The final June climatological outlooks from the NOAA Climate Prediction Center (CPC) issued on May 31st continue to show similar patterns as the initial outlooks from mid-May. On the temperature side, there are higher probabilities of warmer-than-average conditions across most of Iowa. A “leaning below” normal signal is also found on the precipitation side across much of the Corn Belt, including Iowa. The probability is not exceedingly high (5-10% increased chance of wet conditions). As a reminder, June is the wettest month of the year climatologically for most of Iowa. Some of the pattern behavior is also derived from unseasonable dryness through the second half of May along with already dry (and drying) top and sub-soil moisture conditions.
The recent dryness and longer term dry period back to 2020 are adding to the problem. There is limited water available in the soil profile and likely into shallower ground water. Most row crop issues are still relatively minor. Grasses and small grains could experience some stress. Hay cutting and drying has been easier with drier air and less rain. Early season disease issues may have been reduced a bit.
Looking at the potential for meteorological summer (June-July-August), CPC outlooks are not showing a clear signal for temperature, which we term as “EC” or Equal Chances of above/below/near-normal behavior. We’re also seeing a slightly elevated wet signal, which meshes with the El Niño signal that is likely to form in the early summer timeframe (and longer term trends). Initial modeling earlier this year suggested the emergence of El Niño in late summer after several months of ENSO-neutral conditions; ENSO stands for the “El Niño-Southern Oscillation” and is a multi-decadal climate driver in the Pacific Basin. El Niño (warm phase) and La Niña (cold phase) generally occur on a two to seven-year cycle. Updated ENSO probabilities in spring showed a more rapid El Niño formation in late spring and early summer, which would remain through the end of the year.
Current conditions in the Pacific Ocean show warmer than average sea surface temperatures in the eastern Pacific. The atmosphere will likely respond to these warmer ocean waters by producing thunderstorms farther east in the basin. While noting that there is not as strong of a correlation between summer weather patterns and the phase of ENSO, in years in which El Niño has been present, conditions are not as warm and not as dry as the La Niña phase. As a reminder, summer rainfall is driven primarily by thunderstorms, so larger-scale drivers are not as dominant as in the cold season when large-scale weather features drive the storm track.