Laserfiche WebLink
2024 Hennepin County All -Jurisdiction Hazard Mitigation Plan <br />Volume 2 — Hazard Inventory <br />4.3.6.6. Chronologic patterns (seasons, cycles, rhythm) <br />Extreme rainfall has been observed from April through November, but peak probabilities are generally <br />from June through August, and to a lesser extent, September. The frequency of 3 and 4-inch rainfall peaks <br />during July. <br />Twin, Cities Heavy Rainfall's by Month, 1 71-2015 <br />2 <br />" events <br />26 <br />i ,, " events <br />" events <br />24 <br />20 <br />16 <br />12 <br />6 <br />........... w ... ...... <br />1 ... ;ems .... .v....... w . . <br />Jan Feb Mar Apr May Jul' Jul <br />Aug <br />Sep Oct Novi De <br />Graphic of 2, 3, and 4-inch daily rainfall totals in Minneapolis since 1871. <br />Like other convective weather hazards, extreme rainfall goes through more and less active periods. <br />Hennepin County has at times gone many years between major events. 2014, 2002, and 1997, on the <br />other hand, are relatively recent examples of years with multiple extreme events in the county. <br />4.3.6.7. Historical (statistical) data/previous occurrence Bld <br />NOAA Atlas 14 is the definitive source for extreme rainfall estimates and contains the most recent scientific <br />estimates of rainfall amounts for durations from 5 minutes to 60 days, and with recurrence intervals of 1 <br />through 500-years. The following table is for a point selected in central Hennepin County. The top row <br />contains recurrence intervals (or return periods), and the left column is storm durations. The value in bold <br />where they intersect is the likely amount in inches expected for a storm of that duration, at that recurrence <br />interval. The values in parentheses represent the 90% confidence range around the bold value Example: <br />For 24-hour rainfall at a 100-year recurrence interval is estimated to be 7.34 inches, and is 90% likely to <br />be between 5.55, and 9.65 inches. <br />120 <br />