Higher-than-normal risks of early frost
Editor’s Note: We want to thank Drew Lerner, Doane’s weather consultant and President of World Weather Inc., for allowing us to share this version of a special report he sent to commercial clients last week regarding early frost risks.
Worry over the potential for early frost and freeze conditions in North America has started to rise significantly in the commodity trade this week and rightly so. With crops planted late and maturing late, there is potential for notable crop production cuts in a seasonably normal frost and freeze event, let alone one that is earlier than usual. It caught my attention as a meteorologist big-time when the low at Bismarck, ND sank to 39 degrees on July 26!
Weather patterns this summer have not allowed the Northern Hemisphere to warm up normally and reports from the arctic suggest ice accumulations are way ahead of recent years. A recent report from the polar region shows the number of above freezing days this summer was reduced by nearly half. These issues, along with the ten-day, 30-day and 18-year cycles all add merit to the mid-July CFS model prediction for a couple “threat periods” for early season frost and freezes in September. (But I must caution the CFS model “track record” for accurate temperature forecasts six weeks in advance is not very good.)
Other early warning signs: Low temperatures Aug. 14th in portions of Wisconsin and Minnesota slipped to the middle 30s, the day after similar lows occurred as far west as northeastern North Dakota. This cool period also followed some patchy soft frost reported in a few Saskatchewan, Canada locations a few days before that. It had been roughly three weeks since the last bout of unusually cold nighttime lows (18 to 19 days to be precise). Normally, when unusually cool weather patterns occur in late summer, observing the rhythm in which the cold bouts occur can sometimes be the best indicator of when the next bout of cold will arrive. If that is true in this case, the first days in September will need to be closely monitored for the next bout of coolness in Canada’s Prairies and/or the northern U.S. Plains.
The 18- to 19-day interval between cold shots is also close to the second occurrence of the 10-day cycle, which fits well in the general timing of weather events in the atmosphere. But again, I must caution that predicting the first frost and freeze event of the year is one of the greatest challenges put to a meteorologist and/or climatologist since it requires predicting temperatures within two to three degrees of accuracy 6 to 8 weeks ahead. And the difference between a damaging frost or freeze event and one of only minor consequence to yields is often determined by a degree or two in temperature. But with that said, there are a number of issues that need to be discussed in this report that reinforce prospects of early season frost and freezes.
1974 Should Not Be Forgotten. Many parallels to past years are often tossed about when weather becomes extreme and one of the years of comparison for 2013 has been 1974. Much like this year, planting of many spring crops was late due to a cool and wet weather pattern. Crops were far behind in their development most of the growing season. And like this year, there was then a short term bout of warming and generally favorable mid-summer weather and crop conditions improved. But there was a Labor Day weekend freeze that was devastating. And this year the similarities to ’74 don’t stop with a wet spring and late planting. Summer 1974 turned drier than usual in the northern half of the Plains and in a part of the upper Midwest. Just like this year, the drier biased areas included the region from Kansas to North Dakota, including western Iowa. The driest areas this year were a little further to the east and north over those in 1974, but similar enough to be a valid analog. The key difference is that the cool weather in August 1974 was mostly in the Plains, Midwest, Delta and southeastern states, whereas this year the coolest area has been the upper Midwest, Great Lakes region and immediate neighboring areas.
World Weather, Inc. is not “predicting” a ’74-like freeze. We’re just noting that the atmosphere was in a cooling mode back then as it is now. The similarities are so strong we cannot write off the ’74 freeze as a fluke. Even the solar cycle was trending in the same direction of reduced sunspot numbers similar to that we’ve seen in recent years. There have also been reports of earlier than usual ice accumulation in the higher latitudes in the polar region. Both of these observations reinforce the thought that 2013 warming in the higher latitudes failed to occur as normal, leaving the arctic with greater than usual amounts of cold air for so early in the coming cool season. That cooler-than-usual air in the arctic will be funneled to the lower latitudes, periodically when strong ridges of high pressure build up around the Northern Hemisphere at times - forcing the colder air southward into crop regions.
Atmospheric cycles also suggest early and late September may be the more favored periods for threatening cold. These two periods are identified in the 10-day cycle. The fact that mid-August cold occurred 18 to 19 days after that which occurred July 26 suggests that if the cycle repeats again, the first days of September will represent the next more threatening period of cold for Canada’s Prairies and the northern Plains. Another 18 to 19 days after that puts another bout of potential threatening cold into the north-central United States after September 22.
Concluding Remarks: The research referenced here raises some evidence that the bias may be tilted toward an earlier than usual frost and freeze event. The evidence of this is not totally convincing, but high enough that we wanted to make sure our clients realize “potential” for damaging freeze is higher than usual and to plan accordingly.
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