* Severe thunderstorm watch until 1 a.m. in Southern Maryland and Stafford County in Va. *
11:25 p.m. - Severe thunderstorm watch cancelled in immediate metro area
While some showers and storms may still move over the region from the west, they’ve generally been weakening. As such the severe thunderstorm watch for the region has been discontinued.
Some heavier storms stretch from Culpeper to Fredericksburg heading in the direction of southern Maryland, so the severe thunderstorm watch stays in place in this zone.
10:25 p.m. - Numerous showers/storms likely into overnight hours but intensity should decrease some
We no longer have any storm warnings in the region but there still are still numerous showers and storms to the north and to the west of the District pushing southeast toward the immediate area along a cold front entering the region.
Over the next few hours, many areas are likely to get wet but severe storms, if any more develop, should be rather isolated. In general, storm intensity is weakening.
When it’s not raining, expect mostly cloudy, warm and muggy conditions with lows in the mid-to-upper 60s.
Looking ahead to Memorial Day, it should be stay mostly dry, but clouds will be hard to shake. Let’s call it mostly cloudy for the duration with warm and muggy conditions. Highs will top out in the mid 80s with just a slight chance of a shower or thunderstorm in the afternoon. Warm and muggy tomorrow night with lows in the mid to upper 60s.
Unless new severe storms develop, this will be the last update of the evening.
9:40 p.m. - Severe thunderstorm warning for Columbia and Baltimore until 10:15 p.m.
A rather intense thunderstorm stretches from Baltimore southwest along Interstate 95 through Columbia back into North Laurel. Heavy rain, lightning and wind gusts to 60 mph are possible with this storm as it pushes southeast around 35 mph. Glen Burnie and Severna Park are in its path.
9:30 p.m. update: Heavy storms span from Frederick to Baltimore along and just north of Interstate 70. While no warnings are in effect in this zone, there are pockets of heavy rain and lightning, so take it slow if traveling in this area.
Parts of northern Maryland did see some damaging wind gusts and downed trees from storms in the last hour, but the activity has weakened some.
9:15 p.m. update: The National Weather Service has issued a severe thunderstorm watch for the region until 1 a.m. A watch means conditions are favorable for severe storms, but not a guarantee and that you should stay alert. If a severe thunderstorm warning is issued for your location, on the other hand, it means a severe storm is imminent and you should seek shelter.
So far this evening, most of the thunderstorm activity has focused in northern Maryland and that may continue to be the case for the next couple of hours, at least.
4:10 p.m. update: Storms so far have been widely scattered (hit-or-miss) and subsevere, with just some brief downpours and a bit of lightning. We may see a few isolated showers and storms the next few hours, but most areas should stay dry though humid with temperatures in the low-to-mid 80s.
We expect the main storm activity to probably hold off until after sunset, in the 9 to 11 p.m. window. At that point, it’s unlikely we see a major outbreak of severe storms, but an isolated storm or two could be intense and we’ll monitor.
Original post from early afternoon
A hot and humid air mass has moved over Washington. It could fuel strong to severe thunderstorms late this afternoon and this evening as a cold front sinks south into the region.
Storms could roll through the D.C. area in two rounds. The first wave — which may bring more hit or miss storms — is expected between roughly 3 p.m. and 6 p.m.
A second more widespread line of showers and storms is then possible after sunset.
Heavy downpours, gusty winds, and lightning are likely in storms that form. Isolated storms may contain damaging winds and hail, and there’s an outside chance of a tornado.
The National Weather Service has placed the region in a slight risk zone for severe storms, Level 2 out 5.
With so many outdoor activities planned on this Memorial Day weekend afternoon and evening, it’s important to stay weather aware and have a way of receiving weather warnings. If thunder roars, head indoors.
Approximate arrival time for storms...
First round — more hit-or-miss (30 percent chance of measurable rain in any location)
- 2:30 to 4 p.m. western areas
- 3:00 to 4:30 p.m.. immediate area, including the Capital Beltway
- 3:30 to 5 p.m. areas east of Interstate 95
Second round — potentially more widespread (60 percent chance of measurable rain in any location)
- 7:00 to 9 p.m. western areas
- 8:00 to 10 p.m. immediate area, including the Capital Beltway
- 9:00 to 11 p.m. areas east of Interstate 95
All clear: After midnight
Storm duration: 30 to 45 minutes or so
Chance of measurable rainfall in any location: 60 percent
Storm motion: West to east
Likely storm effects: Heavy rain, lightning, gusty winds
Possible storm effects: Damaging wind gusts, hail
Very small chance of: Large hail, brief tornado
Rainfall potential: Highly variable. Locally up to an inch or so in heaviest storms.
The NOAA Storm Prediction Center (SPC) has outlook carries a 15 percent chance of damaging winds and 15 percent chance of large hail, and a negligibly small risk of a tornado.
As of 12:30 p.m., in a special discussion from SPC, there is a 40 percent chance they will issue a severe thunderstorm watch.
The elements in play include a cold front sagging slowly toward our region from the north, and a very unstable air mass developing on southerly flow. An upper-level disturbance approaching from the Ohio Valley has increased the winds aloft, and thus the wind shear (change in wind with altitude). In fact, the wind shear is uncharacteristically large for late May.
Wind shear of this magnitude raises the prospects for organized storms, which can live longer and grow more intense. Additionally, the rotational energy in those winds can trigger the formation of bowing storm segments and perhaps even a super cell (rotating thunderstorm) or two.
One factor that argues against widespread severe storms include a fairly dry atmosphere immediately above the surface. Even in an unstable atmosphere, cloud updrafts can struggle against evaporation in this type of situation.
The convection-resolving cloud models portray two rounds of storms; an initial wave forming and moving off the mountains late this afternoon, which may be somewhat isolated to scattered. A second, more robust line of activity, resembling a squall line, appears likely in the 8 to 11 p.m. time frame. This line is more directly associated with the front itself.
If the initial, late afternoon round of storms is intense, it could steal some the energy used to fuel the second line.
Either round could feature pockets of damaging wind, in faster-moving segments of the storms that bow outward. There is an outside chance of an isolated tornado embedded in any bowing or notched-shaped storms (as they appear on weather radar).
A simulated radar snapshot of one possible scenario is shown in the image below, at 10 p.m. The later this second line develops and comes through, the better, since instability in the atmosphere will begin to wane around sunset.