Months with weather conditions warmer and drier than average are taking their toll on soil moisture in portions of the East and the South, indicating that a long-term drought could be in the making, but most likely in localized areas.
Amy Aaronson discusses the dry situation in parts of the East in this video.
A persistent ridge of high pressure, extending well inland over the eastern and interior southern areas of the nation shoved the storm track well to the north much earlier than usual this year.
During the summer months, most of the nation relies on sun-driven showers and thunderstorms for significant rainfall, while frontal systems do still play a reduced role in northern areas compared to other times of the year.
As we have seen with the downpours in recent days, in the mid-Atlantic and the South, the widespread heat and low humidity during the week of July 4 was probably just a short-term drought issue for most places, according to Southern Weather Expert Meteorologist Dan Kottlowski.
"It is not unusual for short-term drought areas to randomly show up and then break down during the summer," Kottlowski said. "However, at the local level, there can be places that have a rough time with drought this summer, because of ongoing warmer-than-average temperatures," he added.
Portions of the eastern and southern United States have had one of their warmest springs on record. Temperature departures in many locations ranged from 1 to as much as 8 degrees above normal over the three-month period from March, April and May:
The above-average temperatures have persisted in much of the same area during June and the first half of July. In some cases the departures were even more extreme:
In many locations of the East and the South, the warmer-than-average temperatures have coincided with below-average rainfall. It is only because the rainfall departures have not been huge for most areas, that we do not have more widespread and more severe drought problems right now.
During the spring and the first part of the summer, higher temperatures and increasing sun angle result in greater soil moisture loss.
According to Expert Senior Meteorologist Joseph Sobel Ph.D., about one-quarter of an inch of water will evaporate from a pan of water on a hot, sunny day with low humidity.
Not only does this mean your bird bath may run dry and your pool will need to be topped off periodically, but your vegetable garden may need a good soaking. Drought-stressed plants will not produce the yield as well as well-watered plants.
The amount of evaporation of bare soil is about 70 percent of that quarter-inch value during similar conditions. However, a sandy soil will allow higher evaporation rates compared to that of a heavy clay soil. Most lawns, gardens and agricultural areas fall in the middle of this soil spectrum.
Vegetation also pulls water from the ground via root systems, while foliage allows that water to evaporate into the air. This process is called transpiration and can deplete moisture from much deeper in the soil.
So even though a barrage of thunderstorms can unload an inch or two of rain during a summer evening, in a matter of several days the topsoil can be fairly well zapped of moisture again.
A couple of weeks without significant rain during June and July can lead to moderate short-term drought problems. Longer periods of little or no rain can begin to significantly affect ground water table and the levels of streams, lakes and reservoirs.
This is a critical time for various types of food and feed crops across the nation. Fortunately, where much of these crops are grown over the Plains, Midwest, California and Florida, there has been sufficient rain thus far or irrigation is routine.
Interestingly, the same pattern that promotes hot, less rainy conditions during the spring and early summer can contribute to a very active tropical storm/hurricane season in the South and along the East Coast.
AccuWeather.com Hurricane Expert Joe Bastardi is expecting a bumper crop of named systems in the western Atlantic this season. Joe accurately predicted the record heat for early July in the East and expects the extreme warmth to continue.
Only if these anticipated tropical rains do not come toward the end of summer season and during the fall would areas potentially run into big problems with water for drinking and recreation purposes.
We now have a "dirtier" atmosphere over many of the areas that were dry for an extended period. A flow of tropical moisture and high humidity levels should lead to better chances for random pop-up showers and thunderstorms in the East and South into the first part of next week.
However, another broad zone of high pressure could turn up the heat and shut off the storms again later next week, perhaps allowing more areas get dry for a time. The heat and drought could stress crops in localized areas that have not had problems just yet, especially over the Midwest, where the heat will be a major player in the near future.
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