MODIS Microburst Product Demonstrates Capability for Forecasting Downburst Potential

During the afternoon of 29 March 2009, strong convective storms developed over the Blue Ridge Mountains of Maryland and West Virginia ahead of cold front. The line of storms tracked through north-central Maryland between 1800 and 2000 UTC, producing strong downburst winds and hail. The mid-afternoon (1810 UTC) Moderate Resolution Imaging Spectroradiometer (MODIS) microburst product image indicated elevated risk values over northern Virginia and central Maryland. Doppler radar indicated convective winds between 35 and 48 knots as the storm line moved through Frederick County, Maryland between 1800 and 2000 UTC. The MODIS microburst algorithm incorporates brightness temperature differences between bands 27 (6.535 - 6.895 μm), 31 (10.780 - 11.280 μm) and 32 (11.770 - 12.270 μm) and is desirable due to its high spatial resolution (1 km).

The image above is a Moderate Resolution Imaging Spectroradiometer (MODIS) derived microburst risk product at 1810 UTC 29 March 2009 with overlying radar reflectivity and radial velocity from Sterling, Virginia NEXRAD (KLWX) at 1904 UTC. The microburst product image displays a convective storm line tracking eastward through Frederick County, Maryland into a region of elevated microburst risk (orange shading) with output brightness temperature difference (BTD) values greater than 40K. Based on previous validation of the GOES-11 imager microburst product (Pryor 2009), output BTD greater than 40K is associated with wind gust potential of greater than 40 knots. Radial velocity values, immediately downstream of the storm line, were indicated to be in the 35 to 48 knot range. At this close range to the radar location, radial velocity can serve as a fair estimate of surface winds, and thus, in the absence of measured surface winds, could be used for verification purposes.



References

Pryor, K.L., 2009: Microburst windspeed potential assessment: progress and developments. Preprints, 16th Conf. on Satellite Meteorology and Oceanography, Phoenix, AZ, Amer. Meteor. Soc.