Houston has mild winters in contrast to most areas of the United States. In January, the normal mean temperature at Intercontinental Airport is 53.1 °F (11.7 °C), while that station has an average of 13 days with a low at or below freezing. Snowfall is rare. Recent snow events in Houston include a storm on December 24, 2004 when one inch (2.5 cm) of snow accumulated in parts of the metro area. Falls of at least one inch on both December 10, 2008 and December 4, 2009 marked the first time measurable snowfall had occurred in two consecutive years in the city's recorded history. The coldest temperature officially recorded in Houston was 5 °F (−15 °C) on January 18, 1940. Houston has historically received an ample amount of rainfall, averaging about 49.8 in (1,260 mm) annually per 1981–2010 normals. Localized flooding often occurs, owing to the extremely flat topography and widespread typical clay-silt prairie soils, which do not drain quickly.

Answer this question, if possible (if impossible, reply "unanswerable"):  How many tornadoes does Houston usually get per year?
unanswerable