Tornado outbreak of April 16-20, 2009 (Blackford)

the Tornado outbreak of April 16-20, 2009, also called by some the 2009 Super Outbreak, was a devastating tornado outbreak that struck the United States during mid-April of 2009.

The outbreak was the largest since the 1974 Super Outbreak, and remains the fifth-largest tornado outbreak or outbreak sequence on record.

The storm produced what was for a time the deadliest tornado in Indiana state history, the 2009 Hartford City tornado.

Meteorological history
On April 10, 2009, a extremely powerful subtropical cyclone moved onshore in Oregon.

By April 14, the system was stationed over North Dakota, and was producing a late season winter storm towards it's west.

April 16 -
On April 15, the subtropical cyclone pulled into Canada, producing heavy snow across large parts of North Dakota, the SPC had been concerned as far back as April 8 of the possibility of severe thunderstorms popping up in Oklahoma on that day.

Meanwhile, warm air moved into parts of the upper Midwest on April 15, allowing snow to transition into rain across parts of South Dakota, Minnesota and Nebraska that afternoon.

Early on April 16, towards the northern part of the Great Plains, CAPE levels of roughly 3,000 J/kg were recorded in parts of Nebraska. Not only that, but dew points were expected to reach 65-75°F that day. The SPC became concerned for the possibility of violent tornadoes and upgraded the region to a Moderate Risk in the 06Z outlook.

Meanwhile, towards the southern Great Plains, a volatile atmosphere was evident, with CAPE levels exceeding 4,500 J/kg. Not only that, but dew points were expected to reach as high as 80°F that day. This worried the SPC, and they issued a High Risk of Violent Tornadoes in the 06Z outlook.

The first tornado of the outbreak touched down in North Dakota, outside of the thunderstorm risk area, around 1741Z, when a brief EF0 tornado damaged a outhouse.

Meanwhile, by 19Z, violent thunderstorms began to pop up in the High Risk area, with the first EF4 tornado of the outbreak severely impacting various buildings southwest of El Reno around 2020Z.

However, a unexpected cap appeared in the atmosphere, which resulted in the High Risk being cancelled at 20Z, in the end, 9 tornadoes touched down on April 16 in the southern Great Plains, while 10 touched down in the northern Great Plains.

The event was seen as a bust.

This is a work-in progress!