An Examination of how Manitoba Lake Breezes may Influence. Convective Storms

Transcription

1 An Examination of how Manitoba Lake Breezes may Influence Convective Storms by Scott Kehler A report submitted to the Department of Environment and Geography, University of Manitoba, In partial fulfillment of the requirements for course ENVR 3500 April 17, 2015

2 Abstract Lake breeze data from the Effects of Lake Breezes on Weather in Manitoba (ELBOW-MB) field project were analyzed to examine the effects of lake breezes on convective storm indices. Lidar, rawinsonde, and High Resolution Deterministic Prediction System (HRDPS) data were used to compute the Lifted Condensation Level (LCL), helicity, wind shear, and vertical velocities. Observationally, LCL heights were found to decrease by between 90 and 710 m following the passage of lake-breeze fronts. In the HRDPS simulations, LCL heights increased, except in one case where a decrease was noted. It was found that helicity and wind shear changes were dependent on the orientation of the shoreline. The lake-breeze depth recorded by a Doppler lidar was greater than that simulated by the HRDPS and lidar-observed maximum vertical velocities were also larger in magnitude than in the HRDPS simulations. This study provides some initial results regarding how lake breezes may affect convective storms. Further cases will need to be amassed to generalize these results. i

3 Table of Contents Abstract... i List of Tables... iii Table of Figures... iv 1. Introduction and Background Lake Breeze Background Severe Weather Ingredients Numerical Weather Prediction Objectives Methods Stability calculations Helicity and Wind Shear Vertical Velocity Results Thermodynamics Helicity and Wind Shear Vertical Velocity Conclusion References ii

4 List of Tables Table 1: LCL heights observed by rawinsondes and simulated by the HRDPS... 9 Table 2: Rawinsonde-observed and HRDPS-simulated helicity and wind shear values. Changes in helicity and wind shear following the passage of a lake-breeze front are given in the before-after rows iii

5 Table of Figures Figure 1: ELBOW-MB Domain Map... 2 Figure 2: Rawinsonde (HRDPS) profiles showing the environment before (solid) and after (dashed) the passage of a lake-breeze front. Green lines are dewpoint and red lines are temperature Figure 3: Rawinsonde-observed hodographs. Figures on the left represent the terrestrial environment and the figures on the right represent the marine environment. Red numbers indicate the height of the observation in kilometres Figure 4: HRDPS-simulated hodographs. Figures on the left represent the terrestrial environment and the figures on the right represent the marine environment. Red numbers indicate the height of the observation in kilometres Figure 5: Lidar-observed winds in the u, v, and w components. U and v winds are shown as wind barbs (in knots) and the w-component of the wind is shown using the colourfilled contours. The black line seperates regions of positive and negative u- componentwinds as a method of approximating the boundary between the terrestial and marine air masses Figure 6: HRDPS-simulated wind in in u, v, and w components. U and v winds are shown as wind barbs (in knots) and the w-component of the wind is shown using the colour-filled contours. The black line seperates regions of positive and negative u- component winds as a method of approximating the boundary between the terrestial and marine air masses iv

6 1. Introduction and Background 1.1 Lake Breeze Background Lake breezes can influence the development and evolution of thunderstorms. Studies in southern Ontario have also shown that lake breezes can influence tornado frequency (King et al., 2003). A case study from Australia concluded that a sea breeze was likely important in the development of a tornado (Sills et al., 2004). In southern Manitoba, tornadoes have been known to occur near Lakes Winnipeg and Manitoba (e.g. Hobson, 2011). However, there is an absence of research that explores the link, if any, between lake breezes and severe convective storms in Manitoba. Lake breezes are a diurnal, mesoscale 1 phenomenon. They develop due to differential heating between a lake and its adjacent land during the daytime. Since water has a higher specific heat capacity than soil, the land heats faster than the lake. This causes the air over the land to expand more rapidly than over the lake, generating relative low pressure over the land and relative high pressure over the lake. As a result of these pressure perturbations, a pressure gradient develops between the lake and adjacent land surfaces, causing a lake-to-land flow near the surface and a land-to-lake flow aloft (return flow). The basic physical reasons for why lake breezes occur are well understood, however the impacts of lake breezes are less understood and the focus of most research. For a more thorough introduction regarding lake-breeze dynamics, the reader should consult Sills (1998) and Curry et al. (2015a). 1 Orlanski (1975) defines mesoscale as being 2 to 2000 km 1

