We at LifeStation have never heard of a heat dome but it seems to be quite real and very dangerous. The heat and humidity are extremely dangerous, particularly for seniors. If you have air conditioning, turn it on, stay home and keep your medical alarm handy just in case you start to feel dehydrated or over-heated. If you are without a/c, find a friend or neighbor or visit a cooling center.
In any case, stay cool, drink lots of fluids and be safe.