When you picture a summer day in the Southeast, the first thing that comes to mind is the “stickiness” or high humidity of the air. Usually, hot summer days are actually associated with higher dew points here when winds blow from the Gulf of Mexico or the tropical Atlantic.
That is not the case with the Southeast regions today.
Using the map above, you can see that although dew points above the 60s and 70s persist, especially west of the Appalachians, the areas east of the mountains appear somewhat dry. unusual way.
Why does this happen?
Downhill occurs when air is forced to descend from higher altitudes – in this case the peaks of the Appalachians. As the air descends, it warms and dries, thus resulting in higher temperatures and lower dew points.
While this effect is often more pronounced in more mountainous areas – such as the West Coast – it can also occur in the Appalachians.
If you refer back to the steam loop, you’ll note that the flow around the crater allows air to move in from the NNW. This air is going up the Appalachians in the west and then down in the east. The Appalachians are oriented from southwest to northeast, allowing them to take advantage of this current and produce some pretty dramatic dry winds.
Dry air is easier to heat than humid air, as I mentioned before. Although not particularly obvious, regional maximums are perceivable in the only downwind regions of the Appalachians. Drier air can make the difference between high temperatures below 100 or just over 100.
Keep in mind that the Appalachians are not nearly as tall as the Rockies or the Cascades. Air has a shorter slope to move downwards, resulting in less severe heating/drying. However, it is still happening clearly today because the dew point decrease is visible through the observations.
If you’re at GA Center today and you’re a few degrees hotter than your friends at AL Center, now you know why!
** Special thanks to my classmate, Tim Ealer, who inspired this blog through our forecast discussion today.