7 Lake breezes were a largely unexplored topic in Manitoba until recently. In 2013, the Effects of Lake Breezes on Weather in Manitoba field project (ELBOW-MB) undertook the first in-depth field study of lake breezes in Manitoba. The domain of the ELBOW- MB field study is shown in Figure 1. Kehler (2014) provided some initial modeling results from ELBOW-MB. Future papers (soon to be submitted: Curry et al. (2015b) and Kehler et al. (2015)) will provide general observational and modeling results from ELBOW-MB; however neither paper specifically focuses on the influence of lake breezes on severe weather. Figure 1: ELBOW-MB Domain Map 1.2 Severe Weather Ingredients Canada ranks second in the world for tornado occurrences, with approximately 70 reported every year (Sills et al., 2012). Within Canada, southern Manitoba is one of the most tornado prone regions in Canada, with greater than 2 tornadoes per km² yr ¹ 2

8 (Sills et al., 2012). In addition, southern Manitoba is the location of Canada s strongest recorded tornado, the F5 tornado that occurred in Elie, MB in 2007 (Hobson, 2011). Severe convective storms require several ingredients to develop. These ingredients are commonly described as moisture, instability, wind shear, and a triggering mechanism. Moisture refers to the presence of high levels of water vapour in the boundary layer. Instability refers to the situation in which a lifted parcel becomes warmer than the environmental temperature at its Level of Free Convection (LFC) and then proceeds to accelerate upward. Wind shear is the presence of increasing wind speeds and/or changing wind directions with height in the troposphere. Lastly, a triggering mechanism is some phenomenon (e.g. a lake breeze) that helps lift an air parcel to its LFC. 1.3 Numerical Weather Prediction It has been shown that Numerical Weather Prediction (NWP) models can simulate lake breezes. Sills et al. (2011) showed GEM-LAM simulations of Ontario lake breezes and Kehler (2014) showed HRDPS simulations of Manitoba lake breezes. This paper uses the same HRDPS as Kehler (2014) to provide simulations of atmospheric stability, wind shear/helicity, and lift. The HRDPS used by Kehler (2014) had a grid spacing of 2.5 km on a 250 x 400 grid centred on the ELBOW-MB Domain (see Figure 1). For full details about the HRDPS used in this paper the reader is encouraged to consult Kehler et al. (2015) and Mailhot et al. (2014). 1.4 Objectives Lake-breeze research in Canada has been fairly extensive, as discussed previously in this section. However, little research has been done to explore the effects of lake breezes 3

9 on severe weather indices in Manitoba, despite the connection between lake breezes and convective storms. This paper will examine the influence of lake breezes on convective storms with respect to the following objectives: 1) How does atmospheric stability differ on the marine and terrestrial sides of lakebreeze fronts? 2) What magnitude of change in helicity and bulk shear can be expected as a result of a lake-breeze front passage? 3) What magnitude of vertical velocities can occur along a lake-breeze front? 4

