Section 3 presents the 21 June 2008 case study along with a discussion of the WA04 procedure centered on the case study, followed by a summary and conclusions in section 4.Ī case study of the 21 June 2008 lightning outbreak is presented to demonstrate a procedure that could be used to forecast dry thunderstorm events in the western United States. Section 2 briefly describes the methodology used to diagnose this case including model choice and a description of the indices used. In addition, part of the WA04 procedure did not strongly indicate an outbreak, suggesting the procedure has some limitations. Part of the motivation of this study is to bring this procedure to a wider audience as it could have helped forecasters anticipate the outbreak. Walbrun 2010, personal communication), partly because WA04 focused on the Great Basin. While the WA04 procedure was available at the time of the 21 June 2008 outbreak, it saw very limited us among western United States National Weather Service Forecast Offices (M. In this study, a hybrid forecasting tool combining the WA04 and MI04 procedures will be used to investigate the 21–22 June lightning outbreak. ( Table 1 lists all the acronyms used in the text in order of their appearance.) The high-level total totals index (HLTT) developed by Milne (2004, hereafter MI04) was also used in the WA04 procedure to address the mid- to upper-level instability. Wallmann (2004, hereafter WA04) presented one such procedure where the potential vorticity and upper-level lapse rates were associated with thunderstorm outbreaks in the western United States. It is therefore imperative to develop a forecast framework for dry thunderstorms that will aid forecasters and provide a subjective complement to the objective tools. Finally, the development of experimental probabilistic lightning products ( Bothwell 2005, 2008) adds another objective tool used in forecasting dry thunderstorms.ĭespite the advancement of objective forecast tools for forecasting dry thunderstorms in recent years, large events such as the June 2008 California outbreak continue to be missed or poorly forecast. In addition, more recent research has investigated not only the thermodynamic parameters required for instability, but also the low-level environment conducive for evaporating much of the rainfall before it reaches the ground ( Rorig et al. Rorig and Ferguson (1999) investigated the thermodynamic parameters involved with dry lightning outbreaks and the probability that thunderstorms will be dry. Recent years have seen a greater emphasis on research to effectively forecast dry thunderstorms. Therefore, much of this paper will be devoted toward California where the impacts were greatest. However, the level of vegetation moisture was considerably higher over much of Oregon compared to California and no large fires were recorded as a result of this event. As large as this event was, it could have been larger as a significant amount of lightning also occurred in Oregon. Large numbers of firefighting resources from across the United States were sent to California as a result of this outbreak and remained committed well into August, which put a huge strain on the national firefighting system. 1), where several large fires are grouped together by proximity and jurisdiction.ĭue to the enormous scale of this event, several hundred fires remained unstaffed on the morning of 22 June 2008. By late evening on 21 June, over 1500 new lightning-caused fires were started, eventually resulting in numerous large fire complexes ( Fig. In fact, no fire weather watches or red flag warnings were issued for the area until copious amounts of lightning were already observed. Fires are much more likely to be controlled during the early stages and, therefore, would cost much less to fight.Īlthough isolated thunderstorms were forecast over portions of northern California as much as 60 h in advance, the severity of the 21–22 June 2008 California lightning outbreak was not well forecast. Forecasting these events in advance, even just 24–48 h, would significantly help fire agencies preposition firefighting resources in anticipation of a large outbreak. These extreme events put a huge strain on local initial fire suppression efforts (“initial attack”), and many fires often go unstaffed due to the lack of available fire personnel. In the largest lightning outbreaks, hundreds of new fires may be started in a 24–36-h period. Dry thunderstorms are responsible for starting thousands of wildland fires every year. of rainfall, for the western United States has long been a problem. Forecasting “dry” thunderstorms, traditionally those storms that produce less than 2.5 mm or 0.1 in.
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