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Jackson State Univ.: "A preliminary investigation of the initiation of deep summertime convection in weakly sheared environments using the Mobile, AL WSR-88D"

Final Report


The project met its objectives based on data collected during the summer of 1996: stratification of base state flow with respect to the observed location of convective initiation; determination of the kinematic and thermodynamic characteristics (and their evolution with time) associated with the large scale base state flow and local atmosphere prior to convective initiation; and determination of causative factors within the Mobile forecast zones based on assimilation of radar and other datasets and analyses.

These objectives were met only through extensive work by the NWS PI and coordination with the UNIV PI. As the focus of the project was operational, much of the work was completed on site. Although work was shared between PIs, the characterization and statistical assessment of base state flow regimes was focused on by the UNIV PI whereas the extensive analysis of thermodynamic characteristics was focused on by the NWS PI. Both shared in the determination of causative factors and provided each other with "food for thought" by offering counter-arguments to proposed mechanisms for convective initiation. This was particularly important in the development of an operational conceptual model that was presented to the NWS MOB staff. Two NWS MOB forecasters assisted in data collection and analysis, as did a student from Northeast Louisiana University and a student from JSU. An additional outcome of this project has been the examination of convective activity during the summer 1997 season by the NWS PI.

The research provided a means by which summertime convective initiation under weak shear could be better redirected based on available observational tools, guidance, and meteorological "know-how". It provided an improvement over a simple "sea-breeze forecasting approach" by giving greater insight into the process of boundary layer growth and change which results in different patterns of convective distribution from day to day in spite of the outward appearance of the similarity of one day to the next.

In particular, it was found that close examination of the lower atmosphere's characteristics on any day provides valuable information that can readily improve a forecast. For example, the application of isentropic analysis, virtually unheard of for a tropical/summer season environment, can greatly enhance the reliability of a convective forecast and improve a forecaster's POP forecast. The application of isentropes appears to improve the prediction of areal coverage of convective activity. Another significant outcome is the use of mean sounding information and a modified 1800 UTC sounding to determine the most unstable parcel's level. This work confirmed suspicions that it is the surface parcel that is most unstable and that can be lifted freely or by terrain-induced circulations. It also forced the PIs to consider the entire process of boundary layer development and convective growth.

All of these were critical in the development of a conceptual operational model and forecasting approach for use at the NWS MOB. An interesting feature was the "Tale of Two Counties" in which initiation focused on one side of Mobile Bay under a southeast flow regime and on the other (as a mirror image) when the flow was southwest. In addition, there appeared favorable convergence zones or axes and sea-breeze penetration varied according to which portion of the forecast area was considered. The fact that this research chose not to focus on the sea breeze specifically was crucial in "seeing" these features. It also more readily allowed a forecast that was not sea breeze dependent.

It should also be noted that although high-resolution satellite imagery was helpful, it was not essential in determining initiation. This was due to the greater timeliness of radar data and the fact that satellite imagery was often unavailable or incomplete. Radar data was also critical in determining surface boundaries based on both reflectivity and velocity information. Satellite information appeared to be most useful when diagnosing the potential temperature gradient expected between land and sea (or land and bay).


The primary exchange (due to distance) was the presentation of a training seminar in April 1997. The seminar provided forecasters (and a JSU student) a view of the nature of weak shear convection in the context of locale, synoptics, and climatology. It then went on to illustrate project results while also simulating a timed operational environment in which groups of forecasters had to decide where initiation would occur and why. This gave a clear indication of lessons learned and forecaster bias when faced with a "typical summertime pattern" in which a chance of thunderstorms is forecast.

Two NWS MOB forecasters, Don Faulkner and Brian Ohara, routinely participated in this research project by providing analysis, additional interpretation. A JSU student assisted in development of figures for the initial submittal of a manuscript to Weather and Forecasting. The UNIV PI expects to make use of project results in a spring seminar class on convection.