10 2. Methods This paper will use two cases from the ELBOW-MB field project to fulfil the objectives stated in section 1.4; these cases are July 13 and 17, These cases were chosen because sufficient data were collected to perform the analyses of interest to this paper. Both cases have been previously identified and discussed using the Sills et al. (2011) criteria in Kehler et al. (2015). However, previous analyses of these cases did not examine the influence of those lake breezes on convective storm indices. Note that no convective storms were present in either of these cases, so the analyses in this paper suggest what might have occurred, hypothetically, had thunderstorms been present. 2.1 Stability calculations To examine objective 1 of this paper, atmospheric stability for the two aforementioned lake-breeze cases was analyzed. Atmospheric stability is typically quantified using CAPE; however no CAPE was observed by rawinsondes in these cases. Therefore, the lifted condensation level (LCL) was calculated and used as a proxy for CAPE. If the LCL height increased, it was assumed that CAPE would decrease. Conversely, if the LCL height decreased it was assumed that CAPE would increase. This is not necessarily an accurate assumption, since it is possible that CAPE would not change even if the LCL height changes. However, since there is no CAPE in these cases, this is the only alternative to assess stability as it relates to the potential for deep moist convection. The LCL height was calculated using three different parcel methods: surface-based, mixed-layer, and most-unstable parcels. The surface-based method lifted a parcel using 5

11 the surface temperature and dewpoint values. The mixed-layer method took the lowest 100 mb mean temperature and dewpoint to get a representative mixed boundary-layer parcel. Lastly, the most-unstable method computed the LCL height from most unstable parcel in the lowest 300 mb of the troposphere. All three measures are provided to indicate the sensitivity of the parcel selection to the calculation of LCL height. 2.2 Helicity and Wind Shear Low-level wind shear is a very important factor in the development of tornadoes. Craven & Brooks (2004) found that significant tornadoes are commonly associated with large 0-1 km wind shear and low mixed-layer LCL heights. The 0-1 km wind shear vector is a simply the vector difference in wind between the surface and 1 km AGL. Helicity is also an important factor in the prediction of tornadoes, quantified in this paper as storm-relative helicity (SRH; Davies-Jones et al., 1990). SRH is dependent on both the environmental winds and the storm motion. However, the storm motion cannot be measured by rawinsondes; therefore the Bunkers et al. (2000) and Maddox (1976) methods are used to predict storm motions. These two storm motion methods are used to show the sensitivity of SRH to the storm motion vector. Three variants of SRH were calculated for the analysis: 0-1, 0-2, and 0-3 km. 2.3 Vertical Velocity Lake breezes are known to enhance and/or initiate thunderstorms (King et al., 2003; Sills et al., 2004; Sills et al., 2011). However, little research has been done in Canada to examine the vertical velocity structure across lake-breeze fronts. Sills et al. (2011) and Kehler (2014) use vertical velocity data plotted in 2-D (x-y directions) to determine the location of lake-breeze fronts, but these analyses do not include a vertical 6

12 dimension. In this paper vertical velocities are also explored in 2-D, however emphasis is on the x-z dimension (cross-section) to explore the vertical structure of lake-breeze fronts. Doppler lidar data from ELBOW-MB is used as an observational source of vertical velocities. The HRDPS is then compared to the lidar data to provide a modelling perspective on vertical structure. Characteristics of the vertical structure are quantified, including the magnitude and location of maximum vertical velocities as well as the height of the marine air mass. 7

13 3. Results 3.1 Thermodynamics Rawinsonde observations from ELBOW-MB and HRDPS simulations were used to study changes in atmospheric stability that resulted from lake-breeze front passages on July 13 and 17, Figure 2 shows profiles that were observed and simulated for these cases (HRDPS and Rawinsonde profiles show the same location in each case). Two profiles are shown on each graph, an initial profile, showing the terrestrial air mass, and a final profile, showing the marine air mass (following the passage of a lake-breeze front). The July 13 initial profile is from 2300 UTC and the final profile is from 0100 UTC (on July 14). The July 17 initial profile is from 2300 UTC and the final profile is from 2200 UTC. The final profile is from a later time than the initial profile in the July 17 case because the marine environment was sampled first. For the purposes of consistency, we assume that the initial profile represents the terrestrial environment and the final profile represents the marine environment. The rawinsonde observations in Figure 2 show an increase in moisture (dewpoint values) following the passage of lake-breeze fronts. In the July 13 case there is a modest increase in temperature, but in the July 17 case there is a decrease in temperature. Since the rawinsondes were not launched at the same time, the temperature increase on July 13 may represent a modification of the marine air mass from solar heating. Kehler et al. (2015) showed that the lake-breeze circulations observed during ELBOW-MB tended to have small temperature differences between the marine and terrestrial environments. However, increases in dewpoint toward the marine environment tended to be more 8

