EDIT 1: a Leak in the ground system of the mobile service tower delayed the launch so much that launch preparations ran into bad weather and the launch was scrubbed.
EDIT 2: Another abort shortly before launch. Sparklers were already burning excess hydrogen in the flame trench but a hold was called before the starboard engine ignited. Weather was good. That means there is a good chance we can see SpaceX launching today.
Delta IV Heavy Launch
The first attempt was scrubbed due to weather.
The second attempt experienced a rare hot abort, 3 seconds before liftoff. Engines were already firing but were automatically shut down due to a ground systems failure.
The third attempt was scrubbed because all 3 ground regulators had to be replaced. One failed regulator caused the abort of the second attempt.
The fourth attempt was scrubbed due to weather, as was a planned SpaceX launch.
Delta IV Heavy NROL 44 Mission Profile
United Launch Alliance (ULA) is launching an unspecified satellite on a Delta IV Heavy for the [National Reconnaissance Office (NRO)](National Reconnaissance Office) from SLC-37B, Cape Canaveral, Florida to geostationary orbit (around 36'000 km).
There are hints that the classified payload might be an Orion Signals Intelligence Satellite. These satellites capture radio signals with their 100 m diameter antenna.
Scott Manley talking about the particularities of Delta boosters:
Explaining the Delta Rocket Fireball
Watch live on Youtube: ULA Live Broadcast
Stream starts approximately 30 minutes before launch
Check your local time of launch at: www.timeanddate.com
Useful links to stay up to date on launches:
Spaceflightnow.com: Launch Schedule
Everyday Astronaut: Prelaunch Previews
Space News:
NASA Spaceflight nasaspacefight.com
TMRO: YouTube
Be aware, this is rocket surgery.
Small disturbances can lead to postponed launches. Making sure everything is just right is way cheaper than risking big fireworks.