When cool fronts aren’t very cool
By Skip Rigney
For those of us longing for a respite from the summer heat, today’s weather map might inspire hope. Unfortunately, looks can be deceiving.
Today’s map shows not one, but two cool fronts, headed our way. The closest stretches from Virginia into northern parts of Mississippi, Louisiana, and Texas. The second is moving southeastward out of the Great Plains.
Should we dig through our closets for hoodies and jackets? Check the antifreeze in the car? Make some hot soup? Check the calendar. It’s still August. So, no, unless you happen to like hot soup regardless of the outside temperature.
The first question regarding August cool fronts is whether they have enough push to make it all the way through south Mississippi and into the Gulf. To answer that question, forecasters look at the winds, pressures, and temperatures several miles above the earth’s surface. Currently, at an altitude of four or five miles above sea level, a warm dome of high pressure is intensifying over the western United States. Meanwhile, also at high altitudes, a trough of low pressure is developing southward from the Great Lakes toward the Gulf Coast.
Between these two features the upper level winds will increasingly blow from a north and northwest direction from Canada across the Great Plains into Texas and the western Gulf of Mexico.
That upper wind pattern is favorable for driving the surface cool fronts that are currently to our north all the way to the Gulf Coast. But, barely. Upper level winds during summer are weak compared to the other seasons of the year. Even if the fronts do move past us, they won’t go far.
The second question regarding August cool fronts is just how cool the air is behind them. A reasonable question to ask is why are they called cool fronts if they’re not cool?
Earlier in their lifetimes the fronts headed our way were at the leading edge of noticeably cooler air. Ahead of the front yesterday in Omaha, Nebraska, the high temperature was 90 degrees. The cool front passed vvthrough Omaha late yesterday afternoon. Today’s high in Omaha will be in the lower 80s.
The problem is that as that cooler air moves southward, it continues to warm up as it moves over ground that has been heating up for months. By the time a cool front gets to us in August, there’s just not much, if any, “cool” left.
But, the front is still recognizable as the leading edge of a wind shift and a decrease in humidity. So, after the fronts pass on Sunday and Monday, we can expect a light northerly breeze and a slight drop in the humidity.
But, don’t expect that wonderful dry feel to the air that we get with our first “real” cool front in the fall. These two cool fronts just aren’t that strong, and they’re not going to make it very far down into the Gulf.
The drier air will mean that showers on Sunday and Monday, if any, will be few and far between compared to the last several days. However, by mid-week the fronts, if they haven’t dissipated completely, will pull back to our north, and we will be back into higher humidity air and increased afternoon thunderstorms.