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Saint Cloud State University: "A study of precipitation characteristics associated with inverted troughs"

Final Report

1.1 Introduction

The purpose of this project was to use a case study approach to analyze winter storms involving inverted troughs which had a major impact on the Northern Plains. Specifically, two cases with precipitation primarily ahead of the trough were to be compared with two cases with precipitation behind the trough (ahead and behind cases are defined in Weisman, R. A., K. G. McGregor, and P. N. Schumacher, 1998: Precipitation regimes during cold-season inverted trough cases in the Central U.S. Preprints 16th Conf. on Wea. Anal. and Forecasting, 374-376.)

The analysis of the cases were to be performed using GEMPAK at the NWS Grand Forks by Philip N. Schumacher, Science and Operations Officer, Gregory S. Frosig, NWS Forecaster, and a senior Saint Cloud State University (SCSU) meteorology student. Robert A. Weisman, the co-PI and SCSU faculty, was responsible for identifying a promising student and training this person on the background of the inverted trough problem. Jason L. Selzler was the student identified to work on this project. He spent the academic year of 1997-98 reading the previous research on inverted troughs and analyzing the composite of inverted troughs with precipitation behind under a previous grant to SCSU by the National Science Foundation. Jason then spent the summer of 1998 at NWS Grand Forks performing the analysis of the case studies on GEMPAK. All three project participants met occasionally during the period of the COMET grant to lend insight to the analysis of the cases. All participants also presented their work on inverted troughs during a workshop held in Sioux Falls in November 1998.

1.2 Description of research/development accomplishments.

A copy of the report on the case analyses is attached. Parallel results between the case studies and the composite work being pursued at SCSU indicate that the ahead cases tend to have the following characteristics:

The behind cases seem to have the following characteristics in common:

In general, the behind cases have much in common with those studied by Keshishian et al. (MWR, 1994), the only previously published work on cyclones with inverted troughs in the central U.S., while the ahead cases have very little in common with the Keshishian et al. cases.


Schumacher made two trips to SCSU during the period of the grant. He gave one seminar on a non-grant subject, The Red River Valley Floods of Spring 1997, which produced widespread interest in the entire Earth Sciences Department at SCSU.

Schumacher, Selzler, and Weisman comprised the entire body of presenters at the one-day Workshop on Forecasting Inverted Troughs in the Northern Plains, sponsored by the Sioux Falls NWS Office on November 18, 1998. Results from both the COMET grant-sponsored work and the related work supported by the SCSU NSF grant were presented to an audience of private forecasters, NWS forecasters, students, and faculty.

A regular conversation between Schumacher and Weisman on topics of local forecasting interest has continued, including information exchanges relating to the NSF sponsored research, identification of other case studies of interest to both parties and availability of data sets for analysis, and a larger project proposal involving regional NWS offices and SCSU.


Schumacher, P. N., G. S. Frosig, and R. A. Weisman, 1998: A case study of an inverted trough with precipitation located ahead. Preprints
16th Conf. Wea. Anal. and Forecasting, Amer. Meteor. Soc., Phoenix, AZ, 377.

Selzler, J. L., 1998: Invert this! A composite of inverted troughs with precipitation behind the trough. Senior research project, Saint Cloud State University.

Selzler, J. L., 1998: A composite of inverted troughs with precipitation behind the trough. Undergraduate Research Symposium. Saint Cloud State University College of Science and Engineering, April 1998.

Schumacher, P. N., J. L. Selzler, and R. A. Weisman, 1998: Workshop on precipitation organization associated with inverted troughs. National Weather Service Forecast Office, Sioux Falls, South Dakota, 18 November 1998.

Schumacher, P. N., G. F. Frosig, J. L. Selzler, and R. A. Weisman, 1999: A comparative case study of precipitation distribution associated with inverted troughs in the Central United States. 8th Conf. on Mesoscale Processes, Amer. Meteor. Soc., Boulder, CO (accepted).

