The final February climatological outlooks from the Climate Prediction Center (CPC) show a strong signal for colder than average temperatures across much of the upper Midwest, including Iowa. On the precipitation front, there is an elevated probability for wetter than normal conditions. December, January and February are the driest three months for Iowa, so when looking at probabilities, it doesn’t take a lot of moisture (or lack thereof) to be above or below normal. Another interesting observation is that these outlooks show an expansion of the classic signals that are typical for a moderate La Niña. La Niña is forecasted to persist into early spring with a slightly better than 50% chance of transitioning into a neutral phase of El Nino-Southern Oscillation (ENSO) during late spring and early summer. Seasonal composites of rainfall behavior into summer show that if La Niña is present, drier conditions could prevail across portions of the Midwest.
Current conditions
The current Arctic air outbreak is a result of the destabilization of the Polar Vortex. The Polar Vortex is a large low pressure system over the Arctic basin that dams off frigid air from the mid-latitudes. When the vortex weakens and begins to wobble, meanders form that allow bulges of cold air to intrude into the Midwest. The short-term CPC outlooks have been hinting at this behavior over the last week and the most recent iterations suggest that we will be in a cold snap (or at least unseasonably cold) into the middle of February. With the jet stream dipping farther south, a less active storm track is anticipated, as reflected in the current short-term precipitation outlooks.
Soil conditions
Much of western Iowa entered winter with much drier than average soil conditions. With mostly frozen soils, even the decent snowpack will not improve soil moisture conditions. The main opportunity to improve soil moisture before planting is to have some rains after the soil thaws and before planting. There will likely be some rain to improve conditions. But much of western Iowa is quite likely to go in to planting with very dry soils.
Thus, most crops in this area will be reliant on ongoing/regular precipitation and need limited dry periods to avoid crop stress. The dry soils should allow for earlier field access and should encourage deeper root development. Some increased risk of stress for crops is likely going to carry into the growing season.
Early spring outlook
The initial seasonal outlooks for February-March-April continue to show a temperature and precipitation signal in line with La Niña -- colder than average conditions over the Pacific Northwest and higher probabilities of wetter conditions across the Ohio Valley; these elevated probabilities bleed into extreme eastern Iowa along with a good chance of warmer than average temperatures for the entire state. Longer-range products into the growing season show that warmer and wetter conditions may reign across the state, though the next iterations of the seasonal outlooks will be highly dependent on multiple factors, including snowpack, soil moisture, whether there is a transition in the ENSO phase, etc. … so stay tuned!