Hot one Day...Cold the Next
by Angela Schilling, Meteorologist
September 11, 2011 9:20 PM
September has proved to be a weather roller coaster of a month, with both heat waves and cool downs. Monday, September 12th will be the hottest day of the week along the I-29 corridor with 90 degrees certainly attainable. As we look long term, temperatures will plummet as we head into the middle portion of the week. Oftentimes forecasters will use teleconnections to predict the weather several days out.
In a nutshell, teleconnections takes a look at the current set up around the world and uses those observations to make forecasts long term. One of the most common or most well known teleconnections is the Southern Oscillation index. An El Nino pattern is associated with a negative SOI and a La Nina pattern is positive. A La Nina pattern is typically associated with a more amplified jetstream aloft, which is what drives the weather. You can think of a trough/ridge pattern as a more amplified set up. Typically the Atlantic Basin (Gulf of Mexico/eastern seaboard) sees an increase in tropical activity with La Nina. Currently, the SOI is positive, and is expected to strengthen over the upcoming months.
An interesting Teleconnection is the relationship between eastern Asia and the eastern seaboard of the United States. Lets say there is a ridge of high pressure over New England and a typhoon over Eastern Asia…now you can expect a trough of low pressure over the eastern seaboard 6-10 days later. At the time being there are several areas of low pressure over Eastern Asia…and a ridge of high pressure just off the east coast of the United States…which means a trough of low pressure may move into the northeast over the next week or so.
How will this affect us? Since we’re located just to the west of say North Carolina or Massachusetts, we may see a trough of low pressure develop over the next several days. As a matter of fact, a cold pocket of air is expected to dig southward into the Northern Plains by Tuesday afternoon.
East Coast...Friday afternoonNorthern Plains...Tuesday Afternoon
In the mean time Monday will be the hottest day of the month so far, with many areas in the southeast approaching, if not topping 90 degrees. Highs on Sunday, September 11th, were in the mid 80’s west of the James, and low 90’s along the Missouri River. The record for September 12th is 97 degrees in Sioux Falls, set back in 1908. Unlike June or July, dewpoints are very low right now into the 50’s, keeping heat indicies at a minimum. High winds will also provide a little bit of relief from the heat on Monday. Winds are expected to be around 15 to 25 miles per hour, coming out of the south in advance of our next cold front. A reinforcing shot of cold air is expected to build into the region on Tuesday dropping temperatures significantly…stay tuned to KDLT and KDLT.com for further updates.