A significant and unusually warm storm system will bring a heavy soaking and potential flooding to much of the eastern half of the nation between Friday and Sunday. A widespread two to five inches of rainfall is possible from the Lower Mississippi Valley to New England.
Meanwhile, a multiday severe thunderstorm event may unfold from eastern Texas through the Deep South, bringing the risk of tornadoes to the forecast late in the week.
The potentially dangerous weather looms, thanks to a pulse of anomalous warmth that will streak across most of the eastern half of the nation between Thursday and Saturday.
The upper-level disturbance responsible for the impending meteorological mischief is over the interior portions of Alaska. The pool of cold air associated with it will spill over the western Lower 48 as we head toward Wednesday and Thursday. Ahead of it, warmth and moisture will surge from the Plains eastward.
On Friday, a lobe of that mid-level chill ― banked up over the West Coast — will pinch off. From there, it will barrel east and eventually northeast, spawning a zone of low pressure that will trigger the stormy weather and burst of warmth out ahead of it.
By Saturday, the stormy low-pressure zone should be centered near Arkansas. Ahead of it, a ripping low-level jet stream will shuttle copious moisture and unstable air northward. That will lend itself to producing heavy/flooding downpours over the Ohio Valley while fostering severe weather in the warm, muggy air to the south and east. Eventually that system will make a run at the Northeast over the weekend.
The severe thunderstorm threat
Friday and Saturday are the days to really watch for severe weather. On Friday, the area to watch will stretch from East Texas into northern Louisiana and Mississippi. That’s where the corridor of greatest likelihood of impactful storms lies, but a broad area between the Interstate 35 corridor and Mississippi River will be in play for potential rotating, or supercell, thunderstorms. In addition to tornadoes, there will be a risk for damaging winds. Hail does not appear to be a primary concern.
On Saturday, the threat shifts east, covering a broader area from eastern Louisiana east through Alabama and as far north as Nashville. Of course, in coming days we’ll be able to better narrow down with greater specificity the areas most at risk for severe weather.
With a stagnant high-pressure ridge centered offshore of the Southeast, the low-pressure system sparking the severe weather will be deflected up and around it. The axis of heaviest precipitation will extend from the Tennessee and Ohio valleys, gently curving through the central Appalachians and eventually into interior New England. It may remain west of Interstate 95 corridor in the Mid-Atlantic and Northeast, although cities such as Washington, Philadelphia and New York may see a burst of heavy rain Saturday night.
Saturday will feature heavy rain and isolated flash flooding west of the mountains, a fire hose of moisture targeting cities such as Memphis, Louisville, Columbus, Cincinnati and Pittsburgh. A widespread two to four inches, with localized six-inch amounts, is possible through Sunday in those regions.
That area has already seen more than its fair share of rainfall in 2019.
The main slug of moisture scoots to the northeast on Sunday. Central and northern New England appear favored for heavy rainfall at this juncture, but all of the area is in play for potentially excessive rainfall. One to three inches is possible there, with a few four-inch amounts.
With this pattern in place, featuring a persistent stream of warm, moist air over the eastern United States, there are reasons to believe that another heavy rain event could unfold over similar areas in seven to 10 days.
Starting Thursday and Friday, temperatures will turn abnormally mild over the eastern United States. Many areas will see high temperatures 20 to 30 degrees above normal either Friday or Saturday.
Atlanta could hit 70 degrees on Saturday in the steamy air ahead of the front. The average high this time of year is 52 degrees.
Columbia, S.C. — which is around 57 this time of year — is likely to hit 70 degrees on Friday, Saturday and Sunday. In fact, upper 70s are possible on Saturday.
In Washington, a high of 66 degrees is anticipated Saturday. That’s the average high on April 14.
The mild pattern may ease Sunday into early next week before another surge of warmth in the middle of next week. For the week of Jan. 9 through 16, temperatures will average 10 to 15 degrees above normal in many areas in the eastern United States. It doesn’t look as though the mercury will fall back toward seasonable levels until perhaps somewhere around the week of Jan. 19.