Content provided by Eric Snodgrass, Principal Atmospheric Scientist for Nutrien Ag Solutions.
Winter 2019-2020 is in the books and nationally, winter ranked 5th warmest and 107th wettest out of 125 years of weather records across the country. This winter will be remembered for having a strong and steady Stratospheric Polar Vortex which prevented long duration, Arctic cold air outbreaks. Here are a few of the highlights:
- California had its driest February on record which reduced California’s total wet season precipitation to approximately 50% of normal. While March has been much wetter, it has only returned snowpack in the Sierra Nevada Mountains to 60-70% of normal. Much of the rest of the snowpack in Rockies and Cascades is between 80-120% of average.
- Continuous mild weather across the south from Texas to South Carolina has allowed spring-like weather to arrive about 25 days earlier than normal. Unfortunately, most of the south, except for the Gulf Coast Region and Florida has been extremely wet averaging 10 inches of excess rain since the start of the 2020. Georgia and Alabama had their wettest February’s on record.
- The Midwest was mild and wet for most of winter and most of the region received 150% – 300% of normal precipitation. Below average snowfall was commonplace across the central and eastern corn belt as well as the Northeast US.
Figure 1. Statewide Average Temperature Ranks.
Figure 2. Statewide Average Precipitation Ranks (125-year record length). Source: https://www.ncdc.noaa.gov/temp-and-precip/us-maps
Spring 2019 is fresh on the minds of most growers due to record setting rainfall last March-June which delayed planting in some regions as much as 6 weeks and created nearly 20 million acres of Prevent Plant and over $5 billion paid out in flood insurance. Let’s compare and contrast Spring 2019 and the forecast for Spring 2020.
- Just like last year, excess soil moisture across the major watersheds (Mississippi, Missouri, and Ohio Rivers) will increase the probability of spring flooding. 2020 soil moisture anomalies are less than 2019 for most regions with the exception of parts of TN, KY, AL, MS, and GA as well as the Dakotas.
Figure 2. April5, 2020 calculated soil moisture anomalies. Source: https://www.cpc.ncep.noaa.gov/products/Soilmst_Monitoring/US/Soilmst/Soilmst.shtml
2. A big difference from last year is snow melt. March 2019 had expansive snow cover from the north central Plains states to the northern parts of the Midwest and Great Lakes States. As of mid-March 2020, only eastern North Dakota and northern Minnesota and Wisconsin had winter snowpack that still needed to melt. This will lessen the flooding potential compared to 2019.
3. Drought occupies three keys areas in early spring – California through Oregon into the Columbia Basin, the 4-corners states, and southern Texas. While this is similar to 2019 (except for California), the extent and magnitude of the drought it greater in these areas for 2020 according to the US Drought Monitor.
4. Here is a breakdown in the differences in the behavior of the atmosphere this Spring.
- Global Wind Anomalies seemed to have peaked earlier than in 2019. If they continue to calm down in April, this will allow for more blocking in the weather patterns which could reduce the frequency of low-pressures systems and rain as well as keep temperatures mild.
- The Quasi-Biennial Oscillation (QBO) is a metric to monitor winds at the base of stratosphere over the equator. The QBO in Spring 2019 was rapidly increasing too much above average values but in Spring 2020, the QBO is showing negative anomalies and is slow. This also leads to warmer and drier Springs conditions for the central US.
- Spring 2019 favored El Niño-like behavior in the central Pacific. Spring 2020 features near normal conditions in the central pacific and at times, the Trade Winds have been stronger than normal (an early symptom of La Niña).
Figure 3. April 6, 2020 global seas surface temperature anomalies (with notes). Source: https://www.tropicaltidbits.com/analysis/ocean/
Mid-April temperature patterns will force Midwest growers to wait a bit longer before getting planting corn and beans. Two large ridges are pushing into Alaska and the North Atlantic which will force a trough to develop over the Canadian Prairies to the Hudson Bay. This pattern will allow about 10-days of colder than average weather into the eastern half of the US. Overnight low temperatures have a high probability of falling below freezing for most of the corn belt through April 15 (at least) which is near the climatological last frost date of spring. If you would like to see local historical data about frost, GDDs, and corn maturity, check out the Midwest Regional Climate Center’s site.
Figure 4. April 10-15, 2020 surface air temperature anomalies forecast by the 20-member GEFS ensemble on April 6, 2020. Source: NCEP GEFS created by Snodgrass
Spring planting windows will be tight initially with saturated soils (especially near rivers), cold mid-April weather, and regular spring rains. This will slow normal corn planting progress below the 30-year average of about 7% by April 15. However, long range forecasts from the ECMWF suggest April 15 – May 15 could see drier weather. As warmer temperature rebound with longer days and better sun angles, planting windows could open up as we approach the last week of April and start May – especially for the Midwest and western corn belt. The eastern corn belt (IN, OH, MI, TN, KY) will likely continue to struggle to find long stretches of drier weather, while the south (from TX through TN and surrounding states) continues with one the wettest springs on record.
Figure 4. ECMWF forecast for precipitation and temperature anomalies for April 15 – May 15, 2020. Source: https://maps.weatherbell.com/
Summer 2020 for the Midwest is a challenge to predict this early. But here is what I am seeing.
- Long term trends for summer weather across the corn belt over the last 70 years have been getting wetter while extreme temperatures have become less common. This has helped push yields to their current highs (trend yield on corn is 181 bu/ac when 2012 is removed from the dataset).
- Forecast models are not picking up on a pattern that would suggest hot/dry weather for a large section of the corn belt. Most are forecasting the western US to be warmer and drier than normal which means the jet stream ridge may prefer a peak over Idaho and Montana rather than Minnesota and Wisconsin. If that is the case, we will have northwest flow in the jet stream which means fewer days of extreme heat and more thunderstorm activity for most of the corn belt. This would lead to a great crop year for most.
- I am concerned that the trade winds are currently stronger than normal and that ocean temperatures are cooling off the west coast. If a La Niña-like pattern develops early, then the likelihood of seeing summer heat/drought develop increases. What will most likely happen is a weak La Niña will form by fall, which will increase the probability that the 2020 hurricane season will be above average.
One last statement – long range, monthly forecasts are designed to find the general pattern of the atmosphere. They are not highly accurate and generally verify as accurate less than 50% of the time. So, we will have to watch this all unfold together!
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