Thursday, June 14, 2012

Drought Relief For Some Areas

Conditions were looking bleak at the beginning of May.  Only four months of above normal rainfall had occurred in the previous 28 months.  The details can be found in a previous blog post (here).  Much of the state was in a drought and the situation was getting worse.

Two events happened to change the course of the drought.  First, Tropical Depression Beryl brought much needed rain to parts of the drought-stricken Midlands.  However, there were still areas that received little rain.  This was soon followed by an upper-level pattern that brought copious amounts of rain to the Southeast, especially along parts of the central Gulf coast.  It eventually made its way to South Carolina bringing an abundance of rain.  More than 8 inches of rain fell in just four weeks in the Columbia area.  The result has been flooding of some of the creeks in the area.

Flooding of the Rocky Branch Creek closed the intersection of Main St. and Whaley St. on Monday, June 11.  Click on any of the images for a larger view.  Image Credit: USGS.

There has been a significant improvement in the drought situation as depicted by the US Drought Monitor.  About 75% of South Carolina was in the severe drought or worse as of May 1st.  However, by June 12, only about 28% of the state was in that category.  This is a substantial improvement in the past 6 weeks.  In fact a little over 16% of the state is out of drought conditions.

A comparison of the drought by the U.S. Drought Monitor.  The map on the left is for May 1, while the map on the right is for June 12.  The table below compares the two time periods.  Image Credit: USDA.

Week                   Nothing   D0-D4      D1-D4        D2-D4       D3-D4          D4
May 1, 2012           0.02       99.98       98.93         75.20         35.19         2.41
June 12, 2012       16.47      83.53       54.60         27.88          4.46          0.00

Tropical Depression Beryl brought the first surge of rain to the southeastern half of South Carolina.  The counties of Barnwell, Bamberg, and Orangeburg counties saw 4 to 7 inches of rain from Beryl.  Much of the northwestern half of South Carolina saw little rain from this system.  In fact, Beryl missed the core of the drought-stricken region, the area from Macon to Augusta, Georgia.  The past 365 days have been the driest on record at Augusta by over 3 inches, and Georgia climate division 6 (east-central GA) had its driest 24-months on record, nearly 26 inches below normal.

Tropical Depression Beryl at 9:15 a.m. edt on May 29, 2012.  Image Credit: NOAA Environmental Visualization Lab.

The next surge of moisture began moving out of the Gulf of Mexico late last week.  An upper-level disturbance was slowly moving through the Southeast.  This brought two waves of rain through the Midlands Sunday and Monday.  The two day totals were generally between 1 to 2.5 inches of rain.  This put a damper on the NCAA Super-regional baseball tournament being played in Columbia.  It brought much needed rain to Augusta, Georgia where 2 to 5.4 inches of rain fell across the city.

The weather pattern at 500 mb shows a weak upper-level disturbance over the lower Mississippi River Valley at 00z on June 11, 2012.  Image Credit: WSI.

The precipitation analysis from the Advanced Hydrologic Prediction Service shows that a large area of South Carolina has seen much above normal rainfall over the past 30 days (May 12 – June 12).  Parts of Barnwell, Orangeburg, and Williamsburg counties have been as much as 8 inches above normal.

Rainfall anomaly for the 30-day period ending June 12.  Click on the image for a larger view.  Image Credit: NOAA\AHPS.

Why isn’t the drought completely over?  It takes a long time to get into a drought and droughts are rarely over in a short time.  However, if the weather pattern is changing then this could be good news for parts of the Southeast.  This is the wettest time of the year for the Midlands.  An average or above average summer rainfall should alleviate the drought by fall.  Keep in mind that El Nino may be back by the fall and this would likely bring wet conditions for the winter.