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Tech Guy on La Nina & Flash Drought for 7/3/22

More details on La Nina for those interested - I found this article on Progressive Farmer.

La Nina will not go away. The cool-water phase of the equatorial Pacific Ocean temperature and atmospheric pattern is now in its third year, and summer 2022 shows the strongest La Nina atmospheric measurement of this multi-year run for this point in the year. The atmospheric component of La Nina is noted by the Southern Oscillation Index, which is usually referred to as the SOI. The SOI tracks the relationship in barometric pressure between the island of Tahiti in the central Pacific Ocean and the city of Darwin in the Northern Australia Territory. A post from NOAA's explains that the SOI "compares the difference from average air pressure in the western Pacific, measured in Darwin, Australia, to the difference from average pressure in the central Pacific, measured at Tahiti...During La Nina (positive SOI), the pressure is higher than average over the central Pacific near Tahiti, and lower than average over Australia. During El Nino, the SOI is negative, and the anomalies are reversed." The Pacific circulation numbers are definitely in the La Nina phase. The 30-day SOI moving average as of June 30, 2022, was plus 19.3. That value is considerably higher than in late June of either 2021 or 2020 when the SOI value was around plus 2.0.

La Nina during the U.S. growing season is a challenging crop weather maker for corn going into pollination--which is still ahead for the majority of the corn crop. When La Nina is in effect, upper-atmosphere high pressure tends to be the dominant feature during the midsummer period. That upper-atmosphere high is, in turn, a pattern that brings drier and hotter conditions to the central U.S. If soil moisture is short when the dry and hot pattern sets in, corn pollination can be affected, and lower yield is possible. Prospects for this kind of stressful heat and dryness when La Nina features are dominant in the Pacific make the time frame during the first week of July very important. Late-week forecast maps show daily chances for shower and thunderstorm activity for much of the western and northern Midwest with total rainfall of more than 1.5 inches. This would be very useful moisture as corn goes further into pollination and soybeans approach the blooming and pod-setting stages. However, forecast models have a tendency to overstate the precipitation totals, so actual rainfall amounts by July 6-July 7 will garner plenty of attention.

Driving through my part of Minnesota over the weekend, it was noticeable that corn appears to be in survival mode. The telltale signs of pineapple-looking curled leaves and moisture stress were apparent. You can find more about what that means here:…

I did not recall that my area was in drought. We have had less frequent and lighter precipitation lately, but I did not remember being in drought. When I went home, I looked at the drought monitor (…), and my eyes were not deceiving me. On the latest map, released on June 23, my area had just been placed in the D0 or abnormally dry category for the first time since April 12. Abnormally dry, sure, but not in drought. Being on sandy soil, I did not give my crispy-brown grass much thought. I had chalked it up to my soil texture. But this year, my grass looks just as bad as when I moved in the same time last year when my area was flirting with D2 drought.

But given all the heat and dryness our area has been in over the last couple of weeks, it should be no surprise to me -- we are in a "flash drought."

As defined by NOAA here:…, flash drought is a "rapid onset or intensification of drought. It is set in motion by lower-than-normal rates of precipitation, accompanied by abnormally high temperatures, winds, and radiation (sunlight). Together, these changes in weather can rapidly alter the local climate."

And they are not kidding. Just a week ago, driving through the same areas on my way to run some errands, I was smiling as I drove past corn fields with rapid growth and good-looking, dark-green leaves. It was hot, breezy, and sunny, but I was happy that my part of the country was not suffering the same delayed effects of the wet spring many other parts of the Corn Belt found themselves in. I especially thought about those in the Red River Valley between North Dakota and Minnesota and wondered what fields looked like up there in comparison. But fast-forward a week, and I cannot believe how quickly the tides have turned. What first appeared to be a good thing to get some heat into the crop has quickly turned my area from one with ample moisture to one that is moisture-starved. It is looking more like 2021 in my area than what I thought it might be given the active spring pattern. But that is how flash droughts work.


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