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College of DuPage Severe Weather Symposium Downers Grove, Illinois, 6 November 2009

The Un derstanding S evere T hunderstorms and A lberta B oundary L ayers E xperiment (UNSTABLE) 2008: Preliminary Results. Neil M. Taylor 1 , D. Sills 2 , J. Hanesiak 3 , J. A. Milbrandt 4 , C. D. Smith 5 , G. Strong 6 , S. Skone 7 , P. J. McCarthy 8 , and J. C. Brimelow 3

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College of DuPage Severe Weather Symposium Downers Grove, Illinois, 6 November 2009

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  1. The Understanding Severe Thunderstorms and Alberta Boundary Layers Experiment (UNSTABLE) 2008: Preliminary Results Neil M. Taylor1, D. Sills2, J. Hanesiak3, J. A. Milbrandt4, C. D. Smith5, G. Strong6, S. Skone7, P. J. McCarthy8, and J. C. Brimelow3 1Hydrometeorology and Arctic Lab, Environment Canada 2Cloud Physics and Severe Weather Research Section, Environment Canada 3Centre for Earth Observation Science (CEOS), University of Manitoba 4Recherche en Prévision Numérique [RPN] (Numerical Weather Prediction Research Section), Environment Canada 5Climate Research Division, Environment Canada 6Department of Earth and Atmospheric Sciences,University of Alberta (Adjunct) 7Department of Geomatics Engineering, University of Calgary 8Prairie and Arctic Storm Prediction Centre, Environment Canada College of DuPage Severe Weather Symposium Downers Grove, Illinois, 6 November 2009

  2. Outline • UNSTABLE Rationale • Experimental Design • Special Instrumentation and NWP • Observations from 13 July 2008: Characterization of a moisture / convergence boundary in Alberta • Summary • Project Status

  3. 27-32 Edmonton Saskatoon Calgary Regina > 32 Winnipeg Canada’s Population Density (2006) > 40 deaths and $2.5 B in property damage since 1981 22-26 UNSTABLE Rationale Existing real-time surface observations over a region of the AB foothills

  4. Transition Zone – Potential Gradient in Latent Heat Flux Mixed / Coniferous Forest Low ET Prairie Crops / Grassland High ET Rationale:Ecoclimate Regions and ET

  5. Red Deer Secondary Domain Targeting Storm Evolution 15km Spacing Primary Domain Targeting Storm Initiation 25km Spacing Calgary ExperimentalDesign UNSTABLE Goals • Improve understanding of ABL processes and CI • Improve accuracy and lead time for warnings • Assess utility of high-res NWP to resolve processes and provide guidance • Revise conceptual models for CI and severe wx 3 Main Science Areas • ABL moisture and convergence boundaries • Surface processes (heat flux) • High resolution NWP model forecasts of CI and severe weather

  6. MARS Trailer (AERI, WV Radiometer, Radiosondes, Cloud Base Temp.) WMI aircraft w/ AIMMS-20 Instrument Package (T, P, RH) CRD Mobile Radiosonde Trailer and Interior Tethersonde System Special Instrumentation AMMOS ATMOS (Automated Mobile Meteorological Observation System) (Automated Transportable Meteorological Observation System)

  7. Daily 2.5-km and Nested 1.0-km GEM LAM Runs in Real-Time 2.5 km GRID 1-km GRID Daily real-time runs Standard and experimental fields Images and data archived

  8. An Aside: What’s in a name? • Existing Alberta-specific CI and severe weather outbreak conceptual models had become outdated => little to no focus on mesoscale boundaries • Knott and Taylor (2000) first investigated role of surface moisture gradient and convergence boundary in Alberta severe storms – referred to boundary as a dryline • Later studies (e.g., Taylor 2001, 2004, Hill 2006) considered the boundary further but limited in-situ observations obtained • An objective of UNSTABLE is to characterize this boundary and associated role in CI and storm evolution • Are boundary characteristics consistent with a dryline? • What conceptual model should be used by forecasters? • What are implications for forecasting / nowcasting development, evolution, and CI? Using the current operational network? • Focus mainly on characterization of the boundary itself (not synoptic environment, storms and severe weather, etc.) • Surface Maps (θ and Td) • Fixed Mesonet Station Observations • AMMOS Observations • Soundings • Aircraft Observations

  9. + : hr - 30 to 45 min + : hr - 45 to 59 min + : hr - 15 min + : hr - 15 to 30 min 50 km 50 km 1200 UTC – 13 July 2008Potential Temperature (K) and Dewpoint (°C) Weak moisture gradient across sloping terrain

  10. + : hr - 30 to 45 min + : hr - 45 to 59 min + : hr - 15 min + : hr - 15 to 30 min 50 km 50 km 1300 UTC – 13 July 2008Potential Temperature (K) and Dewpoint (°C)

