Higher-than-normal risks of early frost
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.