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.

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. 

Volcanoes, particularly volcanic ash, are major concerns to many of us in meteorology.  While the physical presence of the mountain and the energy expended during an eruption can be quite enormous, dangerous, and both life and property threating,  the atmospheric discharge of ash can also be a major hazard to aviation as well as the local health communities.

The recent eruption of Okmok (1st eruption - July 12) volcano in the Alaskan Aleutian Islands has garnered some recent press in the USA which started as recently as July 12, 2008 (see photo above - courtesy NOAA).  Days later (July 17th) part of the plume was seen coming into our own Pacific Northwest (CIMMS blog).  However, there have been many other important eruptions around the world which have already impacted the lives of many and continue threaten many more.  The Chaitin Volcano in Chili is a good example (see photos from National Geographic here).  Below are links to many of the volcano centers around the world, including their most recent and active volcanoes:

Anchorage Volcanic Ash Advisory Center (Okmok - Alaska, USA);  Buenos Aires VAAC (Ubinas - Peru); Darwin VAAC (Rabaul - New Britain); Tokyo VAAC (Sakurajima - Japan); Toulouse VAAC (Sete Cidades - Azores); Washington VAAC (Tungurahua - Ecuador).

Other important links which include volcanic (ash) eruption concerns:

Alaska Aviation Weather Unit; and NOAA/NWS Aviation Weather Center �