  11. + : hr - 30 to 45 min + : hr - 45 to 59 min + : hr - 15 min + : hr - 15 to 30 min 50 km 50 km 1400 UTC – 13 July 2008Potential Temperature (K) and Dewpoint (°C)

  12. + : hr - 30 to 45 min + : hr - 45 to 59 min + : hr - 15 min + : hr - 15 to 30 min Convergence in wind field Well-defined thermal gradient develops 50 km 50 km 1500 UTC – 13 July 2008Potential Temperature (K) and Dewpoint (°C) Development of Cu / Tcu

  13. + : hr - 30 to 45 min + : hr - 45 to 59 min + : hr - 15 min + : hr - 15 to 30 min Cu / Tcu 50 km 50 km 1600 UTC – 13 July 2008Potential Temperature (K) and Dewpoint (°C)

  14. + : hr - 30 to 45 min + : hr - 45 to 59 min + : hr - 15 min + : hr - 15 to 30 min 50 km 50 km 1700 UTC – 13 July 2008Potential Temperature (K) and Dewpoint (°C) Inferred Inferred Cu / Tcu

  15. + : hr - 30 to 45 min + : hr - 45 to 59 min + : hr - 15 min + : hr - 15 to 30 min CI along boundary Cu / Tcu 50 km 50 km 1800 UTC – 13 July 2008Potential Temperature (K) and Dewpoint (°C) Via aircraft observations

  16. + : hr - 30 to 45 min + : hr - 45 to 59 min + : hr - 15 min + : hr - 15 to 30 min Cu / Tcu 50 km 50 km 1900 UTC – 13 July 2008Potential Temperature (K) and Dewpoint (°C) Via aircraft observations

  17. + : hr - 30 to 45 min + : hr - 45 to 59 min + : hr - 15 min + : hr - 15 to 30 min 50 km 50 km 2000 UTC – 13 July 2008Potential Temperature (K) and Dewpoint (°C)

  18. + : hr - 30 to 45 min + : hr - 45 to 59 min + : hr - 15 min + : hr - 15 to 30 min 50 km 50 km 2100 UTC – 13 July 2008Potential Temperature (K) and Dewpoint (°C)

  19. + : hr - 30 to 45 min + : hr - 45 to 59 min + : hr - 15 min + : hr - 15 to 30 min 50 km 50 km 2200 UTC – 13 July 2008Potential Temperature (K) and Dewpoint (°C)

  20. + : hr - 30 to 45 min + : hr - 45 to 59 min + : hr - 15 min + : hr - 15 to 30 min 50 km 50 km 2300 UTC – 13 July 2008Potential Temperature (K) and Dewpoint (°C)

  21. + : hr - 30 to 45 min + : hr - 45 to 59 min + : hr - 15 min + : hr - 15 to 30 min 50 km 50 km 0000 UTC – 14 July 2008Potential Temperature (K) and Dewpoint (°C)

  22. + : hr - 30 to 45 min + : hr - 45 to 59 min + : hr - 15 min + : hr - 15 to 30 min 50 km 50 km 0100 UTC – 14 July 2008Potential Temperature (K) and Dewpoint (°C)

  23. + : hr - 30 to 45 min + : hr - 45 to 59 min + : hr - 15 min + : hr - 15 to 30 min 50 km 50 km 0200 UTC – 14 July 2008Potential Temperature (K) and Dewpoint (°C)

  24. + : hr - 30 to 45 min + : hr - 45 to 59 min + : hr - 15 min + : hr - 15 to 30 min 50 km 50 km 0300 UTC – 14 July 2008Potential Temperature (K) and Dewpoint (°C)

  25. + : hr - 30 to 45 min + : hr - 45 to 59 min + : hr - 15 min + : hr - 15 to 30 min 50 km 50 km 0400 UTC – 14 July 2008Potential Temperature (K) and Dewpoint (°C)

  26. + : hr - 30 to 45 min + : hr - 45 to 59 min + : hr - 15 min + : hr - 15 to 30 min 50 km 50 km 0500 UTC – 14 July 2008Potential Temperature (K) and Dewpoint (°C)

  27. + : hr - 30 to 45 min + : hr - 45 to 59 min + : hr - 15 min + : hr - 15 to 30 min 50 km 50 km 0600 UTC – 14 July 2008Potential Temperature (K) and Dewpoint (°C)

  28. Synoptic Network Mesonet Stations 13 July 08Instruments FCA Stations (T/RH only) Mobile Soundings (MB) Fixed Soundings Tethersonde GPS PW MB2 MM Tracks AMMOS • 2 + 1 mobile mesonets • 2x mobile radiosonde (MB2 with AERI, WVR) • 2x fixed radiosonde • Aircraft • Tethersonde • Fixed mesonet • GPS PW • Fixed profiling radiometer MB1 Aircraft Axis MM3 AB4 MM2 P4 50 km

