Dynamical analysis of extreme precipitation in the US northeast based on large-scale meteorological patterns

Abstract

25Previous work has identified six Large-Scale Meteorological Patterns (LSMPs) of 26 dynamic tropopause height associated with extreme precipitation over the Northeast US, with 27 extreme precipitation defined as the top one percent of daily station precipitation. Here, we 28 examine the three-dimensional structure of the tropopause LSMPs in terms of circulation and 29 factors relevant to precipitation, including moisture, stability, and synoptic mechanisms 30 associated with lifting. Within each pattern, the link between the different factors and extreme 31 precipitation is further investigated by comparing the relative strength of the factors between 32 days with and without the occurrence of extreme precipitation. 33The six tropopause LSMPs include two ridge patterns, two eastern US troughs, and two 34 troughs centered over the Ohio Valley, with a strong seasonality associated with each pattern. 35Extreme precipitation in the ridge patterns is associated with both convective mechanisms 36 (instability combined with moisture transport from the Great Lakes and Western Atlantic) and 37 synoptic forcing related to Great Lakes storm tracks and embedded shortwaves. Extreme 38 precipitation associated with eastern US troughs involves intense southerly moisture transport 39 and strong quasi-geostrophic forcing of vertical velocity. Ohio Valley troughs are associated 40 with warm fronts and intense warm conveyor belts that deliver large amounts of moisture ahead 41 of storms, but little direct quasi-geostrophic forcing. Factors that show the largest difference 42 between days with and without extreme precipitation include integrated moisture transport, low-43 level moisture convergence, warm conveyor belts, and quasi-geostrophic forcing, with the 44 relative importance varying between patterns. 45

North American extreme precipitation events and related large-scale meteorological patterns: a review of statistical methods, dynamics, modeling, and trends

“…Extreme description Agel et al (2017Agel et al ( , 2019 Top 1% of precipitating days Bradley and Smith (1994) At least 12.5 mm at a station in 24 h, with a greater than 25 mm average over 12,500 km 2 Ely et al (1994) Flood-producing rain events Groisman et al (2005) Daily thresholds 90-99.9%, area averaged Grotjahn and Faure (2008) 24 + hour precipitation exceeding 63.5 mm total or 50.8 mm day −1 Hamada et al (2015) Effective radar reflectivity pixels with maximum near-surface rainfall rate or maximum 40-dBZ echo-top height Higgins et al (2000a) 25 largest 3-day precipitation events Keim (1996) 2-day totals of 76.2 mm (3″) or more Kharin et al (2013) Annual daily maximum Kunkel et al (2012) Daily precipitation exceeding 5-year recurrence interval Kunkel et al (2013) Station-specific 97th percentile Lackmann and Gyakum (1999) Flood-producing rain events LaPenta et al (1995) Three largest floods 1860-1989Maddox et al (1979, 1980 NOAA flash flooding reports Milrad et al (2010a, b) Median extreme 2-day precipitation exceeding 33.78 mm Milrad et al (2014) Top 10% 1-3 day precipitation Min et al (2011) Annual 1-and 5-day maximum precipitation (Rx1 day, Rx5 day) Moore et al (2012) 48-h precipitation exceeding 1000-year recurrence interval Moore et al (2015) 99th and 99.9th percentiles of daily precipitation, plus areal extent above median size Schumacher and Johnson (2005) Daily precipitation exceeding 50-year recurrence interval Sillmann et al (2013a) Various ETCCDI indices Toredi et al (2013) P90 (daily 90th percentile) Warner et al (2012) Top 50 48-h station precipitation Westra et al (2013) Annual daily maximum Zhang et al (2010) Annual winter maximum, + 2nd and 3rd maxima…”

“…These multiple-LSMP studies have focused on several different geographic regions within North America: Maddox et al (1979) and Kunkel et al (2012) considered the coterminous US, while Bradley and Smith (1994) considered the southern plains; LaPenta et al (1995), the NWS Eastern Region; Keim (1996), the southeastern US; Schumacher and Johnson (2005), the eastern US; Milrad et al (2010a, b), St. John's, Newfoundland; Milrad et al (2014), Montreal, Canada; Moore et al (2015), the southeastern US; and Collow et al (2016) and Agel et al (2017Agel et al ( , 2019, the northeastern US. The results are somewhat difficult to directly compare, due not only to the different geographic regions, but also to considerable differences in the definition used to identify extreme precipitation events, the period considered, and the methodology used.…”

“…Most of these studies have focused on analyzing the LSMPs occurring contemporaneously with extreme precipitation, with less emphasis on testing the causal nature of the identified relationships. As one approach to addressing this, Agel et al (2019) compared the strength of different factors within the same LSMP between days with extreme precipitation and days without extreme precipitation for the Northeast US, with the largest difference occurring in integrated moisture transport, low-level moisture convergence, occurrence of warm conveyor belts, and quasi-geostrophic forcing, with the relative importance varying between patterns.…”

“…8;Milrad et al 2014), and the relationship between the dynamic tropopause (Agel et al 2017) and multiple precipitation factors ( Fig. 9; Agel et al 2019).…”

“…Fig. 9 The six extreme precipitation LSMPs identified for the Northeast US in Agel et al (2017Agel et al ( , 2019, shown in terms of a tropopause pressure (Agel et al 2019, Fig . 1a), and b associated mechanisms (Agel et al 2019, Fig.…”