More than two million people in Oklahoma and the Texas Panhandle are in harms way after the National Weather Service’s Storm Prevention Centre announced a threat level-five warning – their highest – for violent tornadoes as well as warnings for significant hail and flooding lasting into Monday night.

They’ve also designated the storm a ‘Particularly Dangerous Situation’ or PDS, their most dire classification. This is the first time in two years that the National Weather Service has issued such high warnings for a storm.

According to the SPC, the probability of all three weather types is 95%. The only other storm to have had such high probabilities in the SPC’s history, was an Alabama storm in 2011, the centre pointed out.

Marble-sized hail has already been reported in Oklahoma and baseball sized hailstones are a possibility.

Tornado tears through Alabama killing 23 Show all 15 1 /15 Tornado tears through Alabama killing 23 Tornado tears through Alabama killing 23 Tornado in Dothan, Alabama on March 3 AFP/Getty Tornado tears through Alabama killing 23 Debris and a damaged house following a tornado in Beauregard, Alabama on March 3 Scott Fillmer/Reuters Tornado tears through Alabama killing 23 People walk amid debris in Lee County, Alabama AP Tornado tears through Alabama killing 23 Damage in Lee County, Alabama AP Tornado tears through Alabama killing 23 A funnel shaped cloud on the I-10 near Marianna, Florida on March 3. Tornado warnings have been issued across the southeast of the US AP Tornado tears through Alabama killing 23 House debris following a tornado in Beauregard, Alabama on March 3 Scott Fillmer/Reuters Tornado tears through Alabama killing 23 A tornado in the distance at Warner Robins, Georgia on March 3 @KEITH_IRWIN/Reuters Tornado tears through Alabama killing 23 A fallen pylon lies across Route 280 in Lee County, Alabama AP Tornado tears through Alabama killing 23 Fallen trees lie across a road following a tornado in Beauregard, Alabama on March 3 Scott Fillmer/Reuters Tornado tears through Alabama killing 23 Damaged trees seen following a tornado in Beauregard, Alabama on March 3 Scott Fillmer/Reuters Tornado tears through Alabama killing 23 People look on at clean-up efforts following a tornado in Beauregard, Alabama on March 3 Scott Fillmer/Reuters Tornado tears through Alabama killing 23 People clear fallen trees and debris from a road following a tornado in Beauregard, Alabama on March 3 Scott Fillmer/Reuters Tornado tears through Alabama killing 23 Fallen trees following a tornado in Beauregard, Alabama on March 3 Scott Fillmer/Reuters Tornado tears through Alabama killing 23 Tornado in Dothan, Alabama on March 3 AFP/Getty Tornado tears through Alabama killing 23 Emergency responders work in the scene amid debris in Lee County, Alabama AP

In anticipation of the storm Oklahoma City and Tulsa, Oklahoma, closed down schools for the day, while Tinker Air force Base evacuated some of its aircraft, CNN reported.

Veteran storm chaser Mike Smith cautioned others against braving the storm. “To: #StormChasers, I believe I am the only one of the original, 1972, chasers still chasing. But, I will not be out today. It is too dangerous. The tornadoes will be difficult to see and too dense & flooding could cut off escapes.” he wrote in a tweet.

The storm comes on the 6th anniversary of the 2013 Moore tornado that killed 24, including 9 children, in the town of Moore, Oklahoma.