14 Figure 2: Rawinsonde (HRDPS) profiles showing the environment before (solid) and after (dashed) the passage of a lake-breeze front. Green lines are dewpoint and red lines are temperature. Table 1: LCL heights observed by rawinsondes and simulated by the HRDPS Rawinsonde LCL (m) HRDPS LCL (m) Date SBLCL MLLCL MULCL SBLCL MLLCL MULCL July 13 23Z July 14 01Z Difference July 17 22Z July 17 23Z Difference

15 significant in magnitude than temperature decreases. Using these profiles the LCL heights could be calculated using the methods discussed in section 2.1. Table 1 shows the computed values. The data shown in Table 1 indicates that the rawinsonde-observed LCL heights decreased in both cases across all measures. However, surprisingly the LCL heights increased in all but one measure for HRDPS-simulated lake breezes. This is surprising since the passage of a lake-breeze front should result in additional boundary-layer moisture, causing the LCL height to drop. The reason that the HRDPS did not accurately simulate these changes in the July 17 case is due to the fact that the lake-breeze front in the model did not propagate onshore, preventing the marine air mass from reaching the comparison point. It is unknown why the model did not correctly simulate the LCL height changes in the July 13 case. 3.2 Helicity and Wind Shear One of the defining characteristics of a lake-breeze front is a wind shift, making the front a convergent region (Lyons, 1972). The orientation of the shoreline will, in part, also determine the orientation of the lake-breeze front and therefore the convergent zone. In this section changes in wind speed and direction are analyzed in the vicinity of lakebreeze fronts. Figure 3 shows rawinsonde-observed hodographs before and after the passage of lake-breeze fronts. Figure 4 shows HRDPS-simulated hodographs at the same locations and times as those that were observed by rawinsondes. The hodographs shown in Figures 3 and 4 provide a visualization of the changes in helicity that occur along lakebreeze fronts. In general, the hodographs tended to retain their shape following the passage of lake-breeze fronts. However, the size of the hodographs tended to be altered. 10

16 Table 2 quantifies these changes using SRH. In the July 13 case the observed helicity decreased in all measures following the passage of the lake-breeze front. The location of the rawinsonde launch of July 13 was the southern shore of Lake Manitoba. Given the location of the rawinsonde launch, one would expect to see a southerly component wind shift to a northerly component onshore wind as the lake-breeze front passed. This was in fact the case as a south-westerly surface wind shifted to a north-easterly surface wind. This caused the helicity to decline under both the bunkers and traditional storm motion methods, with the highest decline being in the 0-2 and 0-3 km Bunkers SRH at -71 m² s ². The HRDPS simulations also showed a decline in helicity across all calculations, with the Bunkers 0-1 km SRH seeing the largest decline at -44 m² s ². Declines in helicity were larger using the bunkers method compared to the traditional method. Bunkers declines ranged from -71 to -74 m² s ² while traditional-method declines ranged from -15 to -42 m² s ². The rawinsondes for the July 17 case were launched from the western shoreline of Lake Winnipeg. Therefore, one would expect to see a westerly-component wind shift to an easterly-component wind following the passage of a lake-breeze front. That was in fact the case, as shown by the hodographs in Figure 3. Since the low-level winds back under the aforementioned conditions, larger helicity values would be expected. This was the case, as shown in Table 2, with helicity increasing across all rawinsonde-observed measures. The largest helicity increase was in 0-3 km SRH using the bunkers method, which increased by 109 m² s ². This increase is quite substantial and could mean the difference between a non-supercell, supercell, or tornadic environment 11

