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Purdue University: "Wet versus dry periods in the Midwest during the winters of 1997-98 El Nino and 1998-99 La Nina"

Final Report

Project Objectives and Accomplishments

The overall goal of our project was to investigate the impact of the 1997-98 El Niño on synoptic-scale temperature, and especially precipitation, distributions over the Midwestern United States. Prior to the start of this project, we had determined that the Midwest was a pivotal region of highly variable weather during an El Niño event and, therefore, a difficult area for which to forecast, particularly in the wintertime. Our study focused on the month of January 1998 that was near the peak of the 1997-98 El Niño. Normally, the Midwest is warm and dry during an El Niño; however, in January 1998 the region was wetter than usual, with approximately twice as much precipitation as the average wintertime El Niño amount. Our preliminary examination of daily weather at a midwestern station (Lafayette, IN) revealed that most of the precipitation occurred from 3-8 January and that the rest of the month was dry. Thus, the objectives of our research project were to diagnose the large-scale circulation patterns for each of these periods. More specifically, we proposed three objectives that are paraphrased below.

  1. Acquire January 1998 temperature and precipitation data for several stations across the Midwest to see if the weather at Lafayette was representative of midwestern conditions.

  2. Acquire upper air data from NCEP to examine the circulation patterns during the wet (dry) period of 3-8 (9-3 1) January 1998.

  3. Separate the precipitation that occurred from 3-8 January into rain versus snow cases.

The research team that has been working to achieve these objectives during the past year is given below, together with each member's responsibilities. Julie Adolphson was the NWS co-PI and was responsible for using GEMPAK on the SOO/SAC Workstation to produce most of our climatological and daily weather maps from NCEP data. She also provided considerable insight into the interpretation of our results. Sam Lashley, lead forecaster, processed all of the midwestern station data of temperature and precipitation. In the end, we selected 10 stations as being representative. Sam also presented one of our jointly published preprint papers at a national conference in January 2000 (see publication list in section 3). Greg Lamberty, NWS hydrologist, provided river gauge data and gave us advice on our wet versus dry periods. We also benefited from the advice and technical assistance provided by forecasters, Brian O'Hara, a specialist in winter weather, and Tim Reaugh, who has experience in climatology. The participants at Purdue, in addition to Dr. Dayton Vincent, co-PI, were Jason Giovannettone, a graduate student, and Angela Lese, an undergraduate Honors student. Both are conducting research that will lead to theses next year. Furthermore, Angela is working at the NWS Office in North Webster, IN (where we conduct our joint research) as an intern this summer.

Our accomplishments to-date are now summarized. Figure I shows that the average precipitation computed for the 10 stations, which we use to represent the Midwest, was 150% of normal during January 1998.The average snowfall (not shown) was considerably less than normal due to the extremely warm conditions that existed across the region. The figure also shows that 9 of the 10 stations had above normal precipitation. During an El Niño, the Midwest can expect to have about 70% of normal precipitation, thus the region received approximately twice as much precipitation as expected. A typical example of the temperature and precipitation records across the Midwest is shown in Fig. 2 for Peoria, IL. It shows that nearly all of the precipitation that fell during the month occurred from 3-8 January. We also examined the January 1998 hydrological records from the gauges of nine rivers across Indiana and found that all of them peaked between 6-12 January. In order to examine this period further, we partitioned the upper air geopotential height and wind data into two periods, 3-8 January, when the Midwest was wet, and 9-31 January, when the region was dry. The results are shown in Fig. 3. The most salient feature is the difference in the jet stream patterns between 3-8 and 9-31 January. In particular, note that, relative to the jet core during the 3-8 January period, the Midwest is in a highly favorable location for upper level horizontal divergence (i.e., in the right rear quadrant of the jet axis with the trough (ridge) of cyclonic (anticyclonic) flow 90' to its left (right)) (Bluestein 1993). This divergence pattern would support low-level convergence, mid-level upward motion, and precipitation. To further emphasize this feature, height and wind anomalies, calculated by subtracting the January 1998 means from each of the two period means, are shown in Fig. 4. It is seen that high (low) height anomalies are located over the Midwest during 3-8 (9-3 1) January.

Summary of University/NWS Exchanges

Thus far, our research has led to two jointly-published papers, the contents of which have been presented at national scientific meetings of the American Meteorological Society. One paper was given at the 8th Conference on Climate Variations, held at Denver, CO in September 1999, and the other was presented at the 15th Conference on Hydrology at Long Beach, CA in January 2000. Copies of these papers are included with this report. In addition, our joint research group has submitted an Abstract of a paper we hope to present at the 10th Symposium on Education at Albuquerque, NM in January 2001. A copy of this document is also part of this report.

As mentioned earlier, one of the Purdue participants, Angela Lese, was selected to be a meteorological intern and is working this summer at the NWS Office in North Webster, IN with Julie Adolphson and other forecasters. Finally, it's worth noting that Julie was selected in December 1999 to be on a NWS team that is responsible for developing an implementation plan (or "roadmap") for NWS climate services. In addition, she participated in the initiation and writing of a Professional Development Series (PDS) document for climate in the spring of 2000. Both of these groups have interests that are similar to our joint research.

Presentations and Publications

Vincent, D.G., A. Lese and J. Adolphson, 1999: Climate/weather relationships over the Midwest during El Niño 1997-98. Preprint, 8th Conference on Climate Variations, Denver, CO, September 1999, 4 pp.

Vincent, D.G., J. Adolphson, S. Lashley, J. Giovannettone and A. Lese, 2000: The distribution of wintertime precipitation over the Midwest during 1997-98 El Niño and 1998-99 La Niña. Preprint, 15th Conference on Hydrology, Long Beach, CA, 10-14 January 2000, 4 pp.

Adolphson, J., D.G. Vincent, A. Lese, S. Lashley, J. Giovannettone, B. O'Hara, T. Reaugh, G. Lamberty and S. O'Connor, 2001: Enhancing public awareness of climate through a COMET outreach project. Abstract submitted for presentation at the 10th Symposium on Education, Albuquerque, NM, 14-19 January 2001.

Summary of Benefits and Problems Encountered
Completed by academic partner

Dr. Vincent's group at Purdue has benefited from the partner's project in the following ways. First, they have become familiar with some of the procedures used by operational forecasters. This is especially true for the two students who are working on the project because they have spent time at the NWS Office in North Webster. In particular, one of the students, Angela Lese, has been an intern at that office during the summer. Second, some of the research conducted by both students has been accomplished at the NWS office. Their research will result in an M.S. thesis by Jason Giovannettone and a B.S. thesis by Angela Lese. Both of these accomplishments are a benefit not only to the students, but to Purdue, as well. Finally, some of the results of our research have been used by Dr. Vincent in courses he teaches at Purdue. Relatively few problems have arisen to this point. When they occurred, they were overcome and did not impede on the progress being made by the students.

Completed by NWS

Many aspects of our joint work have been relevant to the operational activities of the NWS. First, the research has helped the participating forecasters enhance their educational background, since Dr. Vincent is a specialist in tropical-extratropical interactions that includes the impact of El Niño and La Niña events on North American weather patterns. Second, we envision that our results will promote better use of NWS-prepared forecasts to the general public and specific user communities, since a better understanding of the impact of El Niño and La Niña processes on the weather in the Midwest is our goal. Finally, our research should provide beneficial feedback to the Climate Prediction Center (CPQ at NOAA concerning their monthly and seasonal forecasts, especially in the Midwest region.

Figure 1

Figure 2