Weather watchers predict mostly above normal temps and precipitation this fall
For more information:
(Wyoming’s) July Climate summary at: http://www.wrds.uwyo.edu/drought/reports/outlook.html
As summer begins winding down with its interim drought busters and summer monsoon season, ranchers and farmers in the Rocky Mountain states and in the high Plains are now intently focused on the newly released fall weather forecast. Just revealed Aug. 15, the Climate Prediction Center’s outlook for September/October/November 2019 includes interesting scenarios about the rapidly-approaching autumn season.
With hopeful eyes on a potentially positive snowpack this fall into winter, Colorado’s three-month autumn forecast from the CPC includes slightly greater possibilities for snowfall, but then also possibly above average temperatures. Then there’s the “wild car” thrown into the mix, which is the long-drawn out El Nino phenomenon that recently transitioned to an ENSO-neutral phase.
“The outlook for September, October and November continues to show 40-60 percent chances of having above normal temperatures for all of Colorado during the fall months.
There is a 33-40 percent chance of above normal precipitation for almost all of Colorado, except for extreme southeast Colorado, where there are equal chances of (having either) above normal, normal, or below normal precipitation,” said Jennifer Stark, meteorologist-in-charge at the National Weather Service in Pueblo, Colo.
Regarding ENSO (formally called El Nino Southern Oscillation,) NOAA recently issued its “Final El Niño Advisory” noting this ENSO-neutral is likely to continue through the Northern Hemisphere from winter 2019-20 (50-55 percent chance). NOAA’s latest computer model guidance reveals there are many possible outcomes for the upcoming winter season. Not only is this rare for this time of year, but it yields great uncertainty in whether ENSO-neutral conditions will dominate, or if El Niño conditions return. Interestingly, the least likely scenario is for La Niña conditions to emerge.
“We continue to be in an ENSO-neutral phase. Generally, ENSO neutral means that we can expect a near to slightly below average snowfall for the central mountains, below normal snow season for the southwest mountains,” Stark said, noting that, “Generally, the Pikes Peak region and eastern Plains will have a little more variability in the weather this fall, but we should have near average precipitation.”
All of Wyoming has a similar outlook to Colorado’s for September thru November, as most of Wyoming is also expecting generally good chances for above normal precipitation and above normal temperatures.
“For temperatures, the chances get stronger in the south and southwest while, for precipitation, the chances are highest in about the eastern third of the state. Unfortunately this means that the area west of the “Divide” which hasn’t had as much of the benefit from precipitation lately, will have the highest chances for above-normal temperatures with odds not as high for the area to receive above-normal precipitation,” said Tony Bergantino, deputy director of the Water Resources Data System for the Wyoming State Climate Office and Wyoming CoCoRaHS state coordinator. “As a consequence, the drought conditions there, could continue and increase in the near term.”
With sea surface temperatures above average in the western and central Pacific Ocean and below average in the eastern parts making ENSO conditions neutral, this doesn’t necessarily mean an average winter. “But, rather, that without a strong La Nina or El Nino signal, longer-term predictions can be more difficult,” Bergantino said.
This autumn, the central Plains states are expecting slightly above average temperatures and also slightly higher than average precipitation amounts, according to the CPC’s recently released three month forecast.
“NOAA’s outlook for September-October-November in the central Plains which modestly favors above normal temperatures, could potentially spell a later-than-normal first freeze, although this is not necessarily assured. As for precipitation, the fall outlook slightly favors above normal amounts across the majority of Nebraska and far northwest Kansas, but the majority of Kansas along with southeast Nebraska has been assigned “equal chances” of observing either above normal, below normal or near-normal precipitation,” said Ryan Pfannkuch, meteorologist for the National Weather Service in Hastings, Neb., who researched the climate outlook along with colleague-NWS Hastings meteorologist Shawn Rossi. “In short,” Pfannkuch said, “This means that long range forecast tools do not present enough of a signal to support one of these possible outcomes over another.
The trend towards ENSO-neutral conditions began in July and has continued into August.
“Interestingly, ENSO-neutral would often tend to favor below normal precipitation across the central Plains during the fall. However, due to higher-than-normal soil moisture content in most areas at this time, if anything the official forecast slightly favors above normal precipitation in parts of the region (most of Nebraska and far northwest Kansas),” Pfannkuch said. This is due in part to the concept of “moisture recycling,” which basically means that areas have been wet for a sustained period of time tend to stay wetter as long as overriding weather factors don’t kick in.
