High-Resolution Simulations of the 25 December 2002 Banded Snowstorm using Eta, MM5, and WRF

David NovakNOAA/ NWS Eastern Region Headquarters, Scientific Services Division, Bohemia, New York

Brian ColleUniversity at Stony Brook, State University of New York, Stony Brook, New York

Daniel KeyserUniversity at Albany, State University of New York, Albany, New York

25 December 2002 Snowstorm

Conceptual Models

Novak et al. 2004 Moore (2003)

Synoptic Environment Frontal Environment

Motivation• Can high-resolution models simulate the physical

processes responsible for mesoscale banding?

• What is the simulated relationship between the modeled band and frontogenesis, weak moist symmetric stability (MSS), moisture, and ascent?

• Does precipitation drift influence the forecast band location?

• What are the predictability limits of mesoscale banded features?

Case Study Design• 25 December 2002 Banded Snowstorm:

– Compare Eta, MM5, and WRF forecasts to observations– Models initialized at 0000 UTC 25 Dec 2002

Model Resolution Convection Boundary Layer

Micro-physics

FSL RUC 20 km Grell–Devenyi Burk– Thompson

Simple Ice

NCEP Eta 12 km BMJ Mellor–Yamada (MY)

Ferrier

NCAR PSU MM5

12 km Grell MRF Simple Ice

NCAR WRF v2.0

12 km Grell–Devenyi YSU Simple Ice

25 December 2002 SnowstormLow Track Comparison

25 December 2002 Snowstorm

MSLP Time Series

960

965

970

975

980

985

990

995

1000

12Z 15Z 18Z 21Z 00Z 03Z 06Z

Time (UTC)

MS

LP

(m

b) Obs

Eta

MM5

WRF

QPF Performance1200 UTC 25 Dec – 1200 UTC 26 Dec QPF

ObsMax = 3.00 in.

EtaMax = 1.50 in.

MM5Max = 1.85 in.

WRFMax = 2.25 in.

RUC Analyses

• Radar Reflectivity • 700-hPa Miller 2D Frontogenesis [thin solid; ºC (100 km)–1 (3 h)–1 ]• 700-hPa Geopotential Height (thick solid)

RUC Cross Section

• Frontogenesis (shaded)

• Өes (solid)

• EPVf* = 0 PVU (green)

• Relative Humidity (shaded)

• Vertical Velocity (dashed; µb s-1)

Eta Forecast

• 3-h Accumulated Precip (shaded; hundreths in.)• 700-hPa Miller 2D Frontogenesis [thin solid; ºC (100 km)–1 (3 h)–1 ]• 700-hPa Geopotential Height (thick solid)

Eta Cross Section

• Frontogenesis (shaded)

• Өes (solid)

• EPVf* = 0 PVU (green)

• Relative Humidity (shaded)

• Vertical Velocity (dashed; µb s-1)

MM5 Simulation

Reflectivity

Frontogenesis

Ө

Circulation

EPVf*

< 0

Өes

Circulation

WRF Simulation

Reflectivity

Frontogenesis

Ө

Circulation

EPVf*

< 0

Өes

Circulation

Relationship between the Band, Frontogenesis, weak MSS, and Moisture

MM5 WRF

2000 UTC2000 UTC

Precipitation Drift?

After 2200 UTC

•30 dBZ core of band tilted towards SE

•height of 30 dBZ core steadily descends

2100 UTC2200 UTC2300 UTC0000 UTC0100 UTC0200 UTC0300 UTC

ENX ENX

Precipitation Drift?

Schenectady (SCH) Wind Profiler

Using SCH winds at 2200 UTC, assuming crystal fall speed of ~1 m s-1 and steady-state conditions:

Crystal drifts 46.3 km @ 222°

Findings• Eta/MM5/WRF capable of simulating mesoscale band

formation and dissipation

• All three model forecasts showed a narrow sloping ascent maximum associated with strong midlevel frontogenesis and weak moist symmetric stability

• Model QPFs were underdone by as much as 50% in the banded region, and exhibited a southeast position error.

• Slantwise ascent and precipitation drift may account for slight displacement (20–40 km) between frontogenesis maximum and band

• Despite different surface cyclone intensities, all three models predicted band formation, suggesting some predictability in this case

Future Work• Explore why all three model forecasts exhibited a southeast position error and dissipated the band too early

• Diagnose 3D hydrometeor trajectories across the band

• Perform higher-resolution (4 km / 1.33 km) model runs

• Use high-resolution ensembles to explore mesoscale banding predictability in this case

Ensembles

WRF Eta Init Grell–Devenyi / YSU Simple Ice

MM5 Eta init Grell / MRF Simple Ice

MM5 GFS init Grell / MRF Simple Ice

MM5 Eta init Grell / GS Simple Ice

MM5 Eta init KF / MRF Simple Ice

MM5 Eta init Grell / MRF Reisner

WRF Eta Init KF / YSU Simple Ice