chance that parts of Wyoming could see above normal precipitation which is shown in the three-month outlooks,” Bergantino said. “Unfortunately, these are not hard and fast rules.”
Specifically for Nebraska and Kansas, odds clearly favor warmer than normal temperatures across both states with southwest Kansas having the highest likelihood of above normal temperatures.
Precipitation has been more “hit and miss” across Nebraska and Kansas this summer, and the region has seen an expansion of drought conditions the past two months.
“This outlook favors drier than normal conditions across southern Nebraska and all of Kansas in September, October and November. Northern Nebraska may fare a bit better with near normal precipitation,” said Michael L. Moritz, warning coordination meteorologist with the National Weather Service in Hastings, Neb.
“Should the drier and warmer than normal weather materialize as anticipated, winter wheat emergence could be impacted along with surface water flows. This outlook of average to below average precipitation will also likely worsen drought conditions,” Moritz said, adding, “Though wildfire concerns tend to diminish in late fall, the region will likely experience higher fire danger conditions through mid-November if widespread rain doesn’t occur.”
Meanwhile, the southern Rockies upper air ridging is also expected to continue strengthening and build northward through the fall.
“This would result in poor subsoil moisture return across the western half of the states from Texas northward through Nebraska. This is essentially west of a north/south line from Kearney, Neb., to Mexico,” said Al Dutcher, agricultural extension climatologist, Nebraska State Climate Office.
With a La Niña watch issued, the outlook favors continued neutral conditions during the summer, with a 55 percent chance of a La Niña by autumn, said Mary Knapp, assistant state climatologist located at Kansas State University in Manhattan, who worked in partnership with Chip Redmond, meteorologist and Weather Data Library network manager. “A La Niña event typically brings warmer and drier-than-normal conditions to the Plains during late summer and early fall,” Knapp said. “This type of pattern would be favorable for finishing summer row crops and harvest, but could be troublesome for establishing winter crops like winter wheat and canola. An increased chance of warmer/drier doesn’t mean a cooler/wetter or normal period is out of the question — they just have lower probabilities.”
The coming months are a transitional season, Knapp said. “During the fall, average temperatures fall daily and normal precipitation amounts are decreasing as we approach the coldest and driest period of the year for Kansas,” and other states.
A wild card for the autumn forecast is the expectation for a very active Atlantic Basin hurricane season. The Pacific hurricane season could bring hope for some rain.
“Moisture from former eastern Pacific tropical cyclones can occasionally contribute to enhanced autumn rainfall, primarily across the southwestern and south-central United States.” That would be welcome news for the southern Rockies and southern Plains. ❖
— 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.