VISIT: Meteorological Interpretation Blog

he VISIT lesson “Forecasting Convective Downburst Potential Using GOES Sounder Derived Products” presents current applications of a suite of GOES sounder-derived products. The lesson has been recently revised to include updated imagery examples, and new case studies of downburst events that occurred over the United States Great Plains during June and August 2009. The cases demonstrated the effectiveness of coordinated use of the GOES Microburst products in evolving convective storm environments.  The objective of the lesson is to provide better understanding of techniques for predicting the risk of convective downbursts utilizing GOES sounder derived data.  The guide for the lesson is available at the following web address:  http://www.cira.colostate.edu/ramm/visit/downburst.html .  Also revised is the audio playback version of the lesson, also available on the student guide page.  An example of one of the case studies of a significant downburst event is summarized below. 

During the afternoon of 26 August 2009, strong convective storms developed along a weak, slow-moving cold front as it was tracking eastward over Oklahoma. Although there was very little temperature contrast across the front, the front acted as a convergence zone and a trigger for deep, moist convection. The pre-convective environment downstream of the cold front over western Oklahoma was dominated by vertical mixing that fostered the development and evolution of a convective boundary layer. Elevated Geostationary Operational Environmental Satellite (GOES) imager brightness temperature difference (BTD) values (yellow to orange shading) and Microburst Windspeed Potential Index (MWPI) values in the vicinity of downburst occurrence over western Oklahoma served as evidence of the presence of a well-developed mixed layer. Strong downbursts that were recorded by Oklahoma Mesonet stations between 0000 and 0100 UTC 27 August resulted from a combination of precipitation loading and sub-cloud evaporation of precipitation. These downbursts occurred in proximity to moderate to high microburst risk values as indicated in the 2200 UTC GOES microburst products.

The images above are a Geostationary Operational Environmental Satellite (GOES) imager microburst product at 2200 UTC 26 August 2009(top) and a corresponding GOES sounder Microburst Windspeed Potential Index (MWPI) product (bottom), with the location of Oklahoma mesonet observations (i.e BESS, WEAT, etc.) of downburst wind gusts plotted on the MWPI image. Both product images displayed convective storms developing along the cold front over western Oklahoma. Convective storm activity increased in coverage near the cold front during the following three hours. Downburst wind gusts between 41 and 56 knots were recorded by the Oklahoma Mesonet stations plotted in the MWPI image above between 0000 and 0100 UTC 27 August.
The following are significant downbursts recorded by the Oklahoma Mesonet during this event:
Station - Time (UTC) - Wind Gust (knots)
Bessie - 0005- 50
Kingfisher - 0020 - 43
Weatherford - 0030 - 41
El Reno - 0040 - 50
Medford- 0055 – 56 Also important to note the general increase in MWPI values from southwest (BESS) to northeast (MEDF) associated with a progression from hybrid to stronger wet type downbursts. Downbursts over western Oklahoma were predominantly “hybrid” type, while over north-central Oklahoma (MEDF, BREC), downbursts were “wet” type associated with heavy rainfall.

A convectively active late winter season over the Great Plains has proven fruitful for the assessment of the GOES-11 imager microburst risk product. During the evening of 8 February 2009, a line of convective storms tracked through eastern New Mexico and western Texas, producing several strong downbursts west of Lubbock. This event served as another good example of the utility of the GOES‐West (GOES‐11) imager microburst algorithm described in the previous blog entry (“Forecasting Convective Downburst Potential”, 29 January 2009). This downburst event occurred at the end of a day of boundary layer mixing due to a combination of strong surface heating and low-level wind shear, and thus, demonstrated the importance of the evolution of the convective mixed layer in downburst generation as reflected in the GOES microburst product imagery. The line of convective storms crossed the New Mexico border into Texas around 0100 UTC 9 February. The first downburst recorded in Texas was observed at Denver City West Texas Mesonet station with a wind gust of 47 knots at 0100 UTC, followed by a stronger downburst with a wind gust of 60 knots at 0125 UTC. Further downburst activity was observed at Anton (50 knots) and Reese Center (46 knots) mesonet stations west of Lubbock at 0225 UTC and 0235 UTC, respectively.

