At first today’s forecast just looked a little bit annoying: a 30 percent chance of thunderstorms in the late afternoon which, in the words of our esteemed pals at CapitalWeather.com, we’d venture to say “those odds are too low to go changing any plans yet, but high enough to keep an eye to the sky and on radar just in case.” In other words, we’re packing up to head to a barbecue right now, potential showers be damned.

But the National Weather Service has just issued a Tornado Watch in effect from now until 10 p.m. Of course, a watch is a pretty low-level weather alert, indicating that weather conditions are favorable for the development of severe thunderstorms that are capable of producing tornadoes — not to be confused with a tornado warning, which usually means take cover, now! Still, not exactly the kind of news we like to get on a day when we’re supposed to be drinking beer in the sun and have clear views of the sky to see fireworks.

So, what to do? Probably nothing too different still, except plan on bringing an umbrella or a parka wherever you do go, plus something plastic to sit on if the grass is wet later on. And obviously, if you were planning on swimming today and you see any lightning, get out of the pool immediately. In the event tonight’s fireworks display is actually canceled due to weather (and we have no reason to believe that will happen), a raindate will be determined and announced.

UPDATE: The National Mall was briefly evacuated around 5 p.m., forcing the thousands gathered for 4th of July festivities to take shelter in nearby monuments and federal government buildings. By 7 p.m. the Mall was re-opened, though everyone had to pass back through security checkpoints set-up in the area again. The Post is reporting the Capitol Fourth concert and fireworks are still on schedule. A tornado watch is still in effect until 10 p.m.