Assessment of MODIS as a Data Source for Microburst Prediction

NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) is currently being evaluated as a data source for a multispectral algorithm that currently generates the GOES-11 Imager microburst product. The GOES-11 imager microburst algorithm, as described in Pryor (2009), is a predictive linear model (Caracena and Flueck 1988) based on parameter evaluation and pattern recognition techniques as employed in the severe convective storm forecasting process (Johns and Doswell 1992). At a spatial resolution of 1 km, the MODIS instrument is an improvement over the GOES-11 imager with a resolution of 4 km for the infrared bands. Thus, MODIS should provide better detail in the display of microburst risk. Two downburst events from 2008 will be compared to highlight the improvement in performance of MODIS over GOES-11 imager data. During the afternoon of 8 December 2008, clusters of convective storms developed over eastern New Mexico and western Texas, ahead of an upper-level cyclone. Strong downbursts, produced by the convective storm clusters, occurred in close proximity to elevated GOES-11 imager microburst risk values, as indicated by the GOES-11 product image at 2030 UTC. A comparison between the product images generated with GOES-11 and MODIS data revealed that the MODIS image indicated a stronger signal for microburst potential over western Texas during the afternoon of 8 December.


The images above are a MODIS microburst risk image (top) and corresponding GOES-11 microburst risk image at 2030 UTC 8 December 2008 (bottom) with overlying radar reflectivity data from Lubbock, Texas NEXRAD (LBB) at 2118 UTC. Apparent in the product images are clusters of convective storms over the western Texas Panhandle and over eastern New Mexico that would track eastward over western Texas during the following hour. Associated with the convective storm cluster near the New Mexico border were downburst wind gusts of 50 and 57 knots that were recorded by Plains and Denver City (West Texas) mesonet stations at 2115 UTC. Note that the downburst-producing convective storm near Denver City occurred in close proximity to elevated imager microburst risk values, displayed in the images as a progression from yellow to red shading indicating an increase from moderate to high risk. High downburst risk was more apparent in the MODIS image as a darker orange shading immediately downstream of the convective storm near Denver City. The downbursts were evaporatively initiated (Caracena and Flueck 1988) and resulted in the generation of a dust storm over western Texas that affected the Lubbock area (http://www.mesonet.ttu.edu/cases/DuststormI_120808/Dec-08-2008Duststorm.html).

Below is a comparison of the MODIS microburst risk image at 2035 UTC 9 August 2008 (top) and corresponding GOES-11 microburst risk image at 2130 UTC (bottom) with overlying radar reflectivity data from Phoenix, Arizona NEXRAD (IWA) at 2238 UTC. Apparent in the microburst product images is a convective storm over northern Maricopa County that produced a downburst (46 knot wind gust) at Horseshoe Lake Automated Local Evaluation in Real Time (ALERT) station at 2238 UTC. In a similar manner to the western Texas downbursts of 8 December, the strong downburst occurred in close proximity to a local maximum in risk, as indicated by the orange shading immediately downstream of the convective storm, especially apparent in the MODIS image with 1 km resolution.




Both cases demonstrate the strength of the MODIS-derived microburst risk image in the assessment of downburst potential, especially with evaporatively initiated downbursts. With 1 km spatial resolution, the MODIS image can serve as an example of the capability of future geostationary satellite sensors (i.e. GOES-R) in displaying multispectral derived images, especially images with utility in convective storm nowcasting.

REFERENCES

Caracena, F., and J.A. Flueck, 1988: Classifying and forecasting microburst activity in the Denver area. J. Aircraft, 25, 525-530.

Johns, R.H., and C.A. Doswell, 1992: Severe local storms forecasting. Mon. Wea. Rev., 121, 1134–1151.

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