Storms over the District on May 15. (Jim Havard via Flickr)

Many of us in the Washington region plan to spend considerable time outdoors this holiday weekend and hope the weather won’t get in the way. The latest forecast contains both good and bad news.

Yes, there is the chance of showers and storms each of the three days, but they won’t happen all the time and everywhere. For the most part, storms should tend to concentrate between the midafternoon and early-evening hours. They should be hit or miss, with the greatest coverage Sunday. Memorial Day has the smallest chance of storms, but they are still possible.

Because storms that develop might unload very heavy rain and generate lightning, it will be important to stay weather-aware and flexible, and have a plan to seek shelter if storms threaten. Storms may be slow movers. Flash flooding is another possible hazard to be aware of given the saturated ground.

In addition to monitoring the storm threat, keep in mind it will be very humid all weekend even when it’s not raining, so remember to stay hydrated.

Here’s a day-by-day assessment of what we might expect:

Saturday

  • Chance of storms: 30 to 40 percent, highest chances in southwest and western areas
  • Most likely window: 2 to 7 p.m.
  • High temperatures: 85-90, feels like 90-95

What you’ll notice most about Saturday is the big increase in humidity. Dew points jump up to near 70 degrees, indicative of uncomfortably muggy conditions.


(The Washington Post)

With air temperatures climbing close to 90, the combination of heat and humidity will provide plenty of fuel for storms that form. But we don’t think they’ll be widespread.

Models show the possibility of hit-or-miss storms first popping up in our west and southwest areas as early midday or early afternoon. As the atmosphere’s steering flow is weak, they might not make a lot of headway into the immediate metro region before collapsing in the early evening. But any that survive could generate heavy downpours.

Sunday

  • Chance of storms: 60 percent (everywhere)
  • Most likely time window: 3 to 8 p.m.
  • High temperatures: 83-87, feels like 87-90

It’s another sticky day. A weak front to our north may provide a focus for more widespread afternoon and evening storms. All of the models suggest there will be areas of rain and the high-resolution NAM model, while not terribly reliable this far out, shows a broken line of storms over the region around 5 p.m.


High resolution NAM model shows showers and storms over the region at 5 p.m. Sunday.

This is the most likely day that outdoor activities could be interrupted, so a Plan B is a good idea in case storms threaten.

Monday

  • Chance of storms: 20 to 30 percent, highest chances west and south of Beltway
  • Most likely window: Noon to 6 p.m.
  • High temperatures: 82-86, feels like 86-90

The front, which may act as a focus for storms Sunday, probably lifts far enough northeast that there’s no strong trigger Monday. That said, it’s again humid. Hit-or-miss storms could still pop up in the afternoon. Models tend to show the best chance south and west of the immediate area, but it’s kind of a crapshoot.