The signs are growing that there could be a significant heat wave across the South, Southeast and Mid-Atlantic next week, with tropical humidity and highs 10 to 20 degrees Fahrenheit above average. Records may be in jeopardy in a number of major U.S. cities, with highs well into the lower 100s across Georgia and the Carolinas, for instance.
More than 50 million Americans are in line to experience temperatures above 100 degrees, and it’s likely heat advisories and excessive-heat watches and warnings will be issued as the event nears. It comes less than a week after much of the Southwest, the Plains and the Ohio and Tennessee valleys dealt with stifling heat and humidity.
It all stems from the same parent heat dome that has been languishing and refusing to budge from its perch over North America. It initially built into the Western United States. Its next act will feature an expansion and intensification of its sphere of influence, with the ridge of high pressure soon to sprawl across the entire Lower 48.
How hot it’s going to get
The next big pulse of heat will be established Tuesday of next week and will really dominate from Wednesday onward. According to a plot produced by Tomer Burg, a graduate student in atmospheric sciences at the University of Oklahoma, temperatures at the 850 millibar level — roughly a mile up — will reach top-tier records in the skies over Alabama, Georgia and South Carolina. When it’s hot in the sky, it’s even toastier at the surface. That indicates decent chances of triple-digit heat.
“High temperatures alone (but more certainly heat indexes) Wednesday, Thursday, and Friday could necessitate Heat Advisories across portions of the area,” wrote the National Weather Service office in Peachtree City, Ga. The combination of highs pushing 100 degrees and Gulf humidity will make for heat indexes potentially nearing 110 degrees.
As for actual air temperatures, Atlanta is looking at a forecast of 98 degrees on Tuesday and 100 on Wednesday and Thursday. Macon could see highs around 102 or 103 degrees. In Macon, the temperatures could beat records of 101 degrees set in 1925 and 1988 on Wednesday and Thursday, respectively. Atlanta will likely topple daily records that have stood since World War II.
Nashville is predicted to see a high of 101 degrees on Tuesday and Wednesday — both likely topping records from 1988 — and a high of 100 degrees Thursday, which may fall a degree short of tying a record.
The temperature in Birmingham, Ala., will be around 100 on Tuesday and 102 on Wednesday and Thursday, readings that will be within a degree or two of daily records. Most of the remainder of the South, including South Carolina, Mississippi, Texas and interior Louisiana, will be around 100 degrees for three or more days in a row. Houston is likely to hit 100 degrees during the spell, and overnight lows in some places, like Dallas, might not dip below 81 at night.
Dew points, meanwhile, will sit in the mid- to upper 60s along the Interstate 20 corridor and the lower 70s along Interstate 10, combining with the heat to yield heat indexes in the 105- to 110-degree-range. This could be especially problematic for low-income residents, the elderly and other vulnerable populations who may not have the means to escape the brutal heat.
The heat now
On Friday, the ongoing heat across the eastern United States was beginning to pull back south a bit as a cold front collapsed toward the Gulf Coast. Heat advisories were still in effect for parts of the coastal Carolinas, the Deep South, the Ozarks and the central Plains, but alerts had been dropped over the Midwest and parts of the Tennessee Valley.
Heat advisories were issued in Montana ahead of the next pulse of anomalous heat, which is expected to bring highs in the upper 90s to near 100 degrees on Saturday. There’s a chance that Glasgow could nick 100 degrees; the average high this time of year is about 79.
Both Aberdeen and Pierre, S.D., are looking at highs of 100 degrees on Saturday, with upper 90s to near 100 ubiquitous across the Plains, the lower Mississippi Valley and most of the South ahead of the southward-sagging cold front. The front probably won’t make any additional southward progress before the next pulse of arriving warmth scours out any extant temperature air. Instead, the sauna-like steam bath is about to reign once again.
Heat dome dominates
The heat is tied to an upper-level ridge, or a crest in the jet stream. This roadblock shunts fierce high-altitude winds and storminess to the north over Canada and the Great Lakes, with sunshine and high pressure building in to the south. High pressure areas bring sinking air, which warms up and dries out. The result? The heat dome bakes the landscape beneath it.
Through the weekend and into early next week, an “omega block” pattern will keep the heat dome in place over the Mississippi River. An omega block consists of two low pressure systems flanking the high, one on either side, and the trio of weather systems interlocking like meshed gears. That allows each to sit in place and spin for an extended period of time. That means the high won’t easily budge.
Eventually the omega block will break down around Tuesday, allowing the heat dome to expand west and flatten, occupying most of the Lower 48, before intensifying late in the week. That will mean even more significant heat for the northern Plains, with toasty temperatures for just about everyone else too.
The Climate Prediction Center continues to forecast elevated temperatures for much of the continental United States for the next week or two. Heat domes are ordinary staples of the summertime, but are made more intense by human-induced climate change.