17 Table 2: Rawinsonde-observed and HRDPS-simulated helicity and wind shear values. Changes in helicity and wind shear following the passage of a lake-breeze front are given in the before-after rows. Rawinsonde Traditional/Helicity Bunkers/Helicity Wind Shear Date 0-1km 0-2km 0-3km 0-1km 0-2km 0-3km 0-1km July 13 23Z July 14 01Z Before-After July 17 22Z July 17 23Z Before-After HRDPS Traditional/Helicity Bunkers/Helicity Wind Shear Date 0-1km 0-2km 0-3km 0-1km 0-2km 0-3km 0-1km July 13 23Z July 14 01Z Before-After July 17 22Z July 17 23Z Before-After

18 Figure 3: Rawinsonde-observed hodographs. Figures on the left represent the terrestrial environment and the figures on the right represent the marine environment. Red numbers indicate the height of the observation in kilometres. 13

19 Figure 4: HRDPS-simulated hodographs. Figures on the left represent the terrestrial environment and the figures on the right represent the marine environment. Red numbers indicate the height of the observation in kilometres. 14

20 (Rasmussen & Blanchard, 1998). The smallest increase in helicity was 43 m² s ² in 0-2 km SRH using the traditional method. Unlike the rawinsonde observed helicity values, the HRDPS-simulated SRH values for July 17 both increased and decreased depending on the measure. Changes in SRH ranged from -46 m² s ² using the 0-2 km bunkers method to a 15 m² s ² increase using the 0-3 km traditional method. The hodographs simulated by the HRDPS for July 17 (Figure 4) are backing in nature, which is opposite of what was actually observed. As noted in the thermodynamics section, the HRDPS did not propagate the lake-breeze front onshore in the July 17 case, maintaining the terrestrial air mass at the comparison point. This is one of the main reasons why the HRDPS did not correctly simulate the changes in helicity on July km wind shear changes mirrored the helicity changes to some extent. During the July 13 case, no change in 0-1 km wind shear was observed by rawinsondes as the lakebreeze front passed through. However, the HRDPS showed a -4 m s ¹ decrease in 0-1 km wind shear due to the passage of the lake-breeze front. During the July 17 case, the rawinsonde-observed 0-1 km wind shear increased by 10 m s ¹, but the HRDPSsimulated 0-1 km wind shear declined by 1 m s ¹. The large increase in 0-1 km wind shear observed by the rawinsonde on July 17 could certainly have an impact on a convective storm in the region. The incorrect simulation of the 0-1 km wind shear by the HRDPS can be mainly attributed to the model s inability to propagate the lake breeze onshore, as discussed previously. 15

21 3.3 Vertical Velocity The July 17 lake breeze case is analyzed in this section to better understand the vertical structure of the lake-breeze front. The July 13 case was excluded because no lidar data was available. Figure 5 shows lidar-observed wind speeds in all three directions (u, v, and w). Figure 6 shows HRDPS-simulated winds in the same three directions. Figure 5 shows the maximum vertical velocities observed by the lidar were located between 400 and 500 m above ground level (AGL) at the leading edge of the lake-breeze front (around profile 160). The maximum vertical velocity was 5.3 m s ¹, located at 500 m AGL. Behind the leading edge of the lake-breeze front is a subsident region, perhaps indicative of the relative high pressure located over the lake. 16

22 Figure 5: Lidar-observed winds in the u, v, and w components. U and v winds are shown as wind barbs (in knots) and the w- component of the wind is shown using the colour-filled contours. The black line seperates regions of positive and negative u- componentwinds as a method of approximating the boundary between the terrestial and marine air masses 17

23 Figure 6: HRDPS-simulated wind in in u, v, and w components. U and v winds are shown as wind barbs (in knots) and the w- component of the wind is shown using the colour-filled contours. The black line seperates regions of positive and negative u- component winds as a method of approximating the boundary between the terrestial and marine air masses. 18

