Seasonal Noise Versus Subseasonal Signal: Forecasts of California Precipitation During the Unusual Winters of 2015–2016 and 2016–2017

Abstract

Subseasonal forecasts of California precipitation during the unusual winters of 2015–2016 and 2016–2017 are examined in this study. It is shown that two different ensemble forecast systems were able to predict monthly precipitation anomalies in California during these periods with some skill in forecasts initialized near or at the start of the month. The unexpected anomalies in February 2016, as well as in January and February 2017, were associated with shifts in the position of the jet stream over the northeast Pacific in a manner broadly consistent with associations found in larger ensembles of forecasts. These results support the broader notion that what is unpredictable atmospheric noise at the seasonal time scale can become predictable signal at the subseasonal time scale, despite that the lead times and verification averaging times associated with these forecasts are outside the predictability horizons of canonical midrange weather forecasting.

Microclimate–forage growth linkages across two strongly contrasting precipitation years in a Mediterranean catchment

“…Enhancing seasonal weather forecast skill and future climate projection accuracy are an active area of research (Singh, Ting, Scaife, & Martin, 2018;Wang, Anichowski, Tippett, & Sobel, 2017) that should lead to improved capabilities to provide seasonal outlooks and longer term prediction of forage production.…”

California's Drought of the Future: A Midcentury Recreation of the Exceptional Conditions of 2012–2017

“…The first year of abnormal drought conditions was WY2014, characterized by record-high dryness driven by what is now colloquially referred to as the Ridiculously Resilient Ridge, a region of anomalously persistent blocking that redirected atmospheric moisture northward and led to record-high precipitation through the Pacific Northwest and Alaska (Swain et al, 2014). However, the El Niño that emerged was unusual as it actually enhanced total precipitation in Northern California instead, as a consequence of a northward shifted and intensified storm track that accompanied a positive geopotential height anomaly off the California coast (Paek et al, 2017;Wang et al, 2017). Consequently, the Palmer Drought Severity Index (PDSI; Palmer, 1965), a commonly employed mechanism for monitoring drought intensity, reaching a record-low value of −7.01 in July 2014, indicative of extraordinary drought conditions.…”

Zonal Wind Indices to Reconstruct CONUS Winter Precipitation

“…While we find no secular trends in the historic record of PC1, the behavior of PC1 under anthropogenic warming should be assessed. An exploration of the predictability of the wind indices by coupled general circulation models at subseasonal timescales, including how predictability depends on Madden‐Julian Oscillation amplitude and phase . There is recent evidence that subseasonal precipitation forecasts may have skill where seasonal forecasting models err (Wang et al, ). Our preliminary results (not shown) indicate that strong relationships between PC1 and CONUS precipitation are present at pentad timescales.…”