  29. Thermal Transition Pre-Boundary Thermal Transition ~ 1850 Boundary Passage 1944-1946 Boundary Passage 1958-2000 Boundary Passage 1907-1909 ΔTd = 6.3 C Δqv = 3.0 gkg-1 Δ = 0.4 K Δv = 0.2 K ΔTd = 6.7 C Δqv = 3.2 gkg-1 Δ = 0.0 K Δv = 0.6 K ΔTd = 5.1 C Δqv = 2.5 gkg-1 Δ = 0.4 K Δv = 0.1 K AB4 (FOPEX) 1800 – 2100 UTC1-min Observations

  30. Pre-Boundary Thermal Transition 2225 Merged Boundary Passage 0254-0313 Boundary Passage 2324-2359 ΔTd = 10.0 C Δqv = 4.6 gkg-1 Δ = -0.5 K Δv = 1.3 K ΔTd = 8.7 C Δqv = 3.9 gkg-1 Δ = 2.9 K Δv = 2.2 K P4 (ATMOS) 2200 - 0330 UTC1-min Observations (86 km SSE of AB4)

  31. 2 4 1 3 6 5 CONVERGENCE CONVERGENCE P4 (ATMOS) 2319 – 0004 UTC θ (K), θv (K), qv (g kg-1), wind barbs Moisture Boundary Passage 2324 2359 θv qv θ ½ Barb = 2.5 ms-1 Full Barb = 5.0 ms-1

  32. Pre-boundary convergence with slight cooling P4 (ATMOS) 0240 – 0318 UTC θ (K), θv (K), qv (g kg-1), wind barbs Moisture Boundary Passage 0313 0254 θv θ qv ½ Barb = 2.5 ms-1 Full Barb = 5.0 ms-1

  33. 6 panel MM1 transects Temperature (K) T and Td (°C), Mixing Ratio (g kg-1) Time (UTC) 20:47:00 - 20:50:00 (N) θv 20:37:30 - 20:42:50 20:14:30 - 20:17:30 θ qv 3 2 1 21:35:54 - 21:44:30 21:16:30 - 21:21:20 20:54:30 - 20:58:50 (N) 5 4 6

  34. 2 5 4 1 3 CONVERGENCE CONVERGENCE CONVERGENCE CONVERGENCE AMMOS 20:47:00 – 20:50:00 UTCθ (K), θv (K), qv (g kg-1), wind barbs ½ Barb = 2.5 ms-1 Full Barb = 5.0 ms-1 629 m From Transect 3 ΔTd = 8.3 C Δqv = 3.7 gkg-1 Δ = 0.0 K Δv = -0.7 K

  35. Elevated Residual Layer MB1 (Blue) and MB2 (Red)Soundings Valid 00 UTC 00 UTC Td MB2 MB1 Dry ABL (MB1):~ 3700 m, warmer, westerly winds nearly throughout Moist ABL (MB2)*: ~ 1400 m, cooler, veering winds * MB2 appears to be under influence of storm outflow at this time

  36. Elevated Residual Layer MB1 (Blue) and WVX (Red)Soundings Valid 00 UTC 00 UTC Td MB1 Dry ABL (MB1):~ 3700 m, warmer, westerly winds nearly throughout Moist ABL (MB2)*: ~ 750 m, cooler, veering winds * MB2 is 68 km SE of MB1

  37. 13 July Aircraft Flight17:55:26 – 19:23:04 • 13 July flight - traverses and descending spirals at either end of the transect • Spirals to the SW just barely penetrated moist air in NE quadrant • Data gridded at 500 m (100 m) resolution in horizontal (vertical) • Recognize issues with simultaneous measurements and displacement along axis

  38. Top of Moist ABL Aircraft Obs. (17:55:26 – 19:23:04) Mixing Ratio (g/kg) Artifact of aircraft Spiral * 6 6 6 • Plot shows aircraft, sounding, and surface observations along axis • Top of moist ABL estimated from aircraft and sounding data • Dry boundary defined by strongest gradient in moisture and slopes towards the moist (and cooler) air • Suggestion of gravity waves or roll circulations above the moist ABL 7 4 5 7 6 7 AB4 AB3 7 P1 P2 Terrain exaggerated in vertical P3 ‘x’ distance (km) * Indicates along-line variability in moisture (and other) gradient(s)

