Warm dry spring expected
March 22, 2018
Eyebrows are being raised — with some climatologists predicting a fairly warm and dry spring forecast for the eastern plains of Colorado, eastern Wyoming and the central plains states, and another climatologist predicting a possibly stormy spring.
For starters, this spring is unique because this is an unusual second consecutive year of La Nina, which typically points to dry and warm conditions, although this doesn't always materialize, as one or two big spring storms can really change the numbers. As climatologists and meteorologists offer up a few different forecasts and theories, here's what's on the table this spring for farmers and ranchers regarding expectations of moisture and temperatures.
"One thing that has made this La Nina interesting is that we are in our second straight year of La Nina. It's not unheard of by any means, but we haven't observed a particularly large number of second-year La Ninas either. The second year La Ninas we have seen tend to be cool and wet in the northwest and northeast corners of the country, and milder and drier everywhere else. The last one we saw was 2012," said Peter Goble, research associate with the Colorado Climate Center on the campus of Colorado State University in Fort Collins.
La Nina is defined as a period of five consecutive (three-month) seasons when the equatorial Pacific Ocean water is cooler than normal (by more than 0.5 degrees Celsius). The La Nina typically produces drier weather in much of the U.S. However, the reverse; El Nino, would exist if five separate (three-month) seasons feature water warmer than 0.5 degrees Celsius. Subsequently, El Nino conditions would then normally help produce wetter conditions.
The official spring outlook from the Climate Prediction Center for Colorado in April, May and June is an increased likelihood of above normal temperatures for eastern Colorado, with a greater likelihood to the south. "The southeast and central east plains have particularly dry soils right now down to 1-3 feet (think: south of Akron). The soil moisture is looking better out towards the northeast corner of the state," Goble said adding, "Of course, the new CPC outlook (issued March 15) for April to June temperatures is based on more than just soil moisture, but you'll notice the odds of a warmer than normal April/May/June are higher for southeast Colorado, than northeast Colorado."
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This official 90-Day outlook also indicates an increased chance of above average spring warmth from western Kansas into western Oklahoma. Then, for north central Kansas and eastern Kansas, there's a slightly lower possibility of warmer than average spring temperatures. Southern Nebraska and much of Iowa have even lower chances for a warm spring, and in fact, have close to equal chances for either average, above or below average temps.
Further north, from the northern half of Nebraska into northwest Iowa, closer to normal spring temperatures are expected.
Interestingly, regarding precipitation, much of the central U.S. is forecast to have equal chances of either above, below or average precipitation this spring. In other words, close to typical moisture amounts are predicted for Kansas, Nebraska, northeast Colorado, eastern and northern Wyoming, southern Montana, and also for Missouri and western Iowa. Eastern Iowa has a slightly greater likelihood of above average precipitation.
"Although a weak La Niña is expected to continue through the spring, the influence lessens as we move into summer. This can be seen in the latest three-month outlook for April-June, which has a neutral outlook for precipitation in most of Kansas," said Mary Knapp, assistant state climatologist at Kansas State University, Department of Agronomy, Manhattan, Kan. "Even with normal precipitation, it would take some time to improve the current drought situation in the central and southern plains."
MORE PRECIP, COOL TEMPS
La Nina, especially in winter typically triggers cool temperatures and above-average precipitation in the northwest, and below-average precipitation in the southwestern U.S.
"Wyoming often finds itself being in a transition area from north to south between the two. Not all La Ninas are the same and the strength of one has a major effect on the pattern produced. The current La Nina is also diminishing and conditions are heading toward ENSO-neutral (neither La Nina nor El Nino) probably in this April-June time-frame," said Tony Bergantino, deputy director, Water Resources Data System – Wyoming State Climate Office and Wyoming CoCoRaHS State Coordinator. "Unfortunately, with Wyoming in the boundary area and with La Nina becoming quite weak now, signals can be mixed or indeterminate," Bergantino said.
"Specifically for precipitation, while the odds favor the southern part of Wyoming (roughly the area south of a line running from the southern Yellowstone National Park down through the Laramie area) being drier than normal, the rest of the state north of that line has even chances for normal, above-normal or below-normal precipitation. Very much a similar situation occurs for temperatures with approximately the southern half to one-third of Wyoming having better chances for above-normal temperatures while the northern half to two-thirds of the state has no signal one way or the other," Bergantino said. Regarding the April-June period for eastern Wyoming, Bergantino expects a greater chance of warmer temperatures in the southern third of Wyoming with the signal making a forecast indeterminate for the northern two-thirds. For precipitation in eastern Wyoming for that same period of time, drier than normal conditions are only slightly favored for a small part of the south, and unknown for everything north of that.
COOL AND ACTIVE
There's a different theory from Nebraska Climatologist Al Dutcher, who said if the ongoing pattern of low-pressure systems continue to approach the central plains (northern Kansas and points north) and Midwest (upper Mississippi River valley, Great Lakes and Ohio River valley) these areas could see cool and active weather, should it continue.
"The last two upper lows (low pressure systems) produced respectable precipitation on the north and east side of these upper air lows. The south and west sides of these systems have been able to pull in the dry air from the southern plains (dry slot) and wrap it around these low pressure systems, effectively cutting off precipitation on these two flanks of the storm. Thus, even though parts of central Kansas are experiencing very welcome moisture, the western one-third of Kansas as well as Oklahoma and Texas received none to very light (less than a half-inch) of moisture," said Dutcher, associate state climatologist for the Nebraska State Climate Office in Lincoln.
Meanwhile, Dutcher said snowpack continues to disappoint across the southern Rockies, with only very limited relief to no relief so far for the worst hit areas of the southern U.S. winter wheat belt.
"Snow recovery for the southern Rockies is highly unlikely, as we are near the statistical peak of their snowpack season. I expect complete melt out of the snowpack for New Mexico and the southern one-third of the Rockies before the end of May," Dutcher said. "Temperatures are now reaching the 70s and 80s across the southern wheat belt and those temps also extend westward into the lower elevations of the southern Rockies. That's the problem across the entire southern half of the Rockies, low snow at low elevations, normal to below normal snowpack at the highest elevations." He expects low elevation snow values to melt out earlier and increase high elevation melt out quicker, instead of a buffering rapid melt out.
Dutcher said, as long as there's normal moisture this spring, Nebraska could still escape significant drought implications. "If the central Rockies is to maintain normal snowpack through early May, it will translate into a very wet pattern for the west central corn belt (Kansas, Nebraska). This would also be supportive of severe weather, as upper air lows associated with this type of pattern eject from the southern Rockies, head northeast and develop storms on the north side of the warm front, as well as, along the cold front. These systems are usually responsible for our most significant tornado outbreaks," Dutcher said.
The Climate Prediction Center outlook also shows that the Pacific Ocean is likely to return to neutral conditions during the March-May season, Goble said. "But it's still more likely than normal that we'll see a warm, dry spring. The eastern Plains have been very dry recently, and it's easier for the sun to quickly warm dry soils than wet soils, so that's another piece of the puzzle," he said. "Seasonal forecasting is also more difficult than forecasting the weather tomorrow, so it doesn't hurt to be ready for anything." ❖