State climatologist: Nearly 15 inches of rain needed to end the drought

Image: MGN Online

Image: MGN Online

HUNTSVILLE, Ala. – Drought begets drought.

It is a saying you hear often in the midst of significant droughts, and that is because it could not be more accurate.

Crops have long dried up, yards have become barren and trees across north Alabama, known for their brilliant fall color, have simply turned brown.

The worst drought since 2007-2008 has a death grip on the Tennessee Valley and it is not letting go.

Palmer Drought Index

The Palmer Drought Index is another drought product meteorologists and climatologists use to describe the severity of ongoing droughts. The terminology sometimes differs slightly from what you see on the U.S. Drought Monitor, but the message is basically the same.

The National Center for Atmospheric Research defines the Palmer Drought Index as follows:

“The Palmer Drought Severity Index (PDSI) uses readily available temperature and precipitation data to estimate relative dryness. It is a standardized index that spans -10 (dry) to +10 (wet). It has been reasonably successful at quantifying long-term drought.”

Alabama State Climatologist Dr.  John Christy includes a link to the most recent Palmer Drought Index for Alabama on his website.

To completely end the ongoing drought, we would need between 10 and 15 inches of rain over the entire Tennessee Valley.

Will it actually rain again?

The simple answer? Of course.

It is important to understand however, that it can be very hard to get significant rain to develop during a big drought. There is no meaningful moisture in our soil or plants for the atmosphere to work with right now. We would need days of south winds off the Gulf of Mexico to bring in air with an appreciable moisture content.

We have not had this in months, which is why the last few systems that normally would produce a decent amount of rain have simply fizzled as they passed by.

A cold front moving in late Thursday may produce a few showers, but the rain will likely not be as widespread as this image suggests (Image: WHNT News 19)

A cold front moving in late Thursday may produce a few showers, but the rain will likely not be as widespread as this image suggests (Image: WHNT News 19)

There is some hope for a pattern change – albeit brief – later this week. The upper ridge that has been parked over head slides west, allowing for a trough to develop over the eastern part of the country. This will be enough for a cold front to slide through during the Thursday- Friday time frame, but the amount of rain that may accompany this system is still in question.

Forecast models are handling this system very similarly to the last few systems. They show some rain, but what ends up happening is usually a lot less. Keep that in mind when viewing any rain projections for the upcoming system. The models will generally be more optimistic than we will; we remember what happened last time Рthe models do not.