The Great 2006 Heat Wave over California and Nevada: Signal of an Increasing Trend

Abstract

Most of the great California–Nevada heat waves can be classified into primarily daytime or nighttime events depending on whether atmospheric conditions are dry or humid. A rash of nighttime-accentuated events in the last decade was punctuated by an unusually intense case in July 2006, which was the largest heat wave on record (1948–2006). Generally, there is a positive trend in heat wave activity over the entire region that is expressed most strongly and clearly in nighttime rather than daytime temperature extremes. This trend in nighttime heat wave activity has intensified markedly since the 1980s and especially since 2000. The two most recent nighttime heat waves were also strongly expressed in extreme daytime temperatures. Circulations associated with great regional heat waves advect hot air into the region. This air can be dry or moist, depending on whether a moisture source is available, causing heat waves to be expressed preferentially during day or night. A remote moisture source centered within a marine region west of Baja California has been increasing in prominence because of gradual sea surface warming and a related increase in atmospheric humidity. Adding to the very strong synoptic dynamics during the 2006 heat wave were a prolonged stream of moisture from this southwestern source and, despite the heightened humidity, an environment in which afternoon convection was suppressed, keeping cloudiness low and daytime temperatures high. The relative contributions of these factors and possible relations to global warming are discussed.

Real-time weather forecasting in the Western Mediterranean Basin: An application of the RAMS model

“…In addition, the results reproduced in the present paper are analogous to those found in other Mediterranean Regions, using the RAMS model (Pasqui et al, 2004;Federico, 2011), and using other real-time mesoscale models (Bartzokas et al, 2010). Likewise, considering other areas with Mediterranean-type climate regimes, it has been found that atmospheric humidity is the main cause of elevated minimum temperatures in the summer (Gershunov et al, 2009). In contrast, taking into account the temperature field within this season of the year, a cold bias was identified in RAMS simulations over east-central Florida (Case et al, 2002).…”

Climate change, climate justice and the application of probabilistic event attribution to summer heat extremes in the California Central Valley

“…Unlike in AF1, in the AF2 and Natural experiments, daily maximum and minimum temperature were archived for each day of the year, which permited the calculation of Tmin_hi; this is advantageous for the analysis given its increased role in recent heat extremes (Gershunov et al 2009). AF1 has 5-day intervals of specific humidity, allowing for analysis of WBGT in the supplementary materials.…”

“…1). This domain is chosen because of its general spatial coherence in terms of its summer climatology at lower elevations and because it has been analyzed extensively in the literature (Gershunov et al 2009;Walsh et al 2014). Decadal anomalies are calculated as the differences from the mean over the period 1901-1960. The CA/NV domain's JJA Tmax_hi (Fig.…”

“…However, we did not screen years based on tropical Pacific SSTs because major heat waves have occurred during all phases of the El Niño-Southern Oscillation (see Gershunov et al 2009). …”

“…In California's Central Valley, heat waves have become progressively more severe in recent decades due to higher humidity and warmer nighttime temperatures (Gershunov et al 2009). For example, a particularly severe heat wave in 2006 was linked with increases in emergency department visits and hospitalizations (Knowlton et al 2009) and at least 146 deaths (California Department of Health Services 2007).…”