Here is the severe weather rundown for the period from now until 8am EDT tomorrow. This will be a major event.
There is a tornado risk (5% is significant in this category) in NYC and nearby areas (including Hartford).
A derecho is likely in the hatched area where winds may gust above 75mph causing power failures and downed trees.
In the non-hatched areas, winds may gust above 60 mph with 15% (yellow) the significant threshold.
Finally, these are the probabilities of hail ≥1" in diameter. Fifteen percent is the significant threshold.
I have safety suggestions for people living in these areas here.
Air travel is already bad and it is only going to get worse:
San Francisco has slowed down takeoffs and departures due to low clouds.
Thunderstorms are causing delays at Newark, JFK, LaGuardia, Philadelphia, Midway and O'Hare. With many more thunderstorms expected as the day progresses, air travel will be a real mess.
If you are planning to travel today, please go to my Airline Travel Survival Guide.
AccuWeather is going to live blog the storms.
I'll have an update at midday.