Columbia's Extreme Rain Event

A complex of heavy thunderstorms formed over the Columbia, SC area last Sunday, July 21, 2012.  The heavy rains resulted in what is known as an extreme rain event.  That means that rainfall for the day had to equal or exceed 2.52 inches to be in the top 1% (99^th percentile) based on the current climate statistics.  The official total at the National Weather Service Forecast Office was 2.55 inches, thus an extreme rainfall day.

The slow moving thunderstorms unleashed a torrent of rain producing two to five inches of rain in a couple of hours.  The highest rainfall totals stretched from Lexington to Forest Acres on the east side of Columbia.  Reports of 4.89 inches came in from west of Lexington, 4.56 inches from West Columbia, and 3.48 inches from Forest Acres.

As one can imagine with all of the rain this summer the heavy rains led to flooding.  All of the usual spots flooded, but there were areas not prone to seeing so much water.  Flooding was reported in parts of Forest Acres.  Rain was so heavy in West Columbia that motorists on I-26 had to slow down and pull over in some cases.

A graph of the water levels for Rocky Branch Creek for July 17-24, 2013.  Note that a previous flood occurred on the 17th with bigger flood on the 24th.  Click on the image for a larger view.  Image Credit: USGS.

  

Water rushed into Rocky Branch Creek that flows through the Five Points Area.  By the time it reached Whaley Street it was the third highest flood on record.  The water level reached 11.46 feet, whereas flood stage is at 7.2 feet.  Roads were closed and cars were flooded.

From One Extreme To Another

June was a month of extremes across the U.S. Record heat dominated the West, where all time record June temperatures were being set in multiple states. Meanwhile, the same weather pattern that supported the prolonged, intense heat across the West locked in an extremely wet set up across the East. Not only were numerous daily rainfall records set, but both Philadelphia, PA and Macon, GA, ended up with their wettest June ever.

Some of the extreme weather across the U.S. in June 2013.  Click on image for a larger view. Image Credit: Climate Central.

You can also add Augusta, GA, to the wettest June on record.  Bush Field in Augusta received 10.83 inches of rain which was 6.11 inches above normal. An observer near Martinez, northwest of August, received 16.02 inches for June.  This is remarkable since that area of Georgia and South Carolina had been suffering from nearly 3 years of drought until recently.

2013 Hurricane Season: Very Active?

It has been a little over a month since the last of the 2013 hurricane season forecasts were made.  All of the forecasts call for an active season with the possibility of a very active season.  The third named storm of the season (Chantal) formed late on July 6, which is just over a month earlier than when the average “C” storm forms.  Is this a sign of a very active season?  Given conditions in the tropics I would say, yes.

Tropical Storm Chantal moves into the eastern Caribbean Sea.  Click on image for a larger view.  Credit: NOAA.

Two storms have already formed in the deep tropics (Barry, Chantal) and one is a Cape Verde storm which usually doesn’t get going until mid-August.  As Jeff Masters points out on his blog:

"Most years do not have named storm formations in June and July in the tropical Atlantic (south of 23.5°N); however, if tropical formations do occur, it indicates that a very active hurricane season is likely. For example, the seven years with the most named storm days in the deep tropics in June and July (since 1949) are 1966, 1969, 1995, 1996, 1998, 2005, and 2008. All seven of these seasons were very active. When storms form in the deep tropics in the early part of the hurricane season, it indicates that conditions are already very favorable for TC development. In general, the start of the hurricane season is restricted by thermodynamics (warm SSTs, unstable lapse rates), and therefore deep tropical activity early in the hurricane season implies that the thermodynamics are already quite favorable for tropical cyclone (TC) development."

This quote is attributed to Colorado State University researchers Phil Klotzbach and Bill Gray.

From Wet To Steamy

Drought has been the rule since the fall of 2009 in parts of South Carolina.  Only 6 out of the next 36 months saw above normal rainfall in Columbia, South Carolina until 2013.  Then the pattern changed and 2013 has been wetter than normal.  In fact, 4 out of the last 6 months have been above normal and July is likely to add to that total.

The first week of July has been extremely wet. The airport has seen 2.19 inches of rain while the city has received 4.35 inches of rain in just six days.  July is normally the wettest month of the year, but this year has been wetter than normal.  In fact, the last two weeks have been quite wet.

The map below shows the observed rainfall across South Carolina for the past two weeks ending on July 6.  Note that the area east of a line from Lancaster to Columbia to Barnwell has seen the greatest rain with 10 to 15 inches of rain in eastern Orangeburg and southeastern Clarendon counties.  The rain has been less west of the line until you get into the upstate of South Carolina.

The 14-day observed rainfall ending at 8 a.m. July 6, 2013.  Click on image for a larger view.  Image Credit: NOAA/AHPS.

Heavy rainfall has resulted in significant rises in many of the rivers with minor flooding of the Congaree River in the Columbia area.  The Congaree Swamp has seen considerable flooding over the past month closing some of the trails.  This is likely to continue as much of the flood waters from the Upstate have yet to pass through the Midlands.

So, why is this happening?  It turns out that our weather is linked to a pattern which has caused record heat in the Southwest and cooler than normal conditions in the Midwest.