The first tornado warning for the town of Moore went out at 2:40 p.m. for the massive tornado as it touched down to the west in Newcastle, Oklahoma, but the National Weather Service was giving informal warnings even before that.
Here are a series of Tweets from @NWSNorman that were also posted simultaneously on their Facebook page:
2:08 p.m.: "Storms developing near Blanchard and Tuttle, moving NE at 30mph. Stay alert Norman, Moore, and S OKC. Not severe yet."
2:30 p.m.: "people in south OKC, Moore and north Norman need to pay VERY close attention to the storm near Newcastle"
2:34 p.m.: "One warning forecaster focusing on big supercell west of OKC"
2:39 p.m.: "storm west of Newcastle is intensifying and showing some rotation. Stay alert! No tornado warning yet"
2:40 p.m.: "TORNADO WARNING for OKC metro! Developing tornado new Newcastle moving E 20 mph. Take shelter!!" -- this warning also included the town of Moore.
Another tweet at 2:45 p.m. mentions Moore is in the path and is giving safety tips.
At 2:56 p.m the tornado is now on the ground in Newcastle -- 16 minutes after the warning was issued. It's heading for Moore.
At 3:01 p.m., the National Weather Service upgraded the warning to a "Tornado Emergency" for Moore and south Oklahoma City. A Tornado Emergency is a step above a "Tornado Warning" and is used when a massive and extremely large tornado is imminent, as was the case here.
3:02 p.m.: "LARGE VIOLENT TORNADO moving toward Moore and SW OKC. Take cover right NOW!! Do not wait!!"
3:03 p.m.: "This is as serious as it gets for SW OKC and Moore. Please seek shelter now!"
3:14 p.m.: "Large, deadly tornado moving into Moore near 134th and Western"
According to Mike Smith's blog recapping the warnings, the tornado officially entered the town of Moore at 3:16 p.m.
3:19 p.m.: "TORNADO Approaching area near Warren Theater in Moore! Please take shelter. This is as bad as it gets"
3:21 p.m.: "TORNADO EMERGENCY for the City of Moore. Get as far inside a sturdy building as you can. Cover up! Do not wait!"
Then, this daunting tweet:
3:22 p.m.: "The tornado is so large you may not realize it's a tornado. If you are in Moore, go to shelter NOW!"
The tornado would push through the city until 3:32 p.m. dissipating at 3:36 p.m. after creating a path of destruction 17 miles long and at least a 1.3 miles wide.
But residents of Moore had over half an hour under an official tornado emergency to seek shelter, and had been given initial warnings nearly an hour in advance.
Long range forecasting advancements
As forecasting models get better and better with new technology, it allows meteorologists to get an earlier heads up on the potential for severe weather development. NOAA's Storm Prediction Center issues a daily "Convective Outlook" that highlights potential threats across the nation out as much as 4-8 days in advance. This map was for Tuesday, May 21:
As I mentioned earlier, forecasters started getting worried about Sunday's storms as early as last Wednesday and concern became heightened on Friday when it looked like a very volatile mix of severe weather ingredients were set to mix together in that area.
As the time approaches, higher-resolution forecast models that focus on the near term can get a much better grip on which areas will have strong potential for severe weather. It's up to the Storm Prediction Center to issue Severe Thunderstorms or Tornado Watches across the U.S. It did so in Moore's case about 2 hours before the storms struck, but it is up to individual National Weather Service forecast offices to put out warnings, as the local office in Norman, Oklahoma did.
Hail to the Doppler Radar
But perhaps the single biggest weapon meteorologists have in forecasting tornadoes is our NEXRAD Doppler radar. These high-powered radars can see the storms in 3-D and can now pick up on rotation inside a thunderstorm and potential tornado development even before the funnel forms, allowing for even more warning time.
If you've been watching the live coverage of the storms from local meteorologists in Oklahoma, you might have seen a somewhat unfamiliar radar product that shows red and green blobs instead of the traditional green/yellow/orange/red/purple blobs of a rain-detecting radar.
This is what's called a "velocity scan" and what the radar is doing is what you would expect a "Doppler" radar would do best -- measuring the doppler shift of particles. This data is extremely useful in detecting rotation.
Here is one such picture of the radar as the tornado was in Moore:
The red lines indicate particles that are coming toward the radar beam while green indicates going away. The radar site is noted by the "TOKC" dot there. This would generally just indicate a northeast wind across the area -- reds to the northeast show wind coming at the radar; green to the southwest shows wind going away. But note the "couplet" of red and green swirling around Moore-- that's the radar picking up the strong rotation -- the red area showing the wind blowing away, the green to the left blowing toward the radar.
This particular case it shows up quite obviously due to the size of the tornado but the radar can pick up much more subtle nuances of rotation when storms are in their infant stages.
The radars can also detect the debris being spun around in a tornado -- which can give further confirmation to a forecaster that a tornado is on the ground, even if it's hidden from sight by heavy rain or darkness.
The radars can now show storm details down to street level, and software can compute the storm's expected track to give towns an expected arrival time down to the minute.
Cell phones have become personal weather alert systems
It used to be that emergency managers relied heavily on NOAA Weather Radios, tornado sirens, and the Emergency Broadcast System to warn areas of impending tornadoes. They still do, and NOAA weather radios remain a must-have in severe weather country -- they are equipped to where they will sound an alarm if a tornado warning is issued, even if the radio is off.
But perhaps now the greatest advancement in warning the public is the cell phone. Do you remember back in December when we had a blizzard warning for the Cascades and everyone's cell phones chirped to life with the warning?
People told stories of being at the mall or in a public place and how eerie it was when everyone's cell phone started going off at the same time. It was a bit of a mistake here in that the warning was intended just for the mountains, but since many city areas share their county with the Cascades, the alert went out county wide and inadvertently covered some metro areas.
That same technology is used for tornado warnings and of course, is much more relevant in the Midwest. Now, when an urgent warning is issued by the National Weather Service, your phone acts just like those weather radios and can warn you of impending danger no matter where you are.
So with advancements in forecast technology and the much broader reach of ways to alert the public, we are much better off than we were just even 10-15 years ago. Sadly, due to the tornado's incredible strength, even with several minutes' warning time a lot of the shelters directly in the storm's path were no match for the sheer power of the winds, but there were still likely many lives saved by the timely warnings.