Signs of (Positive) Feedback

High Heat and Humidity

Take a look at the dew point yesterday morning across the core of the corn belt. Dew point readings were in the mid or upper 70's across much of Iowa including 79 degrees near Esterville. These readings represent an unusually-high degree of low-level atmospheric moisture.

The highest U.S. dew point recorded was 88 degrees at Newton Iowa on July 14, 2010.

Dew points of 80 degrees or higher are rare. Areas immediately near the Gulf of Mexico, Gulf of California, and Atlantic Ocean waters see the highest readings as water temperatures near 80 will help support such humid dew points. Across the Midwest, a transport of humid air from the Gulf of Mexico or enhanced crop transpiration can bring the dew point close to 80 degrees.

The current unusually-high dew points are closely associated with high levels of upper soil moisture, as indicated in dark green and blue.

Summertime Heat

We are nearing the hottest time of the year across much of the nation.

Heat and Humidity

Hot summer temperatures, combined with high low-level moisture, resulted in dangerous heat index readings yesterday.

High levels of heat and humidity will persist today with heat index levels close to 100 degrees across much of the Midwest and Southeast U.S.

Summer Feedback

After such a wet spring, it might be a good time to review the development of any precipitation feedback loops.

A feedback loop is an earth-atmosphere linkage where anomalies in soil moisture tend to reinforce precipitation trends. Feedback loops are especially important in summer. A negative feedback loop can reduce agriculture yields over the Midwest. A positive feedback loop can result in both negative and/or positive impacts.

A positive feedback loop sets up after a persistent trend of surplus rainfall.

Consistently wet soils and actively-growing crops and vegetation pump moisture back into the atmosphere, thereby increasing the chance of daily rainfall. 

Rainfall has been developing along the northern edge of a ridge of high pressure centered over the South Central U.S.

Thunderstorms form along a convergence of moisture, assisted by the heat of the day and then slide southeast with the jet stream.

The unusually/record wet spring has resulted in negative impacts such as delayed planting and flooding along many rivers. However, it likely has also set the stage for a positive future impact with ample soil moisture throughout the remainder of the growing season.

Once a feedback loop is established it can take months to work out of it.

 It is likely that enough sub-soil moisture currently exists to support future adequate rainfall, crop group, and crop condition improvement well into the growing season. 

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