24 Figure 6 shows a cross-section of the July 17 lake-breeze front in the HRDPS. A maximum in vertical velocities is noted near 900 mb, with the maximum vertical velocity being between -2.0 and -2.5 Pa s ¹. These HRDPS-simulated vertical velocities are roughly an order of magnitude smaller than those observed by the lidar, since 1 m s ¹ is approximately equal to 10 Pa s ¹ below the 700 mb level. Lyons & Olsson (1973) reported upward velocities in excess of 1 m s ¹ along the Chicago lake-breeze front, providing additional evidence to support the HRDPS-simulated upward velocities being an order of magnitude too small. The 900 mb level is approximately 800 m AGL, meaning that the maximum vertical velocity in the model was approximately 300 m higher than observed by lidar. Changes in the height of maximum vertical velocities will alter the ability of a lake-breeze front to lift parcels to their level of free convection (LFC). However, the ability of a lake-breeze front to initiate convection will vary depending on the synoptic and mesoscale conditions of the day (e.g. the degree of convective inhibition and height of the LFC). The maximum height of the top of the lidar-observed lake-breeze shown in Figure 5 is approximately 850 m. The maximum height of the top of the HRDPS-simulated lake breeze in Figure 6 is approximately 300 m. Interestingly, the lidar-observed lake breeze is deeper than the one simulated by the HRDPS, but the location of the maximum vertical velocities is higher in the HRDPS. It is unknown why these differences exist between the HRDPS and lidar data. This study does not have sufficient data to provide an explanation for these differences. 19

25 4. Conclusion This paper analyzed the stability, helicity, wind shear, and vertical velocity changes associated with the passage of lake-breeze fronts. Conclusions related to the objectives in section 1.4 are stated below: 1) It was determined that atmospheric stability tends to decrease following the passage of lake-breeze fronts. LCL heights fell in all rawinsonde-observed cases; with decreases ranging from 90 to 710 m. However, the HRDPS did not recreate these decreases. In fact, most HRDPS simulations had higher LCL heights after the passage of lake-breeze fronts. These errors in the HRDPS are partly the result of errors in lake breeze propagation. The lack of cases in this paper does not allow these results to be generalized for all lake-breezes, although it seems probable that most lake breezes will have lower LCL heights in their marine air mass given that moisture is known to increase in the marine environment. 2) Helicity changes along lake-breeze fronts were found to be dependent on the orientation of the shoreline. The July 13 case along the southern shoreline of Lake Manitoba showed helicity decreases, while the July 17 case had helicity increases toward the marine environment. In the July 17 case 0-3 km helicity increased by 109 m² s ² following the passage of the lake-breeze front. Conversely, 0-3 km helicity decreased by 71 m² s ² following the passage of the lake-breeze front on July 13. Both of these helicity values were calculated using the Bunkers storm motion and represent significant changes that would affect the potential of a given storm to develop a mesocyclone. Wind shear mirrored the helicity changes to 20

26 some extent, with the 0-1 km wind shear increasing by 10 m s ¹ in the July 17 case, but not changing at all in the July 13 case. HRDPS simulations of 0-1 km wind shear showed a decrease in both cases of -4 m s ¹ and -1 m s ¹, respectively. 3) Lidar data were used to quantify vertical velocities observationally for the July 17 case and the HRDPS provided a modelling comparison. It was found that the lidar-observed vertical velocities were an order of magnitude larger than the HRDPS-simulated vertical velocities. This large difference in vertical velocities magnitudes would likely affect the HRDPS s ability to accurately initiate convection, although no evidence was presented to support that claim. It was also found that the location of the maximum vertical velocities was approximately 300 m higher in the HRDPS compared to lidar observations. This difference in the location of the vertical velocity maximums may also affect the HRDPS s ability to initiate convection. In the future, additional lake breeze cases should be amassed to try and generalize these results to all Manitoba lake breezes. This study merely provides a starting point from which to begin analyzing lake-breeze structure as it relates to convective storm indices. 21

