Future climate change projections suggest an increasing frequency of short-duration dry spell events over the northeastern United States. To better understand these types of events, we investigate the top ~10% longest short-duration dry spell events over the region using a novel implementation of large-scale meteorological pattern (LSMP) – based analysis to understand antecedent conditions and characteristics of the dry spell events. These top ~10% longest dry spell events are identified as consecutive dry days (CDDs) lasting twelve days or longer. The 500-hPa stream function anomaly fields for the first twelve days of each event are time-averaged and k-means clustering is applied to isolate the dry spell-related LSMPs.

This approach yields two LSMPs. The first LSMP has a strong, low-pressure anomaly over the Atlantic Ocean, southeast of the region, and is more common in winter and spring, while the second LSMP has strong, high-pressure over east-central North America and is most common during autumn. Over the region, both LSMPs produce negative specific humidity anomalies, negative integrated vapor transport from the north, and subsidence associated with a midlatitude jet stream dipole structure that reinforces upper-level convergence. Subsidence is supported by cold air advection in the first LSMP and the location on the east side of the lower-level high pressure in the second LSMP. Extratropical cyclone storm track density across the region is dramatically reduced during these dry spell events. More (56%) short-duration dry spells occurred during the numerous non-drought months than drought months, however the frequency of dry spells is more than three times greater during drought than non-drought months.

Our results provide improved insight into the large-scale meteorology associated with short-duration dry spells in the northeastern United States, and these results also serve as a necessary first step in improving the prediction of these events on monthly and sub-seasonal timescales, which can help to better inform water management practices in the region.

With time permitting, we will examine any linkages that may exist between short-duration dry spells and low-frequency / remote climate modes, such as the Madden-Julian Oscillation.