The Understanding Severe Thunderstorms and Alberta Boundary Layers Experiment (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 1 Hydrometeorology and Arctic Lab, Environment Canada 2 Cloud Physics and Severe Weather Research Section, Environment Canada 3 Centre for Earth Observation Science (CEOS), University of Manitoba 4 Recherche en Prévision Numérique [RPN] (Numerical Weather Prediction Research Section), Environment Canada 5 Climate Research Division, Environment Canada 6 Department of Earth and Atmospheric Sciences, University of Alberta (Adjunct) 7 Department of Geomatics Engineering, University of Calgary 8 Prairie and Arctic Storm Prediction Centre, Environment Canada College of DuPage Severe Weather Symposium Downers Grove, Illinois, 6 November 2009

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

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

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

Calgary Red Deer Experimental Design 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 1. ABL moisture and convergence boundaries 2. Surface processes (heat flux) 3. High resolution NWP model forecasts of CI and severe weather Secondary Domain Targeting Storm Evolution Primary Domain Targeting Storm Initiation 15km Spacing 25km Spacing

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

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

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 T d ) –Fixed Mesonet Station Observations –AMMOS Observations –Soundings –Aircraft Observations

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

AB4 (FOPEX) 1800 – 2100 UTC 1-min Observations Pre-Boundary Thermal Transition ~ 1850 Thermal Transition Boundary Passage Boundary Passage Boundary Passage ΔT d = 5.1  C Δq v = 2.5 gkg -1 Δ  = 0.4 K Δ  v = 0.1 K ΔT d = 6.3  C Δq v = 3.0 gkg -1 Δ  = 0.4 K Δ  v = 0.2 K ΔT d = 6.7  C Δq v = 3.2 gkg -1 Δ  = 0.0 K Δ  v = 0.6 K

P4 (ATMOS) UTC 1-min Observations (86 km SSE of AB4) Pre-Boundary Thermal Transition 2225 Boundary Passage Merged Boundary Passage ΔT d = 10.0  C Δq v = 4.6 gkg -1 Δ  = -0.5 K Δ  v = 1.3 K ΔT d = 8.7  C Δq v = 3.9 gkg -1 Δ  = 2.9 K Δ  v = 2.2 K

P4 (ATMOS) 2319 – 0004 UTC θ (K), θ v (K), q v (g kg -1 ), wind barbs Moisture Boundary Passage qvqv θvθv θ ½ Barb = 2.5 ms -1 Full Barb = 5.0 ms CONVERGENCE

P4 (ATMOS) 0240 – 0318 UTC θ (K), θ v (K), q v (g kg -1 ), wind barbs Moisture Boundary Passage qvqv θvθv θ Pre-boundary convergence with slight cooling ½ Barb = 2.5 ms -1 Full Barb = 5.0 ms -1

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

AMMOS 20:47:00 – 20:50:00 UTC θ (K), θ v (K), q v (g kg -1 ), wind barbs 629 m CONVERGENCE ½ Barb = 2.5 ms -1 Full Barb = 5.0 ms -1 From Transect 3 ΔT d = 8.3  C Δq v = 3.7 gkg -1 Δ  = 0.0 K Δ  v = -0.7 K

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

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

13 July Aircraft Flight 17:55:26 – 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

Aircraft Obs. (17:55:26 – 19:23:04) Mixing Ratio (g/kg) 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 Terrain exaggerated in vertical AB4 AB3 P1 P2 P3 Artifact of aircraft Spiral * * Indicates along-line variability in moisture (and other) gradient(s) ‘x’ distance (km) Top of Moist ABL

Aircraft Obs. (17:55:26 – 19:23:04) Potential Temperature (K) 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 Terrain exaggerated in vertical AB4 AB3 P1 P2 P3 ‘x’ distance (km)

Aircraft Obs. (17:55:26 – 19:23:04) Virtual Potential Temperature (K) AB4 AB3 P1 P2 P3 Terrain exaggerated in vertical Strongest horizontal θ v gradient across moisture boundary θ v 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) ‘x’ distance (km)

1.0 km GEM LAM Pot. Temp. Ascent Descent T+7 hr forecast valid 2200 UTC along same axis used for aircraft analysis Corresponding Aircraft Observation Domain

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

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, θ v (lower density) on dry side of the boundary within a deep ABL –Lower θ, θ v (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 θ v across the moisture boundary itself (θ v 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)

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 (?)

Acknowledgements / References 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 Nat. Wea. Digest, 24, 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– 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)

Thank You! Photo courtesy Dave Sills