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Table 2-1 Climate and Precipitation Data
<br />January
<br />13.9
<br />III I�� I IIII III�IIIIIIII� o
<br />1111111 111111
<br />IIIIIIIIIIII
<br />up
<br />12.4
<br />12
<br />ii illilillililllMI
<br />0000000000l0000000000000000000000000000000lu, II
<br />1111111111111
<br />IIIII. �lilu
<br />0.60
<br />11 01,1,1,1,1,11111,1,1,1,1,11111,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,11 .11211111111111:01„,
<br />111111111101111 III IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII
<br />'l it1111
<br />0.83
<br />February
<br />19.2
<br />15.2
<br />1.15
<br />0.71
<br />March
<br />31.4
<br />30.4
<br />1.41
<br />1.71
<br />April
<br />46.4
<br />42.9
<br />3.30
<br />2.75
<br />May
<br />58.1
<br />56.9
<br />5.23
<br />3.60
<br />June
<br />66.3
<br />66.9
<br />4.72
<br />4.36
<br />July
<br />70.9
<br />71.9
<br />4.88
<br />3.92
<br />August
<br />68.6
<br />68.8
<br />3.98
<br />4.22
<br />September
<br />60.2
<br />61.2
<br />3.18
<br />3.50
<br />October
<br />47.7
<br />47.1
<br />2.85
<br />2.57
<br />November
<br />32.2
<br />31.3
<br />1.50
<br />1.77
<br />December
<br />18
<br />19.4
<br />1.51
<br />1.07
<br />Total
<br />44.4
<br />43.6
<br />31.01
<br />34.31
<br />Source: Minnesota Climatology Working Group gridded precipitation dataset (precipitation); NOAA normal
<br />summaries, Cedar, MN station (1981-2010 temperature); NWS, Andover 1N station (2010-2019
<br />temperature)
<br />The amount, rate, and type of precipitation are important in determining flood levels and stormwater
<br />runoff rates. While average weather poses little risk to human health and property, extreme precipitation
<br />events may result in flooding that threatens infrastructure and public safety. NOAA published Atlas 14,
<br />Volume 8, in 2013. Atlas 14 is the primary source of information regarding rainfall amounts and frequency
<br />in Minnesota. Atlas 14 provides estimates of precipitation depth (i.e., total rainfall in inches) and intensity
<br />(i.e., depth of rainfall over a specified period) for durations from 5 minutes up to 60 days. Atlas 14
<br />supersedes publications Technical Paper 40 (TP-40) and Technical Paper 49 (TP-49) issued by the National
<br />Weather Bureau (now the National Weather Service) in 1961 and 1964, respectively. Atlas 14
<br />improvements in precipitation estimates include denser data networks, longer (and more recent) periods
<br />of record, application of regional frequency analysis, and new techniques in spatial interpolation and
<br />mapping. Comparison of precipitation depths between TP-40 and Atlas 14 indicates increased
<br />precipitation depths for more extreme (i.e., less frequent) events. Table 2-2 lists selected rainfall events for
<br />the District.
<br />Runoff from spring snowmelt is not provided in Atlas 14 and current regional snowmelt runoff data is not
<br />available (Minnesota Stormwater Manual, 2019). However, snowmelt and rainstorms occurring during
<br />snowmelt in early spring are significant in this region. The volumes of runoff generated, although they
<br />2-2
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