The Old DC Split On 9 News Now at 5 PM Thursday evening I referred to a term called 'the Old DC split'. If you have lived here long enough you may be familiar with the term. Our bout with a little snow and ice late Thursday night and Friday was result of not one but two ill-defined storms or pieces of energy. I mentioned that the northern piece was trying to pull out to the north of us while the southern moisture was trying to dive south of us. When we end up in the middle, missing the bulk of the precipitation to the north and to the south, that's the old DC split. Contrary to some emails and phone calls we receive it is not the government controlling the weather patterns nor is it connected to the landing or launch of the space shuttle. We get caught up in a split flow. The northern branch of the jet stream takes one piece of energy to our north and southern branch of the jet stream keeps the other piece of energy or area of moisture to our south. We end up in the doldrums so to speak. The jet streams are fast moving currents of air that guide the track of low pressure systems and steer areas of moisture. There is always more than one jet stream and in that case we look at the jet stream maxima to help determine the path of a storm. In winter there are often two separate jet streams: the northern branch and the southern or subtropical branch. We concern ourselves with the jet streams that are about 18,000' in the air but these currents of air could be found at many levels. We can get some big snows when the northern branch of the jet stream or polar jet delivers cold air and the sub-tropical jet brings us tons of moisture. Once in awhile the two jets merge making a very intense storm and in the case of the March 1993 storm an historical storm.  ¶ 5:08 PM