Today is my last day as Hydrologist in Charge of the National Weather Service’s Southeast River Forecast Center, as I plan to retire.

I have enjoyed communicating interesting aspects of weather, water, and climate across the Southeast U.S. over the past few years. It seems like there is always something going on that is worth communicating. I have discussed aspects of major floods, hurricanes, and, more recently, drought.

I’d like to thank Nene Robertson, my assistant, who served as my top-notch reviewer.
I’d like to thank Jeff Dobur (Water Resources Manager), Todd Hamill (SCH), John Schmidt (DOH), and Jack Bushong (HAS forecaster) for their frequent input.
I’d like to thank the entire SERFC staff where I obtained ideas for Journal content.

Finally, I want to thank you for being a loyal reader of the SERFC Journal.

The SERFC will continue to provide information through the Water Resources Outlook, SERFC Alerts, and on Facebook.

In retirement, I hope to continue to communicate items of interest relating to weather, water, or climate in some way or the other.

If you have been a frequent reader of the Journal, I’d like to hear from you – and what you found useful. Send your comments to johnfeldt@yahoo.com

I thought that I would take a look at a couple of USGS gage sites. The first two, sites A and B, are smaller tributaries within the Savannah River drainage. Site C is on the Flint River within the core of long-term drought.

Here is a summary of the past 30-day percent of normal rainfall. Sites A and B are within the area that experienced above-normal rainfall, as indicated in blue. Site C was within the area of persistent below-normal rainfall.

Let’s take a look at the USGS hydrograph for Site A. First, note that all flows are 300 cfs or less – which represents extremely little water in respect to the Savannah River. You can see a slight bump in the flow, likely due to a passing thunderstorm. Unfortunately, the duration of this enhanced flow is very brief before it returns to hardly any flow at all.

We see a similar situation at site B in North Georgia. You can see the occasional bumps in flow due to passing storms. Again, after the rain ends, flows quickly return to very low levels.

Thus, while the recent trend of afternoon showers and storms might have helped moisten upper soils, for the most part, it did not result in a significant increase in runoff into area rivers or lakes.

In fact, flows remain near historic low levels within the core of the drought. Along parts of the Flint River, flows continue to run within the lowest 10 percentile. In this duration hydrograph, the arrow points to the current reading. Note how flows have persistently remained within the lowest 10 percentile (the brown-shaded region).

IRI uses a number of inputs for their forecasts, primarily several dynamical atmospheric prediction models that respond to the expected patterns in sea surface temperature (SST).

IRI is calling for normal late summer/early fall precipitation for most of the Southeast U.S. except for Mississippi, Alabama, and Northwest Florida where above-normal precipitation is forecast.

Above-normal temperatures are expected over the entire Southeast U.S.
Unfortunately, it looks like well-above-normal temperatures will continue to be centered over the Midwest.

The map contrasts plant health in the central United States between June 25 and July 10, 2012, against the average conditions between 2002 and 2012. Brown areas show where plant growth was less vigorous than normal; cream colors depict normal levels of growth; and green indicates abnormally lush vegetation. Data was not available in the gray areas due to snow or cloud cover. The image is based on the Normalized Difference Vegetation Index (NDVI), a measure of how much plant leaves absorb visible light and reflect infrared light. Drought-stressed vegetation reflects more visible light and less infrared than healthy vegetation.
Source: NASA

While each day’s recharge is incremental, the cumulative impact over many days can be significant. Another benefit of the increase in total atmospheric moisture content is an increase in cloud cover which will tend to hold down temperatures and reduce evapotranspiration a bit.

The first image I want to show is the departure from normal of rainfall over the past 7 days. Areas in grey, green, or blue indicate rainfall that is avering above normal. A majority of the Southeast U.S. has experienced normal or above-normal amounts of rainfall over the past week.

Another way to look at the situation is through the maximum number of consecutive days without rainfall (past 7 days). Most of the region has only experienced only 0 to 2 days without at least some rainfall.

The pattern of daily scattered rainfall will persist through at least the weekend. In fact, coverage could become a bit more widespread over the weekend as a weak front drops south and enhances lift over the region.

Residual moisture will persist over the region much of the week. Initially, the jet stream will remain anchored well to our north. However, by the end of the week, there will be a slight dip in the pattern with the jet stream sagging south into North Carolina.

There are several factors coming together this week that will continue the pattern of daily showers and storms.

Residual moisture is in place. Showers and storms will form during the late afternoon and evening hours coinciding with the peak heat of the day.

In addition, as the jet sags south, a cold front will also move into the region. While this front is quite weak, it will be enough to enhance the daily chances of rain later this week and into the weekend.

While this is certainly a typical July pattern for the Southeast U.S., it has not been typical at all the past few years.

This image depicts the cumulative potential rainfall amounts for the next week. Note the enhanced axis of rainfall, white dashed line, where rainfall of 2 inches or more is possible over the next 7 days.

While coverage might be scattered at any given time, the cumulative coverage over the past week has been significant, and generally quite welcome.

Here is a summary of rainfall over the past week. I’d focus on the areas of green or yellow. These areas received at least an inch of rainfall. Most of North and South Carolina, as well as Virginia, received 1 to 3 inches of rain. Coverage was a bit more scattered in Alabama and Georgia, with heaviest amounts over northern sections.

Now — back to the drought. The U.S. Department of Agriculture has declared natural disaster areas in more than 1,000 counties and 26 drought-stricken states, making it the largest natural disaster in America ever. The areas shaded in red are the disaster-declared counties.

If we take a close-in look at rainfall for a few locations from May 1 – July 8, we can see several interesting trends. I have highlighted significant rainfall (0.50 inches or more) with a yellow dot and high amounts (1.0 inch or more) with a red dot. Note the complete absence of significant rain events (generally) from the middle of June up through just recently. I have also overplayed the U.S. Drought Monitor which points out that much of the Southeast U.S. is in some degree of drought. The dry spell, with a reduced frequency of significant rain events, led towards the droughts continuation or expansion.

We can see a similar trend at Birmingham; however the situation is different in Florida. Take a look at the magnitude of rain events at Gainesville. While rain events have been spaced out, the more significant events have produced between 2 and 6 inches of rainfall.

Let’s take another look at Atlanta, this time with temperature overlaid. The orange line is temperature. Note how temperatures have climbed significantly during the recent dry spell. While some of this might be attributed to normal seasonal warming, I think more is due to very dry soils and dry air which resulted in a lack of cloud cover.

Talk about hot temperatures – according to NOAA data, the average temperature for the contiguous U.S. during June was 71.2°F, which is 2.0°F above the 20th century average. The June temperatures contributed to a record-warm first half of the year and the warmest 12-month period the nation has experienced since recordkeeping began in 1895. Scorching temperatures during the second half of the month led many cities to set all-time temperature records

The promising news is that there are signs that rainfall frequency will return closer to normal during the month of July.

Repeated occurrences of showers and thunderstorms are likely near this frontal boundary. I’ve indicated in green the area most likely to receive significant rain over the next 5 days.

Thunderstorms will be most likely when lift is enhanced. This will tend to occur when an area of low pressure moves along the front as well as during times of peak afternoon and evening heating.

Rainfall amounts will also be enhanced over higher elevations of the western Carolinas and Virginia.

I’ll provide additional updates on this area throughout the week as rainfall could be prolonged due to “training” of individual thunderstorms as well as a continued feeding of deep-seeded moisture.

South of the front, including central and southern Alabama and Georgia rainfall will be much more scattered in coverage and tied to late day and early evening heating.