27 5. References Bunkers, M. J., Kilmowski, B. A., Zeitler, J. W., Thompson, R. L., & Weisman, M. L. (2000). Predicting Supercell Motion Using a New Hodograph Technique. Wea. Forecasting, 15, Craven, J. P., & Brooks, H. E. (2004). Baseline Climatology of Sounding Derived Parameters Associated with Deep, Moist Convection. Nat. Wea. Digest, 28, Curry, M., Hanesiak, J., & Sills, D. (2015a). A radar-based investigation of lake breezes in southern Manitoba, Canada. Atmosphere-Ocean, in press, doi: / Curry, M., Hanesiak, J., Kehler, S., Sills, D., & Taylor, N. (2015b). Ground-based observations of the thermodynamic and dynamic properties of lake-breezes in southern Manitoba, Canada. To be submitted to: Boundary Layer Meteorology. Davies-Jones, R. P., Burgess, D. W., & Foster, M. (1990). Test of helicity as a tornado forecast parameter. 16th Conf. on Severe Local Storm (pp ). Kananaskis Park, AB, Canada: Amer. Meteor. Soc. Hobson, J. (2011). Meteorological Analysis of the 22 June 2007 F5 Tornado in Elie, Manitoba, Masters Thesis, University of Manitoba, 132 pp. [Available from the Department of Environment and Geography, University of Manitoba, 220 Sinnott Bldg. Fort Gary Campus, Winnipeg, Manitoba, Canada, R3T 2N2]. 22

28 Kehler, S. (2014). GEM-LAM Simulations of Manitoba Lake Breezes, Honours Thesis, University of Manitoba, 56 pp. [Available from the Department of Environment and Geography, University of Manitoba, 220 Sinnott Bldg. Fort Gary Campus, Winnipeg, Manitoba, Canada, R3T 2N2]. Kehler, S., Hanesiak, J., Curry, M., Sills, D., & Taylor, N. (2015). HRDPS simulations of Manitoba lake breezes. Will be submitted to: Atmosphere-Ocean. King, P. W., Leduc, M. J., Sills, D. M., Donaldson, N. R., Hudak, D. R., Joe, P., & Murphy, B. P. (2003). Lake Breezes in Southern Ontario and Their Relation to Tornado Climatology. Meteorological Service of Canada, Lackmann, G. (2011). Midlatitude Synoptic Meteorology. Boston: American Meteorological Society. Lyons, W. A. (1972). The climatology and prediction of the Chicago lake breeze. J. Appl. Meteor, 11, Lyons, W. A., & Olsson, L. E. (1973). Detailed mesometeorological studies of air pollution dispersion in the Chicago lake breeze. Mon. Wea. Rev., 101, Maddox, R. A. (1976). An evaluation of tornado proximity wind and stability data. Mon. Wea. Rev., 104, Mailhot, J., Milbrandt, J. A., Giguère, A., McTaggart-Cowan, R., Erfani, A., Denis, B.,... Vallée, M. (2014). An Experimental High-Resolution Forecast System During the Vancouver 2010 Olympic and Paralympic Games. Pure Appl. Geophys., 171, doi: /s

29 Orlanski, I. (1975). A rational subdivision of scales for atmospheric processes. Bull. Amer. Meteor. Soc., 56, Rasmussen, E. N., & Blanchard, D. O. (1998). A baseline climatology of soundingderived supercell and tornado forecast parameters. Wea. Forecasting, 13, Sills, D. (1998). Lake and Land Breezes in Southwestern Ontario: Observations, Analyses and Numerical Modeling Sills, D. M., Brook, J. R., Levy, I., Makar, P. A., Zhang, J., & Taylor, P. A. (2011). Lake breezes in the southern Great Lakes region and their influence during BAQS-Met Atmospheric Chemistry and Physics, 11(15), Sills, D. M., Wilson, J. W., Joe, P. I., Burgess, D. W., Webb, R. M., & Fox, N. I. (2004). The 3 November tornadic event during Sydney 2000: Storm evolution and the role of low-level boundaries. Weather and Forecasting, 19, Sills, D., Cheng, V., McCarthy, P., Rousseau, B., Waller, J., Elliott, L.,... Auld, H. (2012). Using tornado, lightning and population data to identify tornado prone areas in Canada. 26th Conf. on Severe Local Storms, (pp. 1-10). Nashville, TN. Retrieved from 24