National Weather Service rainfall forecast through Saturday morning. (PivotalWeather.com/PivotalWeather.com)

Severe weather tends to peak in spring, but the fall can often produce a second season of severe storms.

A developing system bringing the threat of violent thunderstorms in the south-central United States late Wednesday and Thursday is likely to generate heavy rain in the Mid-Atlantic on Friday. Strong thunderstorms and flooding cannot be ruled out in the Washington region. Over an inch of rain is possible, most of it probably falling Friday evening and night.

The responsible storm system is forming along a buckle in the jet stream in the central United States. Over the next several days, thunderstorms are likely to form near the cold front on its leading edge.


A storm system is beginning to form over the central United States. (College of Dupage)

Severe weather, including wind damage and the potential for strong tornadoes, is forecast to develop over parts of East Texas on Wednesday afternoon, spreading into Louisiana and Mississippi Wednesday night and then across the South into Thursday.

In its midday update on Wednesday, the National Weather Service’s Storm Prediction Center warned of a “substantial supercell/tornado threat” Wednesday night in parts of Louisiana and possibly Mississippi.


Tornado threat into tonight. (SPC/Google Earth/author)

The cold front associated with the ongoing storm system is slated to enter the Washington region by Friday afternoon.

There is some indication that it will progress fairly slowly as it moves through. When combined with a very moist November air mass, the potential for heavy rain and perhaps flash flooding may present itself.


This morning's GFS weather model showed plenty of rain locally from this upcoming storm system. (Capital Weather Gang and Pivotal Weather)

Weather models suggest that the heaviest rain may focus north and west of the Interstate 95 corridor, although placement is more or less a guess at this range.

Most models predict 0.5 to 1.5 inches of rainfall from this system across the entire area. Localized amounts could reach 2 to 3 inches where the heaviest rain is concentrated. While it has been a little drier lately compared with a few weeks ago, we remain waterlogged thanks to the year’s abundant rainfall.

The Weather Prediction Center is monitoring the potential for excessive rainfall on Friday that could cause flash flooding.


Excessive rainfall outlook over the next three days. (Weather Prediction Center)

In addition to the threat of heavy rain, we cannot rule out severe thunderstorms with strong winds, especially south and southeast of Washington. Plenty of wind shear, which is necessary for strong storms, will be available. However, instability — which acts as fuel for storms — may be limited — especially after dark Friday.

Should storms develop and become sustained, which is a small possibility, they may be able to tap into strong winds aloft and cause some wind damage or perhaps a tornado or two.

The heavy rain predicted will move our 2018 total up the list of the rainiest years on record, dating to the 1870s.

At 52.89 inches this year, the District is already in the slot of ninth-rainiest year on record, if the year ended today. This rain is likely to get us to at least seventh most on record.

Only three years have been able to top 60 inches in Washington: 1878 with 60.09, 2003 with 60.83 and 1889 with 61.33. Even if just an average amount of rain falls for the rest of the year, the 2018 total would rise to 59.11 inches, in fourth place in historical records.

Baltimore is even higher up in the rainfall rankings, with 57.14 inches so far this year. That’s good for the fifth-rainiest year, if the year ended now. Nos. 1 and 2 both top 62 inches, with 62.35 in 1889 and 62.66 in 2003. If Baltimore sees average precipitation going forward, it will be enough for the wettest year on record by about an inch and a half.

Beyond this storm, the pattern doesn’t change too much, at least right away. Another bout of stormy weather is probably on the way as we get toward Election Day.