Nebraska Climatologist Allen Dutcher observed that the Plains region could receive typical or ample moisture, although he cautioned that this doesn’t mean the horrific wet conditions of late 2018 into 2019.
“I see that the trough/ridge pattern will persist into the foreseeable future, where troughs entering the Pacific Northwest ‘butt up against’ the southern Plains/Rockies upper air ridge, then ride over the top of the ridge to carve out a trough in the eastern corn belt. This has been occurring on a 10-14 day cycle the past two months and I expect it to continue into September,” said Dutcher, associate state climatologist for the Nebraska State Climate Office in Lincoln. “For Nebraska and Kansas, ‘the jury is still out’ on cool air infiltrations from the north, but I do see the troughs entering the Pacific Northwest as the real wild card going forward; digging a little further south and that sets up the Plains regions (central and southern) in a favorable position should these troughs continue to dig further into the central Rockies. This would help low pressure systems strengthen at the surface in southeastern Colorado/Texas Panhandle and head northeast, drawing Gulf of Mexico moisture northward. Although I am not calling for the wet conditions we saw last fall, I do see above normal moisture as a distinct possibility,” Dutcher said.
The big chatter now from farmers, Dutcher said is concern about late planted crops and above normal freeze risk. So, a cool September will only strengthen these concerns. I continue to believe, based on the trends of the past two months), that an early freeze is likely over the northern Plains (Dakota’s and western Minnesota.) I would place an elevated risk for an early freeze for Nebraska, Iowa, Illinois, Indiana and Ohio,” Dutcher said.
Dutcher hopes the CPC 90-day above normal temperature forecast verifies and reduces/eliminates concerns for an early freeze. “But I will remind folks that it would be highly unusual to see the entire U.S. come in average or above average during the September-November period. This is especially true this year, where there have been distinct areas of below and above normal temperatures, so I wouldn’t expect to see the pattern change on a dime from persistently cold conditions for almost four months of CPC forecasts for the upper Midwest to one that favors widespread warmth.”
Another ag concern is increasing evidence that a potential cooling of the Equatorial Pacific is underway. “If this continues, La Nina development will need to be watched for, as we progress into early winter. Although it shouldn’t have a huge impact on fall conditions, it could portend to drier conditions developing across the central/southern Plains as the winter progresses,” Dutcher said.
While Kansas continued to be wet in the east, the western and central parts of the state have been drier than normal. So, soils in these areas have continued to dry.
“The outlook for September calls for continuation of that pattern with an increased chance of wetter than normal conditions across the state. The temperature outlook favors an equal chance for a warmer or cooler than normal pattern across the entire central Plains. A normal or slightly below normal precipitation pattern for September would be favorable in the eastern divisions, where saturated soils continue to present problems. Cool temperatures would slow the normal drying pattern,” said Mary Knapp, assistant state climatologist at Kansas State University in Manhattan.
Knapp noted, while slightly cooler temperatures could reduce heat stress, it would also increase disease pressure. “Degree day accumulation will be the biggest concern, as late planted crops are still lagging in maturity.”
Also, as the fall temperature outlook switches to warmer than normal temperatures across the state, this however, doesn’t indicate how those temperatures might be distributed. Another consideration is with above normal precipitation, surface moisture is abundant, which increases humidity and thus, the heat index as well. “Heat indices will be quite high despite cooler than normal temperatures (September normal high temperatures typically reach low-to-mid 80s for much of the state),” Knapp said.
Chances of precipitation also fall in to the equally likely distribution.
“A slightly drier than normal fall, with well distributed rains would be much more beneficial than a continuation of the rainy pattern. Although harvest is likely to be later than usual, given the lateness of the crops, a dry pattern would allow for a more rapid harvest than last year. The western third of the state has drier soil moisture at the surface, and would benefit more from average precipitation, particularly to establish the fall seeded crops such as winter wheat and canola,” Knapp said.
Additionally, Knapp said that increased evaporation and atmospheric moisture, would increase the likelihood of additional heavy thunderstorms and rapid rain rates across the region when rainfall does occur therefore, “Flooding risks will remain elevated for much of the fall — even when dry periods develop between rain events.” ❖
— 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.