1. An Historical Analysis of Transient Rain Bearing Systems in the NAME Domain: The Impact of Inverted Troughs on Monsoon Rainfall Art Douglas and Phil Englehart Creighton University

2. Research Objectives 1. To develop an historical climatology of transient synoptic systems in northern Mexico. 1. To develop an historical climatology of transient synoptic systems in northern Mexico. 2. To determine relationships between these transient systems and fluctuations in summer rainfall. 2. To determine relationships between these transient systems and fluctuations in summer rainfall. 3. To relate variability in the frequency of transient systems to large scale oceanic and atmospheric anomalies. 3. To relate variability in the frequency of transient systems to large scale oceanic and atmospheric anomalies. 4. To provide a benchmark for modeling studies in order to determine model performance relative to the prediction of these transient features and their associated rainfall. 4. To provide a benchmark for modeling studies in order to determine model performance relative to the prediction of these transient features and their associated rainfall.

3. Transient Synoptic Features Affecting Northern Mexico 1. Tropical Cyclones (Published). 1. Tropical Cyclones (Published). 2. Inverted Troughs: Cold and Warm. 2. Inverted Troughs: Cold and Warm. 3. Cold Fronts. 3. Cold Fronts. 4. Cutoff Lows. 4. Cutoff Lows. 5. Open Troughs. 5. Open Troughs.

8. Transient Synoptic Features Affecting Northern Mexico 1. Tropical Cyclones (Published). 1. Tropical Cyclones (Published). 2. Inverted Troughs: Cold and Warm. 2. Inverted Troughs: Cold and Warm. 3. Cold Fronts. 3. Cold Fronts. 4. Cutoff Lows. 4. Cutoff Lows. 5. Open Troughs. 5. Open Troughs.

10. NOAA NWS LIBRARY

12. Meridional Wind Time Section 8 July to 12 August 2005

13. Meridional Wind Time Section July 1973

16. Average Daily Rainfall (mm) Inverted Trough Days vs. Days with No Synoptic Feature Increase in Daily Rainfall (%) Inverted Trough Days with respect to Days with No Synoptic Feature

17. Inverted Troughs Contribution to Seasonal (June-Sept) Rainfall (1967-2001) Average Rainfall (mm) Percent Contribution to Seasonal Total

18. RAINFALL Associated with INVERTED TROUGHS as a function of TROUGH POSITION (i.e. Displacement East (-) or West (+) of the Division Location in º Long.) SONORA/SINALOA DURANGO TAMAULIPAS/NUEVO LEON

19. CONTRIBUTION OF INVERTED TROUGHS TO SEASONAL TOTAL RAINFALL 2004/CLIMO

21. Transient Synoptic Features Affecting Northern Mexico 1. Tropical Cyclones (Published). 1. Tropical Cyclones (Published). 2. Inverted Troughs: Cold and Warm. 2. Inverted Troughs: Cold and Warm. 3. Cold Fronts. 3. Cold Fronts. 4. Cutoff Lows. 4. Cutoff Lows. 5. Open Troughs. 5. Open Troughs.

23. VIS 16Z October 7, 2005

24. Total Rainfall October 2-7, 2005

26. TAMAULIPAS/NUEVO LEON (DIVISION 7) Percentage of Total Seasonal Rainfall Associated with Fronts (< 350 km)

30. Summary and Conclusions 1. A 35 year climatology of transient synoptic features indicates that NAME 2004 was characterized by: a. Cold Front Days 200% of normal. b. Inverted Trough Days 70% of normal. c. Cutoff Low Days 90% of normal. d. Open Trough Days 170% of normal. 2. Inverted troughs provide 20%-25% of the summer rainfall received in NC and NE Mexico.

31. 3. Rainfall with IV troughs peaks when the system is overhead in NC Mexico. Rainfall peaks in Western Mexico when the IV system is 3° to 4° upstream: associated with MCS development ahead of IV troughs (downslope, weak capping). 4. IV Rainfall in NE Mexico peaks when the system is 4° upstream and this may be related to disruption of the normal divergent trade system in the western Gulf of Mexico 5. In NE Mexico cold fronts provide about 6% of the normal summer rainfall (June to September).