Weisman, R. A., D. R. Novak, J. L. Selzler, B. C. Thomas, and P. N. Schumacher, 1999: Composite study of winter inverted trough storms in the central U.S. 8th Conf. on Mesoscale Processes, Amer. Meteor. Soc., Boulder, CO (accepted).

4.1 University's perspective

This project advanced the work on inverted troughs, which is of tremendous interest to regional operational forecasters. The workshop appears to have been successful in getting the latest information on forecast applications to those interested. Again, refer to attached comments by attendees. Word of mouth has traveled to other forecasting businesses in the area, who wish to find out about these results. Weisman will be taking advantage of his sabbatical during the 1998-99 academic year to bring the results of both the composite studies and the case studies to more of the operational forecast community. The results will also be used in future class exercises.

The ability to pay students to work on research projects has numerous benefits to the students. It allows them to work in the field to pay their bills, rather than getting a job out of the field to support themselves.The extra research experience on this and other grants has improved their placement in graduate programs (and has resulted in some students being given early assignments on research projects due to their rare research experience as undergraduates). It provided transition employment for Jason Selzler during the time that he was searching for employment after graduation and provided role-modeling for the next class, several of whom have indicated an interest in working on research projects.

The investigation begun under this COMET grant will continue beyond the end of the funding period. Work is continuing at both NWSFO Sioux Falls and SCSU on improving the understanding of inverted trough cyclones. The forecast rules developed through this project and the parallel NSF grant will applied to future cases. Refinement of these ideas will continue based upon both successful and unsuccessful application of these concepts to the operational forecast problem of the inverted trough. This work will continue well beyond the length of the grant.

The final benefit is that the work sponsored by both the COMET grant and the NSF funding has established SCSU as the only university in the region that is studying phenomena of great operational interest to regional forecasters. Regional NWS office and SCSU intend to look into other operational problems as future projects, with the goal of improving the skill of forecasting during these unique phenomena.

The only problem encountered occurred due to Jason Selzler's status as a graduate after the spring quarter of 1998. SCSU rules required that Jason be hired as a consultant since he was finished with his formal education at SCSU. This caused some confusion which was explained by correspondence between SCSU's Sponsored Programs Office and COMET.

4.2 NWS perspective

This research provided much needed guidance in forecasting precipitation associated with inverted troughs. This forecast problem is considered one of the most difficult cold-season problems by Northern Plains forecasters. However, since the mid-November workshop, there have been a couple of inverted trough cases across South Dakota. The first was a major winter storm on New Year's Day 1999. The primary storm track would have indicated little or no snow over South Dakota, but the presence of the inverted trough made it a serious forecasting problem for the state. The lead forecaster at NWS Sioux Falls noted the presence of the inverted trough. He used some of the ideas presented at the workshop to surmise that precipitation would be the heaviest along the inverted trough where there was to be ample convergence. His statements and forecasts indicated this and provided better guidance to the public on the timing of the snow. There was a second inverted trough case in mid-January 1999. Severe forecasters looked at the warm advection pattern associated with the trough and determined that precipitation would develop primarily ahead of the trough. Again, they were able to provide better timing in the public forecast on the ending of the precipitation.

Finally, our winter weather exercise in December 1998 involved a case with an inverted trough. All of the forecasters went through the exercise. In most cases, the forecasters looked for the location of the warm advection, the presence of frontogenesis (or lack thereof), and air flow in the vicinity of the trough. Most of the forecasters were able to use the knowledge gained from the workshop to determine that the snowfall would be ahead of the trough. When they noted that the trough had become stationary, many increased the precipitation amounts along and ahead of the inverted trough while not making changes behind the trough.

Overall, the results of this work have been shown to be immediately applicable to the operational forecaster. When inverted troughs are noted in the forecast models, forecasters are examining low-level warm advection and frontogenesis in order to determine the location of the precipitation.