The pattern across the eastern half of the United States is very conducive to flooding. A high pressure located near Bermuda, called a Bermuda high, helps to direct warm and moist flow from the Gulf of Mexico northward into the United States while in the northern portion of the United States is from west to east dragging a few energetic disturbances towards the eastern United States.
Furthermore, flow in the northern mid-latitudes has slowed down allowing the Bermuda high and cold front across the Midwest and Northeast to remain stationary. The low level jet stream running along or just ahead of the cold front continues to draw tropical moisture north into the northern United States so that many areas across the Mississippi and Ohio Valleys have a flash flood watch on Saturday and Sunday. As this pattern remains stationary, disturbances moving through will allow for plenty of showers and thunderstorms. While considerable cloud cover will lower the threat of intense thunderstorms, which need plenty of energy from the sun, heavy rain, and therefore flooding, is very possible with high and near or exceeding record values of precipitable water. (Precipitable water is a measure of the amount of moisture in the atmosphere if all the water were precipitated as rain.) With this in mind, excessive rainfall is forecast along the front over the next three days. In addition, an upper level low pressure moving slowly north from the Gulf of Mexico will add to the rainfall totals making flooding likely. In this pattern, convective rainfall or rain caused by thunderstorms won’t mean that rain will be constant, more off and on. With the front slowly moving southeast, the off and on rainfall should continue in most places until the end of next week.
Meanwhile, drought has continued to increase across the United States, especially in western New York and eastern New England. While the final location of both the front and upper level energy is key to the exact placement of high precipitation amounts, the rainfall from this week’s rainfall should help to eat into the drought in areas like the Great Lakes and western New York. If the front is further east, then there would be a possibility that eastern New England would get into the higher totals. To lessen the drought, the longer drawn out precipitation is what those regions need more than quick events with high amounts of precipitation because the rainfall needs to soak into the ground and remain in the ground for longer periods of time. So since the rainfall should be the off and on variety, to eat into the drought, one would hope that the rainfall would be many small to moderate amounts rather than a many small amounts and one large amount of rain.