The 1991 California “Miracle March”: Precipitation Myth or Miracle?

Abstract The term “Miracle March” is colloquially used in California to describe an anomalously wet spring that alleviates drought conditions caused by a winter precipitation deficit. This study centers on the influential water year 1991, which is the standard reference point for this phenomenon. The spring precipitation impact on water year totals and the geographic extent of the spring precipitation anomaly during the 1991 “Miracle March” (MM91) is without equal in the observational record. This exceptional precipitation episode was initiated by a week-long sequence of extreme atmospheric rivers that started landfalling on February 27th. To this day, MM91 is routinely referenced as a basis for hope of drought alleviation in California water management. MM91 demonstrates the role that an exceptional spring precipitation season can play in determining the cessation of drought, but a historical analysis also shows just how unusual such conditions are.