  39. Aircraft Obs. (17:55:26 – 19:23:04) Potential Temperature (K) 304 303 306 • Top of moist ABL from previous figure – within θ gradient • From surface maps and aircraft observations there may be a separation between cooler, capped air downslope (NE) and thermal transition zone toward moisture boundary upslope (SW) • Convective inhibition weakened in transition zone favouring CI closer to the moisture / convergence boundary 303 305 304 302 302 301 301 303 302 301 300 300 AB4 AB3 P1 P2 Terrain exaggerated in vertical P3 ‘x’ distance (km)

  40. Aircraft Obs. (17:55:26 – 19:23:04) Virtual Potential Temperature (K) 305 307 304 • Strongest horizontal θv gradient across moisture boundary • θv gradient also across thermal transition zone • Data infer a horizontal density gradient from the warm, dry air (less dense) to the cool, moist air (more dense) 304 303 306 303 305 302 302 304 303 302 AB4 301 AB3 P1 P2 Terrain exaggerated in vertical P3 ‘x’ distance (km)

  41. Corresponding Aircraft Observation Domain Pot. Temp. 1.0 km GEM LAM Ascent Descent 310 308 306 304 302 300 298 T+7 hr forecast valid 2200 UTC along same axis used for aircraft analysis

  42. Ziegler and Rasmussen (1998) Conceptualization Elevated Residual Layer overrunning capped ABL Warm, dry air mixed to the surface. Gravity waves or remnant role circulations(?) Thermal transition zone between moisture boundary to the SW and cooler, capped ABL to the NE (CIN reduced towards moisture boundary) 1-1.5 km Cool, moist and capped ABL Component of flow upslope Terrain exaggerated in vertical

  43. Summary • Moisture / convergence line associated with CI resolved more completely in Alberta than ever before • Establish boundary continuity over 100 km (SFC obs + SATPIX) • Higher θ, θv (lower density) on dry side of the boundary within a deep ABL • Lower θ, θv (higher density) on moist side of the boundary within a shallower ABL • Changes in mixing ratio (dewpoint) as high as 5 g kg-1(13 °C) over distances on order of 100 m • Boundary gradients as high as 18 g kg-1 km-1 and 42 °C km-1 (one instance of 2 g/kg over only 46 m = 42 g kg-1 km-1 !?) • Horizontal θ gradient (~ 5 K) between the main moisture boundary and cool, capped region to the east (~ 30km wide) favouring CI closer to the boundary (CIN decreases to the W, SW) • Additional change in θ and θv across the moisture boundary itself (θv gradient up to 2.8 K km-1 from AMMOS data) • Observed characteristics consistent with dryline conceptual model • Detailed thermodynamic and kinematic structure resolved via mobile surface obs. within overall moisture gradient (more analysis req’d)

  44. UNSTABLE Status • Analysis ongoing with plans for two papers in the short term • BAMS article providing overview of the project and variety of preliminary results • A more detailed look at 13 July focussing on dryline characteristics • Still many questions to be answered including • Relative importance of moist / dry air processes for dryline genesis/evolution? • Formal association of observed dryline to CI and storms? • How use conceptual model + operational observation networks to ID, monitor, and nowcast dryline evolution and CI in operational setting? • Preparations to begin soon for full-scale project tentatively scheduled for summer 2012 • Mobile radar (!) including refractivity data • Flux measurements (surface and airborne) • Additional instrumented aircraft • More mesonet stations / soundings • Longer observation period • Changes to domain, station placement (?)

  45. Acknowledgements / References • UNSTABLE 2008 was mainly funded from within Environment Canada with in-kind support from Canadian Universities (U of Manitoba, U of Alberta, U of Calgary) Acknowledgements • Dr. Shawn Marshall, University of Calgary – Foothills Climate Array (FCA) surface observations • Dr. Gerhard Reuter, University of Alberta – contributions to aircraft and mobile surface observations • Blaine Lowry for production of surface maps References • Hill, L. M., 2006: Drylines observed in Alberta during A-GAME. M.Sc. Thesis, Department of Earth and Atmospheric Sciences, University of Alberta, 111pp. • Knott, S. R. J. and N. M. Taylor, 2000: Operational Aspects of the Alberta severe weather outbreak of 29 July 1993. Nat. Wea. Digest, 24, 11-23. • Taylor, N. M., 2001: Genesis and Morphology of the Alberta Dryline. Presented at the 35th Annual CMOS Congress, Winnipeg, Manitoba. • Taylor, N. M., 2004: The dryline as a mechanism for severe thunderstorm initiation on the Canadian Prairies. Presented at the 38th Annual CMOS Congress, Edmonton, Alberta. • Ziegler, C. L. and E. N. Rasmussen, 1998: The initiation of moist convection at the dryline: Forecasting issues from a case study perspective. Wea. Forecasting, 13, 1106–1131.

  46. Thank You! Photo courtesy Dave Sills

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