Los Angeles' weather is not always perfect, according to meteorologists Craig Herrera and Craig Herrera, a meteorologist at Fox Weather, who spent two years working in L.A. and Daniel Swain, a climate scientist for the California Institute for Water Resources, who attributes hydroclimate whiplash to the extreme weather. The National Weather Service has issued most severe weather warnings over the past 20 years, with an average of 150 marine warnings for boaters, 10 to 20 severe storm warmings, and occasional tornado warnings. The marine layer, created from cold waters from the Pacific Northwest, contributes to smaller tornados than those seen in Tornado Alley due to the higher tornado density in the Los Angeles basin. However, Todd Hall, a warning coordination meteorologist for the National Weather Services, also knows that L. Angeles is a very tornado prone area and has a tendency for very extreme weather events.