This study examines U.S. Northeast daily precipitation and extreme precipitation characteristics for the 1979–2008 period, focusing on daily station data. Seasonal and spatial distribution, time scale, and relation to large-scale factors are examined. Both parametric and nonparametric extreme definitions are considered, and the top 1% of wet days is chosen as a balance between sample size and emphasis on tail distribution. The seasonal cycle of daily precipitation exhibits two distinct subregions: inland stations characterized by frequent precipitation that peaks in summer and coastal stations characterized by less frequent but more intense precipitation that peaks in late spring as well as early fall. For both subregions, the frequency of extreme precipitation is greatest in the warm season, while the intensity of extreme precipitation shows no distinct seasonal cycle. The majority of Northeast precipitation occurs as isolated 1-day events, while most extreme precipitation occurs on a single day embedded in 2–5-day precipitation events. On these extreme days, examination of hourly data shows that 3 h or less account for approximately 50% of daily accumulation. Northeast station precipitation extremes are not particularly spatially cohesive: over 50% of extreme events occur at single stations only, and 90% occur at only 1–3 stations concurrently. The majority of extreme days (75%–100%) are related to extratropical storms, except during September, when more than 50% of extremes are related to tropical storms. Storm tracks on extreme days are farther southwest and more clustered than for all storm-related precipitation days.

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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

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The boreal winter response to tropical convection in the eastern Indian Ocean is investigated by increasing the mid‐level diabatic heating for that region in the NCAR Community Atmosphere Model, version 3.1. The response is quite similar to the analytic Gill solution to steady heating, with a pair of Rossby wave packets poleward and to the west of the heating, extending into mid‐latitudes, and a Kelvin response to the east of the heating. Changes to tropical convection in the eastern Indian Ocean are an important component of several important modes of atmospheric variability, including the Madden‐Julian Oscillation, some El Niño‐Southern Oscillation events, and the Indian Ocean Dipole. The simulated response has considerable similarities to observational aspects of these modes, both in terms of the Gill‐like circulation patterns and changes to precipitation over Southwest Asia, demonstrating the central importance of the Indian Ocean convection in determining the regional response.