Why such a dry September?

There was very little rain that occurred within the month of September. Scalia Lab only received 0.26 inches of rain for the entire month. The average for Athens is 3.15 inches and the deficit for September was -2.89 inches. The month of August was also drier than normal with a total of 1.77 inches received, a -2.61 inches below the average of 4.38 inches. This makes the total deficit for two months -5.5 inches for 2008.

The majority of weather within September 2008 was sunny and warm. The average temperature was 80.6° F for the month, 4° F above the average of 76.6° F. The average solar for Athens was 923.33 WM² and the max solar for one day was 1350 WM². An overcast day in September is around 770 WM² which means over 25 days were completely sunny within the month of September and you can’t have rain without clouds.

Are we in a drought? According to the U.S. Drought Monitor the current drought intensity for Athens County is at a D0. D0 means that the area is abnormally dry and not yet in a drought situation. At the end of September last year most of Athens was in the D1, or moderate drought, and southern parts of the county were in D2, or severe drought. The drought monitor considers the precipitation from the current year and reflects them to previous years and the effects on agriculture and hydrology. The abundance of rain earlier this year has helped to keep us out of serious drought thus far this year. However, with such low precipitation the last two months, this could be the beginning of a decent dry period.

With the total deficit in just two months being -5.5 inches, where has all our rain gone? The main source for late August and September rain is tropical system leftovers from the Atlantic and Gulf. This year only two hurricane leftovers made their way over the Southeast Ohio area in the 30 day period. The first was Gustav which produced only produced 0.19 inches in Athens on the 9th. It then produced another 0.05 inches after it developed into a low pressure system off the New England coast and brought some troughs along its southwest side the 11th and 12th. Gustav alone gave us 92% of our precipitation. The second hurricane was Ike that ended up going to the northwest of Southeast Ohio giving us strong winds that gusted to 46 mph and clouds thanks to a strong high pressure off the Atlantic coast that kept the enviroment dry.

Looking at this graph comparing the Yearly September Rainfall for the last ten years compared to the Average, the correlation between tropical storms can be seen:

For each spike the following tropical systems effected the region:
2000: Gordon
2002: Isidore
2003: Isabel
2004: Frances, Ivan (year of the big Marietta, OH flood)
2006: Ernesto
These storms all occurred in the month of September. These and other years had tropical systems that affected the area except were different months. A majority of these systems stay over the Southeast Ohio area for only a day or two. These abundant rainfall amounts come within a 24 hour period and move on speedily. This graph represents the amount of rain days in a month along with the total amount of rain that month:


Strong high pressures ruled the Southeast Ohio skies through much of September. The jet stream set up over Canada for much of the month that prevented storm systems from entering the Ohio Valley. Instead a fairly calm and tranquil period lasted from the 16th to the 25th with pressures averaging 1020 millibars. This took any system that tried to develop and weakened it before it ever reached the area and prevented much tropical storm development. Only a few fronts still remained somewhat intact towards the end of September and brought a few chances for rain as the large ridge of high pressure began to erode.

As of October 8, 2008 we finally have a small trough that has survived and run out the strong ridge in the jet stream over us. We finally got rain, over 0.50 inches actually, double what we had all last month! However current models have the jet stream once again going to our north as a strong ridge builds in.

A very strong trough digging in the west will try to move our way by the middle of next week. However, it will not be very successful as the ridge will stay in place. It appears that the next big rain-maker system maybe over a week away, most likely around the 16th of October that will also bring more seasonable temperatures. It appears October will be another dry month.



Christopher Redmond
cr898005@ohio.edu