New Results of Microburst Product Comparison Study

A cross-comparison of the Geostationary Operational Environmental Satellite (GOES) Microburst Windspeed Potential Index (MWPI) to the Haines Index that characterizes the potential impact of dry, unstable air on wildfire behavior and growth is currently in progress. During the afternoon of 23 June 2010, strong convective storms developed ahead of an upper-level disturbance over New Mexico and then tracked eastward into the western Texas Panhandle region. Convective storms produced numerous downbursts over western Texas during the evening hours of 23 June. Both the 2300 UTC GOES Microburst Windspeed Potential Index (MWPI) and Rapid Update Cycle (RUC) model-derived Haines Index products effectively indicated the potential for strong downbursts about three to four hours prior to each event. Large convective available potential energy (CAPE) and a steep temperature lapse rate, especially below the 700-mb level, were forcing factors for strong convective downdrafts.

Figure 1. Geostationary Operational Environmental Satellite (GOES) Microburst Windspeed Potential Index (MWPI) product image at 2300 UTC 23 June 2010.

Figure 2. Haines Index product based on the Rapid Update Cycle (RUC) model analysis valid at 2300 UTC with overlying radar reflectivity at 0224 UTC 24 June (bottom). White crosses mark the location of Friona (FAS) and Dimmitt (DMS) West Texas Mesonet stations.

Figure 3. Geostationary Operational Environmental Satellite (GOES) sounding profile from Eunice, Texas (near Dimmitt) at 2300 UTC 23 June 2010.

Figure 1 shows that the 2300 UTC Geostationary Operational Environmental Satellite (GOES) Microburst Windspeed Potential Index (MWPI) product image indicated a local maximum in values downstream of developing convective storms over New Mexico that would eventually track into western Texas after 0000 UTC 24 June. The corresponding GOES sounding profile in Figure 3 at Eunice, Texas displays a favorable classic “inverted V” profile that prevailed over western Texas near the maximum in MWPI values. A deep dry adiabatic lapse rate (DALR) layer below the 700-mb level and a dry subcloud layer fostered intense downdraft development due to evaporational cooling and the resulting downburst winds. The Rapid Update Cycle (RUC) model-derived Haines Index product in Figure 2 was generated and visualized by Man computer Interactive Data Access System (McIDAS)-V. A vertical temperature difference (between 850 and 700-mb levels) greater than 15°C (dark orange shading) and a dewpoint depression greater than 25°C yielded a Haines Index value of six (6) in the vicinity of Dimmitt and Friona, Texas, the highest for the index. Consequently, this index echoed favorable conditions for strong downbursts as presented in the MWPI image. Downburst wind gusts of 40 knots and 54 knots were recorded at Dimmitt and Friona West Texas Mesonet station, respectively, between 0200 and 0300 UTC 24 June. This case shows tremendous potential for the Haines Index, originally conceived as a wildfire threat product, in downburst potential assessment.