The image above is a recent example of the GOES‐11 imager microburst risk product at 0000 UTC 9 February 2009 with overlying radar reflectivity imagery from Lubbock (KLBB) NEXRAD at the time of downburst occurrence at Denver City, 0100 UTC. The product image was visualized by McIDAS-V software, available online at http://www.ssec.wisc.edu/mcidas/software/v/. The image was filtered to display only reflectivity higher than 35 dBZ to emphasize the heaviest precipitation cores where downbursts are likely to be generated. Apparent in the product image is the storm line crossing the Texas border, propagating into a region of high microburst probability as indicated by the progression from orange and red shading in the image. Clouds are represented by light to dark blue shaded areas in the product image. The next product image, valid at 0030 UTC with overlying radar reflectivity imagery at the time of downburst occurrence, shows the eastward progression of the storm line. 0221 UTC radar reflectivity data indicated a small bowing segment of the line northwest of Lubbock (L), associated with the downburst in progress at Anton.

The VISIT lesson “Forecasting Convective Downburst Potential Using GOES Sounder Derived Products” presents current applications of a suite of GOES sounder-derived products. A recent concern pertaining to the GOES sounder products is the current temporal and spatial resolution (60 minutes, 10 km). The GOES-R Advanced Baseline Imager (ABI) has promising capability as a sounder with greatly improved temporal and spatial resolution as compared to the existing GOES (8-P) sounders. However, until GOES-R soundings and associated derived products are operational, a need has been established for a higher resolution GOES-derived microburst risk product. Accordingly, a multispectral GOES imager product has been developed and experimentally implemented to assess downburst potential over the western United States with improved temporal and spatial resolution. The availability of the split-window channel in the GOES-11 imager allows for the inference of boundary layer moisture content. The experimental product is available on the web:

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

The June 2008 copy of “The Front” newsletter highlights upcoming changes to the new Terminal Aerodrome Forecast (TAF) which is scheduled to go operational this November (2008).  See this site: www.weather.gov/os/aviation/taf_testbed.shtml for more information. 

And speaking of TAFs, want to know just what happens to those TAFs you write?  Just what do the Center Weather Service Units (CWSU)s, Air Traffic Control Centers (ARTCC)s, and the airports themselves do with those forecasts? Well, they turn them into valuable graphical displays that help reduce weather related airspace congestion, that’s what.  See the story starting on page three.  For a good “live” example, click here. 

Finally, this season’s newsletter ends with a bit of research coming from the Aviation Weather Center (AWC) regarding the prediction of thunderstorm movement throughout the seasons.  More than 27,000 Convective SIGMETs were analyzed for this study whose details begin on page ten.  Good way to categorize and address the “climatology” of thunderstorms in your area throughout the year. 

(Courtesy NASA/MODIS/TERRA - July 26, 2008)

Currently, California has 26 fire incidents…mostly across the northern half of the state.  Fourteen of these fires are considered large at the moment (= or > 100 acres…see following map).

To date (this fire season - through July 30, 2008), over 750,000 acres of California have burned. Most of the current fires started as a result of lightning strikes between June 20th and June 28th…with a couple of them going back to the last week in May!  Several thousand firefighters from across the country have been deployed to the region over the last couple of months, with additional fire specialists from Canada, Australia, and New Zealand also helping out.  Many Incident Meteorologists are also working these fires this summer.  Check out this recent visible image loop that shows the region between the evening of July 29th and through the morning of the 30th. For more information on these fires as well as others across the country, please go to these sites:  http://gacc.nifc.gov/oncc/, http://www.nifc.gov/, and http://www.inciweb.org/ .