As we start the new month of November, it’s interesting to see how our daily weather impacted the overall weather for October. A variable called stream function best conveys the necessary aspects of our October weather. Stream function can be easiest understood if it is thought of as a water hose where the water moving through the hose is the wind. The first way this example works is that if a narrower passage way for the water occurs in the hose like if a finger was put on the end of the hose to close down some of the opening‘s space, then the water has to move faster through it. Consider the faster movement as the jet stream. Another way this example works is if you were to consider that a normal stream function or hose is straight horizontally. Therefore, a stream function departure from normal or anomaly is when the hose is curved or circular. In the interest of keeping this simple, just consider these curved or circular departures from normal as high or low pressure systems. These concepts will be utilized below. For our analysis, the latest data goes through the 29th of October so the strong wind and rain storms along the Gulf Coast to end the month of October will be left out.
With all of that in mind, the October analysis shows many areas that impacted our weather. One can see the connection to the tropics along the Southeast United States that provided the record rainfall in accordance with Joaquin’s formation and subsequent stream of moisture into the United States even as the storm stayed offshore. This also shows up in the precipitation departure from normal with an greater than normal moisture in the South Carolina and Georgia. Another area of low pressure also shows up near the Baja Peninsula. This is most likely the result of multiple upper level troughs of low pressure passing through the area as well as the passage of strong Hurricane Patricia off the Baja Peninsula coast. Remember, the remnants of quickly dying storm Patricia moved into Mexico south of the Baja Peninsula and crossed into the Gulf of Mexico and then into the United States bringing damaging winds and a strong stream of moisture inland. Above normal precipitation also shows up in the precipitation anomalies plot as a result of that along the south coast of the United States. Furthermore, the main jet stream location during the month of October shows up in the stream function anomalies plot in between high and low anomalies located close to each other. The jet moves in from Alaska southeastward into the United States and can be recognized as the polar jet stream. This kind of jet placement often results in warm air being able to reside in the West, which shows up nicely in the temperature anomaly plot. Also in the temperature anomaly plot, cooler air shows up in the Northeast and Eastern Canada. This resembles the cooler air that was able to move into the northern and eastern portions of the United States around the 17th to 19th of October. The jet stream placement and warm air actually resembles how the weather pattern often looks like in the winter time with El Nino as the main driver of the weather pattern. As previously mentioned, it must be recognized that the rainfall to end October is not included in the pattern plot, but it is interesting that the anomalous flooding rainfall that occurred as a result of the landfall of Patricia’s remnants do not show up in the precipitation anomalies plot over Northeast Texas. In fact there is a negative precipitation anomaly there. Most of the rest of the United States received negative precipitation anomalies, but it is interesting to see the above normal precipitation in the Southwestern United States because the Southwestern Monsoon is the main cause, aside from tropical connections, of precipitation in that area during the summer months.