Why So Dry?
July 09, 2012 8:27 PM
We’ve finally gotten some relief from the heat and humidity, but we’re still longing for rainfall across the region. As mentioned in our previous blog, the latest drought monitors are now placing a majority of the area under abnormally dry or moderate drought conditions. Lately, a few lucky farmers may have seen a brief shower or two; but it hasn’t been enough to improve the situation. Even Friday night’s cold front that sent temperatures dropping from the 100s to the 70’s in a matter of hours wasn’t enough to get a few showers going. Fortunately, there is rain in the forecast later in the week; but even those may be isolated in nature. Until then, farmers may need to continue irrigating their crops without the help from Mother Nature.
Not only has this summer’s weather pattern yielded extreme drought conditions across the upper Midwest, but much of the country as well. The reason for this is very closely related to the extreme heat waves that have impacted our region over the past couple of weeks.
The image below shows the jet stream’s position as of noon on Monday. The positioning of this meandering river of air in the upper levels plays a huge role in forecasting heat waves and droughts. Notice how the jet stream has a well-defined ridge over the western half of the continent with a trough on the eastern half. Areas on the western edge of the ridge are characterized by rising air that would more likely lead to widespread beneficial rainfall while the eastern edge is characterized by sinking air leading to drier conditions.
Last week’s pattern was very similar to this week’s except the ridge was positioned farther to the east placing much of the upper Midwest dead in the center of the ridge. This lead to the extreme heat we saw last week along with dry conditions. With this week’s ridge positioned across much of the west, it is their turn to experience the extreme heat. Notice how temperatures across the west compare to temperatures across much of the east in the image below.
Since the upper Midwest is positioned on the extreme eastern edge of the ridge; even though temperatures may not be quite as hot as they were last week, our rain chances are about the same. Of course, there’s often a chance of isolated showers and thunderstorms during this time of year; but our chances of widespread beneficial rainfall are slim until the ridge starts to break down.
Luckily, models are hinting at the possibility of the ridge flattening out later on in the week. The question is, is the ridge too strong for that to actually happen? Even if it does, will the jet stream shift far enough south to bring us better chances of rainfall into the weekend? Be sure to stay tuned to KDLT and KDLT.com as we continue to monitor this ongoing drought.