A climatological analysis of heatbursts in Oklahoma (1994–2009)

Abstract

ABSTRACT:Heatbursts are characterized by a sudden and highly localized increase in air temperature, a simultaneous decrease in relative humidity and dewpoint temperature, and strong gusty winds, typically associated with decaying thunderstorms. The small spatial extent and short duration of most heatbursts makes detailed study of these events difficult using the standard federal observation network (e.g. hourly observations) established in most countries. Thus, many discussions of heatbursts note that they are 'rare' phenomena. However, observations from the Oklahoma Mesonet indicate that although heatbursts are meso-alpha scale phenomena, they are not rare. Using multi-criteria analysis, 207 heatburst events of various magnitudes, areal coverage and duration were identified between 1994 and 2009 across Oklahoma. Significantly more heatbursts were detected in the western two-thirds of the state as compared to the eastern third. Heatbursts were primarily nocturnal events, with 70% of heatburst events initiated between 0000 and 0800 UTC (i.e. between 6 p.m. and 2 a.m. Central Standard Time). With 62 of the 207 events, June was the most active month for heatbursts. At the other extreme, no heatbursts were detected during February and November, and only one was observed during January and December. Almost all of the heatbursts occurred underneath or adjacent to weak radar echoes at the time of the event. Four basic radar patterns were associated with the events: (1) radar echoes associated with rapidly weakening convection, (2) weak reflectivity not produced by or associated with deep moist convection, (3) weak radar echoes to the rear of a dissipating mesoscale convective system (MCS) and (4) weak reflectivity along the periphery of intense convection that did not appear to be weakening.

Mesoscale observations of an extended heat burst and associated wind storm in Central Oklahoma

“…At the same time, a stable layer extended from the surface to approximately 750 hPa. Such profiles were consistent with those noted previously as being conducive toward heat burst formation (Johnson et al, 1983(Johnson et al, , 1989Bernstein and Johnson, 1994;McPherson et al, 2011). Figure 7).…”

“…The results found that heat bursts were most frequently observed in the western two-thirds of the state, were mainly nocturnal events and were most common during the warm season with June as the most active month. McPherson et al (2011) also noted that nearly all of the events occurred in close proximity to weak radar echoes generally less than 30 dBz and yielded an average temperature increase of 5.3°C, an average decrease in dew point temperature of 6.9°C, an average peak wind speed of 18.2 m s −1 , and an average thermodynamic perturbation of 72 min. The results further reinforce that with a mesoscale surface network in place, heat burst events and their evolution can be observed with increased frequency and resolution.…”

“…Bernstein and Johnson (1994) noted that a main contributor to the relative rareness of heat burst events is likely due to the rare occurrence of a shallow stable layer with strong descent above it. Using data from the Oklahoma Mesonet, a dense network of mesoscale observing stations in Oklahoma, McPherson et al (2011) documented and analysed 207 heat burst events captured by the network from 1994 to 2009. The results found that heat bursts were most frequently observed in the western two-thirds of the state, were mainly nocturnal events and were most common during the warm season with June as the most active month.…”

High-Resolution Surface Observations for Climate Monitoring

“…Prior to the analysis of an 18-year record of Oklahoma Mesonet data, less than two dozen heatbursts had been documented worldwide in the scientific literature. With the high-resolution Mesonet observations however, 207 heatburst events 2 of various magnitudes, areal coverage, and duration were identified between 1994 and 2009 across Oklahoma [50]. The geographical distribution of heatbursts across Oklahoma (Fig.…”

“…Geographical distribution of heatburst detections by climate division (CD) across Oklahoma and by month (J, F, M,... for January, February, March,...) from 1 January 1994 to 15 August 2009[50]. If a heatburst event were measured at 10 Oklahoma Mesonet sites, it was counted as 10 detections.…”