Pacific and Indian Oceans Influences Our Weather

There are many features in the atmosphere and oceans used by forecasters to get an idea of future weather but a main driver for our winters in the Eastern US is the tropical Pacific and Indian oceans. To understand how the oceans on the other side of the world affect our weather you must first understand that the upper air pattern is not much more than a wave pattern of ridges and troughs. A trough generally is associated with cold stormy weather while ridges with warm calm weather so the locations of these ridges and troughs are important in deciding our weather conditions.

Since weather flows from west to east, activity in the Pacific and Indian oceans can initiate a wave pattern that could either produce a ridge or a trough over the eastern US. It all begins with tropical convection (intense thunderstorms) in these distant oceans which create a trough to their north which in turn forces a ridge to the trough’s east and then another ridge east of that and so on until the wave gets to the eastern US. Where this convection is located will determine how the upper air pattern is configured and where the ridges and troughs are located. Where the convection in the tropical oceans develops is strongly influenced by the water temperatures. Generally thunderstorms want to develop over the warmer waters which ties into El Nino and La Nina winters and why they are so important.

The Madden–Julian oscillation (MJO) chart below serves as a graphical representation of where the convection was located in the past and projected for the future. The thin black and red lines indicate the past and the numbers are the days of the month. The spaghetti plot with the bright green line in the middle is the forecast moving forward (concentrate on the green line which is the mean of the ensemble members which are all the yellow lines). The warm phases for the eastern US are 4,5,and 6 (representing the Maritime Continent and Western Pacific) so you can see we are going to be warm for a while. Zone 7 is a transitional phase and 8,1,and 2 (which represents convection around the dateline)are cold phases for us which may be where we are headed in February. The circle in the middle is the circle of death and indicates the MJO (or the tropical Pacific and Indian Oceans) have little impact since there is little convection at that time. The further out the line is from the center, the stronger the convection is and the more it is influencing the overall weather pattern.

As I stated this is only one parameter in a very complex atmosphere so it’s not as easy as looking at the MJO to determine weather. That being said it is an important tool to reference especially in the winter months. I hope you found this interesting.