The storm could bring heavy rain, frequent lightning and damaging wind gusts. The potential for heavy rain has prompted the National Weather Service to issue a flood watch from 2 p.m. to midnight.
“Thunderstorms this afternoon and evening could produce heavy rainfall in excess of 2 inches per hour,” the weather service wrote. “Localized repeated or prolonged thunderstorms could result in flash flooding in flood-prone urban and suburban areas.”
As temperatures across the Washington, DC area warm again into the upper 90s or near 100 by early afternoon, storms could begin to form near the Blue Ridge Mountains and move eastward during the late afternoon and early evening.
Some storms will be slow-moving, which could cause flooding in the area despite the drought that has affected much of the region in recent weeks.
The storm will ultimately help drive away the record heat, but Washington, D.C., could see temperatures reach at least 100 degrees for a fourth straight day, which would tie the longest streak on record.
A quick rundown of storm possibilities:
- Storm timing: The storms are expected to move from west to east and be at their strongest between 3 PM and 9 PM, with a possible storm formation around 2 PM.
- Rainfall chance: Rainfall amounts will vary widely but average between 0.5 and 1.0 inch. Areas experiencing repeated heavy rainfall can expect 2 to 4 inches of rainfall within a few hours, posing a risk of flooding.
- Wind threat: Sporadic, damaging wind gusts could down trees and power lines, causing power outages.
- flood: Flood-prone streams, rivers and areas with poor drainage will be most affected.
Stormy debate
The threat of Wednesday’s storm comes with the approach of a much-anticipated cold front and the end of a brutal heat wave.
High-resolution models predict that the initial storm cluster will develop over the western mountain ranges, with a cluster or short arc of storms moving eastward. Storms developing in the early afternoon will target northern regions first, then spread to the south a little later, possibly becoming locally concentrated in the evening.
At higher levels, disturbances in the upper air currents will tend to cause the air to rise, and that rising may be more intense and widespread than it has been over the past few days.
The region is under a possible severe thunderstorm watch from the Met Office’s Storm Prediction Center, which places the area at Level 2 out of 5 on the risk of severe storms.
The flood threat stems from several factors. First, a repeat storm is possible within the next few hours later today. Second, the deep moisture content of the atmosphere is very high. Third, deep, warm air masses foster efficient development of torrential rain, even in storms that do not meet the official severe criteria for wind or hail. Fourth, the thresholds that trigger flash flooding are lower today in areas that have been drenched over the past few days.
Another major threat is wind damage caused by linear, localized gusts of wind called downbursts. In this type of air mass situation, rain-filled bubbles suddenly release a torrent, dragging air downward. Some of the rain cools through evaporation and accelerates further downward. These bubbles impact the ground in violent explosions. Wind gusts can reach 60-80 mph.
The good times continue
By just before 10 a.m. Wednesday, temperatures had topped 90 for the fifth straight day, the 29th time this summer, following an overnight low of 83. The high temperature is expected to be 98 degrees, but has exceeded expectations in recent days, already reaching 95 degrees by midday.
Consecutive high temperatures on Sunday, Monday and Tuesday were 101, 102 and 104 degrees, making them the hottest days since the Dust Bowl began.
The average temperature on Tuesday was 92 degrees (the average of the day’s high and low temperatures), the fifth warmest since records began in 1872.
In the past four weeks, there have been 17 days when temperatures reached 95 degrees or higher, matching the most four weeks on record.
This summer has been the hottest yet, with the most days with temperatures reaching 90, 95, 98 and 100 degrees or higher all on record.
Temperatures will be milder as a cold front moves through Wednesday night, but summer-like highs in the 80s and near 90 degrees are still expected over the next few days.
Jason Samenow contributed to this report.
