New GOES Sounder Microburst Product Demonstrates Effectiveness

An unusual April heat wave over the Mid-Atlantic region fostered favorable conditions for isolated afternoon convective storms. During the afternoon of 26 April 2009, isolated convective storms developed over the Blue Ridge Mountains of Virginia as a result of strong solar heating of the mountain ridges. Convective storm activity then tracked northeastward into the western piedmont. A convective storm produced a strong downburst that was observed at an airport near Charlottesville, Virginia at 2024 UTC. Elevated index values were indicated by the new Geostationary Operational Environmental Satellite (GOES) sounder microburst product in proximity to Charlottesville Airport less than two hours prior (1900 UTC) to the observed downburst. Similar to the GOES imager microburst product (Pryor 2009), the sounder microburst algorithm employs brightness temperature differences (BTD) between band 11 (Midlevel level water vapor, 7.0μm), band 8 (longwave infrared window, 11μm), and split window band 7 (12μm). Based on previous research using GOES imager data over the western United States, it was found that BTDs, using satellite sensor bands near these wavelengths, produced a strong signal for downburst potential. Moderate Resolution Imaging Spectroradiometer (MODIS) data was also available during the time period of convective storm initiation and provided a strong indication of downburst potential as well.

The images above are a Geostationary Operational Environmental Satellite (GOES) sounder microburst product at 1846 UTC (top) and a MODIS microburst product at 1835 UTC 26 April 2009 with overlying radar reflectivity imagery from Sterling, Virginia NEXRAD (KLWX). The microburst product images display convective storm activity developing over the Blue Ridge Mountains of Virginia that would track northeastward into the western piedmont during the following one to two hours. The MODIS image indicated higher downburst potential over most of Maryland and Virginia with lower values over the Chesapeake Bay where the boundary layer was more stable due to the cooler water surface temperatures. Overlying radar reflectivity imagery displayed the area of convective storms over Albemarle County moving northeast near Charlottesville. A convective storm produced a strong downburst (wind gust 40 knots) that was observed at Charlottesville Airport at 2024 UTC. The parent storm exhibited high reflectivity (>50 dBZ) and a bow echo signature typically associated with downbursts (Przybylinski 1995) in which the apex of the bow was over the airport. Elevated output BTD greater than 40K were indicated by both the GOES and MODIS microburst products in proximity to the downburst less than two hours prior to downburst occurrence. Previous validation has identified that BTD greater than 40K is strongly correlated to wind gust potential of 40 knots or greater. The microburst products and the 1900 UTC Rapid Update Cycle (RUC) model analysis sounding profile displayed below show that the preconvective environment over the Virginia piedmont region was more typical of the Great Plains region during the summer with a steep temperature lapse rate and a well-mixed boundary layer that favored the development of intense convective downdrafts and resultant downburst generation. The sounding profile can be readily identified as an "inverted V" profile that is typical for the High Plains and interior western U.S.

The above image is an example of the web version of the GOES sounder microburst product. The image displays moderate microburst risk in proximity to the Charlottesville downburst (40 knots, plotted in image). The GOES-East sounder microburst product image and an animation are available on the GOES microburst product web page.

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.

Przybylinski, R.W., 1995: The bow echo. Observations, numerical simulations, and severe weather detection methods. Wea. Forecasting, 10, 203-218.

GOES Microburst Product Web Page Improvements

Improvements to selected Geostationary Operational Environmental Satellite (GOES) microburst product web pages have been implemented. Improvements include implementation of AnimationS (AniS) software, a general-purpose Java image animator tool for websites developed by University of Wisconsin Space Science and Engineering Center (SSEC). The software allows simple animation of two or more images with the following functions: stop and start animation, set animation speed, single step frames, change direction of animation sequence, go directly to the first or last frame, and movie looping or "rocking" modes. These improvements have been implemented on the GOES imager microburst product page:

http://www.star.nesdis.noaa.gov/smcd/opdb/kpryor/mburst/mbimg.html

and the GOES sounder Microburst Windspeed Potential Index (MWPI) product page:

http://www.star.nesdis.noaa.gov/smcd/opdb/kpryor/mburst/mwpi.html.

The image below is an example of AniS software as implemented on

the GOES imager microburst product web page: 

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.