The Impact of the Saint Lawrence Valley on Warm Season Precipitation Distribution, 1979-2008

1. The Impact of the Saint Lawrence Valley on Warm Season Precipitation Distribution, 1979-2008 Giselle C. Dookhie, John R. Gyakum, and Eyad H. Atallah Department of Atmospheric and Oceanic Sciences McGill University Montreal, QB NROW XII

2. Purpose • To identify synoptic-scale flow associated with extreme precipitation • To examine mesoscale modulations by existing orography NROW XII

3. Motivation Precipitation map from Hurricane Ike (2008). Precipitation appears more dependent on Valley location than actual cyclone track

4. Quantification of expected precipitation inspired by: -Fred Sanders • P : Precipitation Rate • g : gravity • ω: vertical ascent • (drs/dp)ma: Saturation mixing ratio along a moist adiabat • p:pressure NROW XII

5. Data • Environment Canada hourly surface observations and 24hrly accumulated precipitation amounts at Montreal/Pierre Elliott Trudeau International Airport, Quebec (YUL) for the period 1979-2008 • National Centers for Environmental Prediction (NCEP) North American Regional Reanalysis (NARR) and Global Reanalysis • National Oceanic and Atmospheric Administration (NOAA) National Hurricane Center (NHC) Best Track Data NROW XII

6. Methodology: Created a heavy precipitation dataset 24hourly accumulated precipitation Calculated 90th Percentile Legend: Data-red Process- Green Result- yellow Threshold: 20mm NROW XII

7. Criteria for an event: Legend: Data-red Process- Green Result- yellow Step 1: 20mm in 1day or 20mm in 2 consecutive days Step 2: CHECK: Are consecutive days related? Select the date with the heaviest 24hrly accumulated precipitation Hourly surface Obs.

8. NROW XII

9. Seasonality • 221 precipitation events (blue) • Highest frequency of precipitation eventsin August, with the highest frequency of hurricane events in September • 11/12yrs that a tropical storm has an influence on a heavy precipitation event; hurricanes ranked within the top 2 events of each year NROW XII

10. 221 Events Ranked heavy precipitation events within each year from largest-smallest Selected heaviest precipitation event for each year Selected all cases of tropical storm influences over 30yr period regardless of intensity 45 Events NROW XII

11. Composite Anomaly and Mean 500hPa Geopotential Height Source: the NOAA-ESRL Physical Sciences Division, Boulder Colorado from their Web site at http://www.esrl.noaa.gov/psd/ NROW XII

12. Methodology: zonal flow Category: Example of partitioning technique and compositing NROW XII

13. Partitioning 45 cases based on 500mb flow pattern • Below are sample individual cases of the heaviest precipitation day within the zonal flow category • Within the zonal flow category, the heaviest precipitation day of each individual case are averaged over a 24hour period Those averages are used to create a composite plot, for example: Zonal Flow category containing 8 individual cases … … NROW XII

14. 500hPa Height and Vorticity Zonal flow (n=8): Amplified flow(n=13): 500hPa composite heights (m; contoured) and absolute vorticity (10-5 s-1; shaded) averaged over the event day with the heaviest precipitation NROW XII

15. MSLP and 1000-500hPa thickness Zonal flow cases (8 individual cases): MSLP (solid) and 1000-500hPa thickness (dotted) Amplified flow cases (13 individual cases): MSLP (solid) and 1000-500hPa thickness (dotted) NROW XII

16. 250hPa Wind Maxima Variability Zonal flow (n=8): Amplified flow (n=13): 250hPa Wind maxima (kts; contoured) representative of individual cases within each category NROW XII

17. Zonal Flow Category Amplified Flow Category NROW XII

18. Precipitable water: Weighted climatology subtracted from composite precipitable water for each case Zonal flow Category Amplified flow Category • Where: • PWTR = precipitable water (kgm-2) • w(p) = mixing ratio at pressure p • Averaged over 1000hPa-300hPa NROW XII

19. Frontogenesis (10-1K 100km-13h-1): 975-900hPa Total frontogenesis Ageostrophic component Geostrophic component Zonal Flow Category Amplified Flow Category NROW XII

20. Mesoscale: Possible Impacts of the saint Lawrence valley NROW XII

21. NROW XII

22. Conclusions • Structural differences: • Baroclinicity • Moisture supply O(1) from Gulf of Mexico and Atlantic, for Zonal flow and Amplified flow category respectively • Mesoscale Influences: • Frontogenesis along the axis of the Saint Lawrence Valley • Wind channeling (Northeasterly-Southwesterly) NROW XII

23. Continued Research • For each group: • Composite analysis: Moisture and Instability • Case studies NROW XII

24. References • Atallah, Eyad H. and John R. Gyakum. The Impact of the Saint Lawrence Valley on the Precipitation Distributions of Hurricanes Katrina and Rita. Nov. 2009. PowerPoint. • Carrera, M. L., J. R. Gyakum, and C. A. Lin, 2009: Observational study of wind channeling within the St. Lawrence River Valley. Journal of Applied Meteorology and Climatology, 48, 2341-2361. • Durnford, D. A., 2001-Thesis: An Analysis of Montreal’s Record-Breaking Heavy Rainfall Event of 8-9 November 1996, and a Comparison with its Best Analogue. • Environment Canada Climate Data Online (http://www.climate.weatheroffice.gc.ca/climateData/canada_e.html) • Fischer, A. P., 1998 –Thesis: A Synoptic Climatology of Montreal Precipitation. • Kalnay, E., and Coauthors, 1996: The NCEP/NCAR 40-Year Reanalysis Project. Bull. Amer. Meteor. Soc., 77, 437–471. • Koch, S. E., M. DesJardins, and P. J. Kocin, 1983: An interactive Barnes objective map analysis scheme for use with satellite and conventional data. J. Climate Appl. Meteor., 22, 1487–1503. • Milrad, Shawn. “Re: EPI equation?” E-mail to Giselle Dookhie. 28 Oct. 2010. • National Hurricane Center (NHC) best-track archive dataset (http://www.nhc.noaa.gov) NROW XII

25. Additional Slide(s) NROW XII

26. Alberta-Clipper Type Category (n=4) 500mb Trough West of Montreal Category (n=7) 500mbTrough over Montreal Category (n=13) NROW XII