Now that we know that a 'dirty nuclear bomb' plot targeted DC, we have good reason to plan ahead for such an emergency:
Evacuation tips by Humane Society

Make sure you have a current ID tag on your dog(s)' collar along with his rabies ID tag.

Carry a photo of your dog for identification purposes.

Call hotels in safe areas and ask if you can bring your pets; ask hotel managers if "no pets" policies can be lifted during the disaster. Motel 6, Studio 6 and Red Roof Inns all welcome pets to their properties. Call (800) RED-ROOF or (800) 4-MOTEL6 for info.

If that doesn't work out, call friends, family, veterinarians and boarding kennels in safe areas to arrange for foster care.

Pack a week's worth of food, water, and other supplies such as cat litter and medication.

Keep a list of emergency phone numbers (veterinarians, local animal control and humane societies, Red Cross, etc.) accessible.

Bring your dog's vaccination records and health records with you

If you smell smoke, keep your dog inside. The Denver Channel Jun 12 2002 1:10PM ET [Moreover - Animal news]

DC endures a heat wave For the last several days, when we walk our dog he sneezes and coughs and wants to go back inside immediately. We put  ice in his water dish last night and he immediately fished out the largest ice block. He pranced around the house with the ice block in his mouth, with water streaming down his face and a trail of water following him. It was hilarious. Yesterday's heat wave included 94 degrees, high humidity, and code red air pollution.