After completion of the project an article was submitted to Weather and Forecasting on May 28, 1997. Since that time reviewer comments have been received and the paper has been given provisional acceptance:

Medlin, J. M., and P. J. Croft, 1997. A preliminary investigation and diagnosis of weak shear summertime convective initiation for extreme southwest Alabama. Submitted to Weather and Forecasting, in revision.

A training seminar (as previously listed) was also conducted:

"A Preliminary Investigation of Summertime Convective Initiation using the NWSO Mobile, AL WSR-88D in Weak Vertical Wind Shear Environments" by Paul J. Croft and Jeffrey M. Medlin. Training seminar conducted at the NWS MOB, Mobile, AL, 14 April 1997.

A listing of project related presentations accepted are as follows:

Croft, P. J., and J. M. Medlin, 1997. "Coastal Convective Initiation in Summer as a Function of Seasonal Progression and Physiography" accepted for oral presentation at the National Weather Association Annual Meeting, 19-24 October 1997; and at the Second Conference on Coastal Atmospheric and Oceanic Prediction and Processes, American Meteorological Society, 11-16 January 1998

Watts, M., and P. J. Croft, 1997. "Studying Convective Initiation: A Student's Perspective" accepted for oral presentation at the NWA Annual Meeting and for poster presentation at the AMS Educational Symposium.

Croft, P. J., and J. M. Medlin, 1996. "Diagnosis of Summer Convective Initiation Under Weak Shear" accepted for poster presentation at the NWA Annual Meeting, 1-6 December 1996.


4.1 University Perspective

The COMET partnership provided for in this grant was critical to JSU in that it allowed direct collaboration with the NWS that led to direct impact on students in the Meteorology Program in addition to operational forecasting. In particular, the ability to work with professional meteorologists was paramount to success as there were no graduate students to involve in the research. This coupled with the use of the latest technology for observation, analysis, and prediction at the NWS (and unavailable in the UNIV setting) made the grant a "win-win" situation.

As with any proposal or project, some problems exist or were encountered. The relatively small amount of funding dollars associated with such grants are difficult for a PI to justify to the home institution for approval. The limited budgets also tend to limit involvement of more students and the travel associated with research and presentation. On the University side, difficulties were encountered internally when establishing the grant account and when billing was made. In several instances these difficulties were quite time-consuming and in two cases nearly resulted in plans being changed during the project. One example was the provision of hiring (and giving support) to a student over the summer. The university was unable to act quickly and nearly lost the opportunity to support the summer student.

Although distance was a factor in the completion of this project it should not preclude similar efforts in the future, particularly if two or more NWS offices are involved. Rather, additional dollars should be made available to defray travel costs of the UNIV PI and to provide support for academic release.

The project would not have been possible, nor successful, without the support of NWS MOB MIC (Randall McKee) or the UNIV Chair of the Department of Physics, Atmospheric Sciences, and General Science. Support for this project was also provided through the Mississippi Science Partnership office at JSU (Gloria Marshall). Thanks also go to Jonathan Brazzell for his summer participation in this project. The UNIV PI offers personal thanks to the NWS PI for offering accommodations without hesitation.

4.2 NWS Perspective

Specifically, it must be mentioned, that without this project, there would have been no time platform (or monetary support) to study such an important forecast problem which affects this particular forecast zone. The results from this study have given the local forecasters at NWSO MOB a unique perspective and in-depth look at an alternative, more sophisticated, approach to a daily forecast problem whose daily strategical approach would have otherwise gone unchanged. As a NWS representative, I wholly endorse the continuation of such research program endeavors by COMET. Ultimately, the benefit is to the US taxpayer without a doubt.

One minor negative aspect... We hired a student to assist us with our data collection and research. There was a major problem with money arriving on time to pay this student. We almost lost the student due to his not receiving the money on time. In the future, the COMET Program needs to ensure that the Universities who are involved with the project, can cut the 'red tape' and respond with monetary support in a faster manner, once the project has been approved. In our case we almost lost a student due to bad timing of the arrival of the funds for the support that the student was providing.