Two Large-Scale Meteorological Patterns Are Associated with Short-Duration Dry Spells in the Northeastern United States, Part I: General Properties

<strong>Description</strong> The zip file contains folders with processed data from the ERA5 dataset for some of the atmospheric fields considered in this study. Original (pre-processed) ERA5 data (Hersbach et al. 2020) is available at https://cds.climate.copernicus.eu/#!/search?text=ERA5&amp;type=dataset. For each processed data file (netCDF format), the time steps correspond with the events and numerical order as listed in Table S1 of the Supplemental Materials for this article. <strong>Abstract</strong> Short-duration dry spell events over the northeastern United States are grouped into two types based on the temporal and spatial evolution of the large-scale meteorological patterns (LSMPs) during the onset period of the events. These events are first identified as consecutive dry day (CDD) events lasting nine days or longer. The 500-hPa stream function anomaly fields for the first nine days of each respective event are time-averaged, and <em>k</em>-means clustering is applied in order to isolate the dry spell-related LSMPs. The first cluster is associated with a strong, low-pressure area over the Atlantic Ocean, southeast of the region. The second cluster is defined by a strong, high-pressure centered over east-central North America. Wave activity flux convergence is consistent with the development of the first cluster LSMP, and less apparent for the second cluster LSMP. Both clusters have negative specific humidity anomalies, changes to normal integrated vapor transport, and subsidence associated with a dipole structure in the midlatitude jet stream that generates upper-level convergence. Subsidence is supported in the first cluster by cold air advection into the region, while sinking motion occurs primarily from the high-pressure area in the second cluster. Extratropical cyclone storm track density across the Northeast is dramatically reduced during the dry spell events. The connection between drought months and short-duration dry spells is briefly examined, and reveals that most short-duration dry spells occur in neither drought nor pluvial months, indicating that these events tend to occur abruptly and disrupt normal precipitation conditions.