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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.

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Presentation on theme: "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."— Presentation transcript:

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 11/5/2010NROW XII

2 Purpose 1.To identify synoptic-scale flow associated with extreme precipitation 2.To examine mesoscale modulations by existing orography 11/5/2010NROW XII

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

4 11/5/2010NROW XII -Fred Sanders P : Precipitation Rate g : gravity ω: vertical ascent (dr s /dp) ma : Saturation mixing ratio along a moist adiabat p:pressure Quantification of expected precipitation inspired by:

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 11/5/2010NROW XII

6 Methodology: Created a heavy precipitation dataset 11/5/2010NROW XII Calculated 90 th Percentile Threshold: 20mm 24hourly accumulated precipitation Legend: Data-red Process- Green Result- yellow

7 11/5/2010 Criteria for an event: Hourly surface Obs. Select the date with the heaviest 24hrly accumulated precipitation CHECK: Are consecutive days related? 20mm in 1day or 20mm in 2 consecutive days Legend: Data-red Process- Green Result- yellow Step 1: Step 2:

8 11/5/2010NROW XII

9 Seasonality 221 precipitation events (blue) Highest frequency of precipitation events in 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 11/5/2010NROW XII

10 11/5/2010NROW XII Selected all cases of tropical storm influences over 30yr period regardless of intensity Selected heaviest precipitation event for each year Ranked heavy precipitation events within each year from largest-smallest 221 Events 45 Events

11 Composite Anomaly and Mean 500hPa Geopotential Height 11/5/2010NROW XII Source: the NOAA-ESRL Physical Sciences Division, Boulder Colorado from their Web site at http://www.esrl.noaa.gov/psd/

12 ZONAL FLOW CATEGORY: EXAMPLE OF PARTITIONING TECHNIQUE AND COMPOSITING Methodology: 11/5/2010NROW XII

13 11/5/2010 NROW XII … … Partitioning 45 cases based on 500mb flow pattern Below are sample individual cases of the heaviest precipitation day within the zonal flow category Those averages are used to create a composite plot, for example: Zonal Flow category containing 8 individual cases Within the zonal flow category, the heaviest precipitation day of each individual case are averaged over a 24hour period

14 Zonal flow (n=8): Amplified flow(n=13): 11/5/2010NROW XII 500hPa composite heights (m; contoured) and absolute vorticity (10 -5 s -1 ; shaded) averaged over the event day with the heaviest precipitation 500hPa Height and Vorticity

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) 11/5/2010NROW XII

16 250hPa Wind maxima (kts; contoured) representative of individual cases within each category 250hPa Wind Maxima Variability Zonal flow (n=8):Amplified flow (n=13): 11/5/2010NROW XII

17 11/5/2010NROW XII Amplified Flow Category Zonal Flow Category

18 Precipitable water: Weighted climatology subtracted from composite precipitable water for each case 11/5/2010NROW XII Where: PWTR = precipitable water (kgm -2 ) w(p) = mixing ratio at pressure p Averaged over 1000hPa-300hPa Amplified flow CategoryZonal flow Category

19 Total frontogenesis Frontogenesis (10 -1 K 100km -1 3h -1 ): 975-900hPa Ageostrophic componentGeostrophic component 11/5/2010 NROW XII Zonal Flow Category Amplified Flow Category

20 Mesoscale: Possible Impacts of the saint Lawrence valley 11/5/2010NROW XII

21 11/5/2010NROW 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) 11/5/2010NROW XII

23 Continued Research For each group: Composite analysis: Moisture and Instability Case studies 11/5/2010NROW 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)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)http://www.nhc.noaa.gov 11/5/2010NROW XII

25 ADDITIONAL SLIDE(S) 11/5/2010NROW XII

26 11/5/2010NROW XII Alberta-Clipper Type Category (n=4) 500mb Trough West of Montreal Category (n=7) 500mbTrough over Montreal Category (n=13)

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