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 Canada2Cloud Physics and Severe Weather Research Section, Environment Canada3Centre for Earth Observation Science (CEOS), University of Manitoba4Recherche en Prévision Numérique [RPN] (Numerical Weather Prediction Research Section), Environment Canada5Climate Research Division, Environment Canada6Department of Earth and Atmospheric Sciences, University of Alberta (Adjunct)7Department of Geomatics Engineering, University of Calgary8Prairie and Arctic Storm Prediction Centre, Environment Canada

College of DuPage Severe Weather SymposiumDowners 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

> 32

27-32

22-26

UNSTABLE Rationale

Canada’s Population Density (2006)

Existing real-time surface observations over a region of the AB foothills

Edmonton

CalgarySaskatoon

ReginaWinnipeg

> 40 deaths and $2.5 B in property damage since 1981

Rationale:Ecoclimate Regions and ET

Prairie Crops / GrasslandHigh ET

Mixed / Coniferous ForestLow ET

Transition Zone – Potential Gradient in Latent Heat Flux

Calgary

Red Deer

ExperimentalDesignUNSTABLE 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 Areas1. ABL moisture and

convergence boundaries2. Surface processes (heat flux)3. High resolution NWP model

forecasts of CI and severe weather

Secondary DomainTargeting Storm Evolution

Primary DomainTargeting Storm Initiation

15km Spacing

25km Spacing

AMMOS ATMOS

TethersondeSystem

CRD Mobile Radiosonde Trailer and Interior

MARS Trailer (AERI, WV Radiometer, Radiosondes, Cloud Base Temp.)

Sp

ecia

l In

stru

men

tati

on

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 Td)– Fixed Mesonet Station Observations– AMMOS Observations– Soundings– Aircraft Observations

1200 UTC – 13 July 2008Potential 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 50 km

1300 UTC – 13 July 2008Potential 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 50 km

1400 UTC – 13 July 2008Potential 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 50 km

1500 UTC – 13 July 2008Potential Temperature (K) and Dewpoint (°C)

+ : hr - 15 min+ : hr - 15 to 30 min

+ : hr - 30 to 45 min+ : hr - 45 to 59 min

Well-definedthermal gradient develops

50 km 50 km

Development

of Cu / Tcu

Convergence in wind field

1600 UTC – 13 July 2008Potential 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 50 km

1700 UTC – 13 July 2008Potential 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

Inferred

50 km 50 km

1800 UTC – 13 July 2008Potential 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 50 km

1900 UTC – 13 July 2008Potential 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 50 km

2000 UTC – 13 July 2008Potential 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 50 km

2100 UTC – 13 July 2008Potential 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 50 km

2200 UTC – 13 July 2008Potential 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 50 km

2300 UTC – 13 July 2008Potential 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 50 km

0000 UTC – 14 July 2008Potential 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 50 km

0100 UTC – 14 July 2008Potential 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 50 km

0200 UTC – 14 July 2008Potential 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 50 km

0300 UTC – 14 July 2008Potential 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 50 km

0400 UTC – 14 July 2008Potential 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 50 km

0500 UTC – 14 July 2008Potential 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 50 km

0600 UTC – 14 July 2008Potential 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 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 08Instruments

Mobile Soundings (MB)

Aircraft Axis

Synoptic NetworkMesonet StationsFCA Stations (T/RH only)

Fixed SoundingsTethersonde

GPS PW

MM TracksMB1

MB2

AMMOS

MM2

MM3AB4

P4

50 km

AB4 (FOPEX) 1800 – 2100 UTC1-min Observations

Pre-Boundary Thermal Transition ~ 1850

Thermal Transition

Boundary Passage 1907-1909

Boundary Passage 1944-1946

BoundaryPassage 1958-2000

ΔTd = 5.1 CΔqv = 2.5 gkg-1

Δ = 0.4 KΔv = 0.1 K

ΔTd = 6.3 CΔqv = 3.0 gkg-1

Δ = 0.4 KΔv = 0.2 K

ΔTd = 6.7 CΔqv = 3.2 gkg-1

Δ = 0.0 KΔv = 0.6 K

P4 (ATMOS) 2200 - 0330 UTC1-min Observations (86 km SSE of AB4)

Pre-Boundary Thermal Transition 2225

BoundaryPassage 2324-2359

Merged BoundaryPassage 0254-0313

ΔTd = 10.0 CΔqv = 4.6 gkg-1

Δ = -0.5 KΔv = 1.3 K

ΔTd = 8.7 CΔqv = 3.9 gkg-1

Δ = 2.9 KΔv = 2.2 K

P4 (ATMOS) 2319 – 0004 UTC θ (K), θv (K), qv (g kg-1), wind barbs

2324 2359Moisture Boundary Passage

qv

θv

θ

½ Barb = 2.5 ms-1

Full Barb = 5.0 ms-1

21 3 4 5 6

CO

NV

ER

GE

NC

E

CO

NV

ER

GE

NC

E

P4 (ATMOS) 0240 – 0318 UTC θ (K), θv (K), qv (g kg-1), wind barbs

0254 0313Moisture Boundary Passage

qv

θv

θPre-boundary convergence with slight cooling

½ Barb = 2.5 ms-1

Full Barb = 5.0 ms-1

6 panel MM1 transects

20:14:30 - 20:17:30 20:37:30 - 20:42:50 20:47:00 - 20:50:00 (N)

20:54:30 - 20:58:50 (N) 21:16:30 - 21:21:20 21:35:54 - 21:44:30

qv

θv

θ

1 2 3

4 5 6

T a

nd

Td

(°C

), M

ixin

g R

ati

o (

g k

g-1)

Te

mp

era

ture

(K

)

Time (UTC)

AMMOS 20:47:00 – 20:50:00 UTCθ (K), θv (K), qv (g kg-1), wind barbs

629 m

21 3 4 5

CO

NV

ER

GE

NC

E

CO

NV

ER

GE

NC

E

CO

NV

ER

GE

NC

E

CO

NV

ER

GE

NC

E

½ Barb = 2.5 ms-1

Full Barb = 5.0 ms-1

From Transect 3

ΔTd = 8.3 CΔqv = 3.7 gkg-1

Δ = 0.0 KΔv = -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 Td

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 Td

MB1

Elevated Residual Layer

* MB2 is 68 km SE of MB1

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

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

66

6

5

46

77

7

7

Terrain exaggerated in vertical

AB4

AB3

P1P2

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)

306

30530

4

303

302

301

300

301

302

303

304

301

302

303

300

• 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

P1P2

P3

‘x’ distance (km)

Aircraft Obs. (17:55:26 – 19:23:04) Virtual Potential Temperature (K)

303

304

302

302

301

305306

307

303304

305 304

303

302

AB4

AB3

P1P2

P3Terrain exaggerated in vertical

• 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)

‘x’ distance (km)

1.0 km GEM LAM

300

298

302

304

Pot. Temp.AscentDescent

T+7 hr forecast valid 2200 UTC along same axis used for aircraft analysis

306

308

310

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

1-1.5 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, 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)

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 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.

• 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