The air is set to turn warm and a bit humid Thursday afternoon and, when a cold front runs into that steamy air, a line of scattered storms could organize and charge through the D.C. metro region.
The most likely window for storms is between 2 p.m. and 8 p.m., and a few storms may contain damaging winds and/or hail. Any line of storm that forms is likely to be fragmented, meaning that some areas may get hit hard, while others are passed over.
Storms are likely to first pop up in our western areas in the midafternoon and exit our eastern suburbs in the hours before sunset.
The overall storm coverage is Thursday’s greatest uncertainty, as some models suggests that storms will be really hit or miss, while others show a more solid line coming through.
Thus far this spring, little in the way of thunderstorm activity has affected the Washington region. Much of April was cooler than normal, so the atmosphere was starved of the moist, unstable air needed for storms to pop.
But May has been unusually warm, about 8 degrees above normal. On Thursday, winds from the south will draw up the latest pulse of warmth, and highs are expected to reach the low to mid-80s.
The atmosphere will then be sufficiently heated to fuel storms developing along the cold front moving in from the west. The measure of this fuel, known as convective available potential energy (CAPE), could exceed 2,000, a large number for our region.
A second ingredient, vertical wind shear, is also favorable for storm development. This change of wind with altitude helps sustain storm updrafts.
Given these ingredients, the National Weather Service Storm Prediction Center has placed the D.C. area in a marginal risk zone for severe storms.
While a marginal risk declaration signifies the second-lowest level on the Storm Prediction Center’s 0-to-5 scale, pockets of wind damage and/or large hail can develop in these situations.
The risk isn’t higher because the cold front coming through isn’t particularly strong and storms that form will be far removed from its associated low-pressure center, where the air is rising most rapidly.
Computer models suggest that the storm activity should move through quickly, with clearing in most areas by sunset or shortly after.
We’ll have a new update on this storm potential on Thursday morning.