Subseasonal Predictability of US Heat Waves/Droughts Associated with Planetary Wave Events

In this proposed project, we focus on summertime droughts and associated heat waves that last for 5 days to about 2 weeks over the continental US. Our overall goal is to investigate the prospects for predicting the likelihood of these events as a result of their connections with intraseasonal fluctuations in the midlatitude planetary waves and the potential for predicting those fluctuations.

Prospects for predicting droughts and heat waves based on their connections to intraseasonal planetary wave variations may not seem promising. After all, typical instantaneous states are unpredictable after about 10 days due to the chaotic nature of the atmosphere. This fact, however, does not preclude the possibility that time-averaged, forced or unusually predictable patterns could be predictable on longer time scales. Until now, the search for sources of intraseasonal predictability has primarily focused on atmospheric phenomena driven by Madden-Julian Oscillation (MJO) or Asian summer monsoons, or by boundary conditions including sea surface temperature and soil moisture. But our recent study based on a 12,000-year integration of an atmospheric general circulation model found that a midlatitude planetary wave pattern that features a zonal wavenumber-5 structure can enhance probability forecasts of US heat waves/droughts up to 15-20 days ahead. Since that analysis found internal midlatitude dynamics is primarily responsible for this pattern, those results open up a new possibility for predicting the likelihood of US droughts and heat waves.

Here we seek support to build on this promising result. The primary purposes include: (a) confirming the robustness of the result by repeating analysis for other models and reanalysis fields and determining whether more than one atmospheric pattern may give predictability of droughts and heat waves, (b) elucidating certain processes (boundary conditions or remote heating) might enhance the predictability of the heat waves/droughts we found, (c) assessing whether the predictability we found is properly represented in National Multi-model Ensemble (NMME) phase II models, and (d) transferring our knowledge to a framework suitable for operational predictions.

By performing our analysis, relating it to NMME forecasts and adapting it to operational settings, this proposal targets priorities of the MAPP program solicitation: (a) research to advance understanding, monitoring, and prediction of drought and (b) research to advance NOAA’s operational systems for climate prediction. Also, all activities are tightly related to the NOAA Next-Generation Strategic Plan (NGSP) objectives of “improving scientific understanding of the changing climate system and its impacts” and “climate mitigation and adaptation”.