Ridging has continued to build over the southeastern quadrant of the United States over the last few days, which has been responsible for a large region of anomalously hot temperatures and drier air. This ridge is currently centered over eastern Arkansas and western Tennessee but will begin to split as a mid-to-upper level closed low moves from the eastern Gulf of Mexico and into the Southeast early next week. Given that ridging is associated with sinking air which often limits storm development, the splitting of this ridge will result in a drastic change in sensible weather conditions in the coming days.
The National Hurricane Center has outlined a disturbance in the eastern Gulf of Mexico and is giving it a 40% of tropical or subtropical development over the next 5 days. Even though the Atlantic hurricane season doesn’t technically begin until June 1, it wouldn’t be a big surprise to see a weak subtropical/tropical disturbance develop, if convection (thunderstorm development) can consolidate over a small enough region in the Gulf. The upper-level trough/closed low (the feature that is splitting the ridge over the Southeast) will continue interacting with a region of broad surface low pressure moving into the Gulf, which should assist in its further development since the upper-level dynamics will be supportive. Whether or not we get our first named system out of this is not necessarily important from a sensible weather standpoint. The impacts will be about the same regardless, which is what the primary focus should be on.
Let’s talk about potential impacts and how the weather should change compared to last week/this weekend. The mid-south (Louisiana, Arkansas, most of Mississippi, most of the Southern Plains, and areas just northward) will remain quite toasty for a large part of the week since the closed low and developing surface low should remain to the east/southeast of those regions. However, farther east, temperatures should be cooler due to enhanced rainfall for most of the week, but the transport of deeper moisture into the area will result in muggy conditions, making temperatures feel warmer. Instead of trying to put all of this into words, take a look at the map from the Weather Prediction Center (NOAA) that shows the projected rainfall totals over the next 5 days. Don’t focus as much on exact amounts, but take note if you’re located in a region that is expected to get more than a couple of inches of rain (purplish/reddish-shaded regions).
The big impact will be the heavy rainfall, although that’s not necessarily a bad thing since many areas have recently been dry. However, be wary if flash flooding begins to occur and do not attempt to drive over any flooded roadways. As the rainfall map indicates, heaviest rainfall totals over the next several days should occur from Florida through Georgia, parts of Alabama, the Carolinas, and up the East Coast. Another zone to keep an eye on will be from the Ohio Valley into the Mid-Atlantic, where a frontal boundary will remain stalled out over the region. Given that this region is located along the periphery of the current ridge, winds have been westerly/northwesterly through a deep layer of the atmosphere, and disturbances will continue to be embedded within the westerlies, so storminess may be a bit more intermittent and hit-or-miss across that area. Also, this is where the severe weather threat (mainly a damaging wind threat) will be concentrated this week, along with a severe weather threat across parts of the Great Plains. Firsthand Weather will address those risks on a day-to-day basis. Partially due to the moistening of the environment through a deep layer farther south across the Southeast, this should mostly limit the severe weather risk, since temperatures will not decrease with height as rapidly (resulting in lower instability). We’ll still keep an eye on it just in case though.
To briefly summarize, expect a change in weather conditions across a large region. Many will be transitioning from a dry and hot pattern to a warm, muggy, and wet pattern. Given the position of the large ridge, the low in the Gulf of Mexico will not be in a hurry to move out and will have to be swept out by an incoming trough later in the week. In the meantime, get used to the wet (or at the least, muggy) weather!