Examining the Role of Mesoscale Examining the Role of Mesoscale Features in the Structure and Features in the Structure and

Evolution of Precipitation Regions Evolution of Precipitation Regions inin

Northeast Winter Storms Northeast Winter StormsMatthew D. Greenstein, Lance F. Bosart, and Daniel KeyserMatthew D. Greenstein, Lance F. Bosart, and Daniel Keyser

Department of Earth and Atmospheric SciencesDepartment of Earth and Atmospheric SciencesUniversity at Albany, Albany, NY 12222University at Albany, Albany, NY 12222

David J. NicosiaDavid J. NicosiaNational Weather ServiceNational Weather Service

Binghamton Weather Forecast Office, Johnson City, NY Binghamton Weather Forecast Office, Johnson City, NY 1379013790

November 2, 2005November 2, 2005

OutlineOutline

• IntroductionIntroduction• Selection of cases Selection of cases • Precipitation patternsPrecipitation patterns• Data analysisData analysis• Preliminary resultsPreliminary results• Additional thoughtsAdditional thoughts• Future workFuture work

IntroductionIntroduction• Forecasters Forecasters cancan predict likely areas of precipitation predict likely areas of precipitation• Forecasters Forecasters cannotcannot always skillfully predict mesoscale always skillfully predict mesoscale precipitation signatures within these areas precipitation signatures within these areas• Forecasting mesoscale details adds value to a forecastForecasting mesoscale details adds value to a forecast• Precipitation patterns have multiple modes (forms)Precipitation patterns have multiple modes (forms)• Goal is to examine the three main ingredients …Goal is to examine the three main ingredients …

• MoistureMoisture• Stability RegimeStability Regime• Lifting MechanismLifting Mechanism… … that operate together to produce heavy snowthat operate together to produce heavy snow in a variety of modes in a variety of modes

Selection of CasesSelection of Cases• Cases occur in area bounded byCases occur in area bounded by 36.5°N, 50°N, 65°W, and 85°W36.5°N, 50°N, 65°W, and 85°W• Within U.S. radar coverage Within U.S. radar coverage • 1 October – 30 April 1 October – 30 April • No warm sector precipitationNo warm sector precipitation• P–type predominantly snow P–type predominantly snow • “ “Heavy snow” = 15+ cm in 12 h over an area the size Heavy snow” = 15+ cm in 12 h over an area the size of CTof CT• No lake effect snows and enhancementsNo lake effect snows and enhancements• Past three winters (2002–3, 2003–4, 2004–5)Past three winters (2002–3, 2003–4, 2004–5)

20 Cases20 Cases• 26–27 Nov 26–27 Nov 20032003• 4–6 Dec 20024–6 Dec 2002• 25–26 Dec 25–26 Dec 20022002• 2–5 Jan 20032–5 Jan 2003• 6–7 Feb 20036–7 Feb 2003• 15–18 Mar 15–18 Mar 20032003• 6 Mar 20036 Mar 2003

• 5–8 Dec 20035–8 Dec 2003• 13–15 Dec 13–15 Dec 20032003• 14–15 Jan 14–15 Jan 20042004• 27–28 Jan 27–28 Jan 20042004• 16–17 Mar 16–17 Mar 20042004• 18–19 Mar 18–19 Mar 20042004

• 19–20 Jan 200519–20 Jan 2005• 22–23 Jan 200522–23 Jan 2005• 24–25 Feb 200524–25 Feb 2005• 28 Feb–2 Mar 28 Feb–2 Mar 20052005• 8–9 Mar 20058–9 Mar 2005• 11–13 Mar 200511–13 Mar 2005• 23–24 Mar 200523–24 Mar 2005

Precipitation ModesPrecipitation Modes• UniformUniform• FracturedFractured• BandedBanded

– – Solid bands (with or without gaps between them)Solid bands (with or without gaps between them)– – Broken bandsBroken bands– – Band segmentsBand segments

• During a storm life cycle and even at one time,During a storm life cycle and even at one time, multiple modes may be present multiple modes may be present

• Blob-likeBlob-like• GrainyGrainy• UnclassifiedUnclassified

Precipitation Modes: Precipitation Modes: UniformUniform

Precipitation Modes: Precipitation Modes: Fractured / Band Fractured / Band SegmentsSegments

Precipitation Modes: Precipitation Modes: Broken BandBroken Band

Precipitation Modes: Precipitation Modes: FracturedFractured

Precipitation Modes: Precipitation Modes: Segments? Blobs? Segments? Blobs? Grainy?Grainy?

Data AnalysisData Analysis• 32–32–km North American Regional Reanalysis (NARR)km North American Regional Reanalysis (NARR)• How to evaluate the stability regime?How to evaluate the stability regime?

• Previous research: frontogenesis in the presence of Previous research: frontogenesis in the presence of weak weak moist symmetric stability yields moist symmetric stability yields bandsbands• Negative saturation equivalent potential vorticity Negative saturation equivalent potential vorticity (EPV*) (EPV*) indicates slantwise and/or upright instability indicates slantwise and/or upright instability• Upright dominates slantwise instabilityUpright dominates slantwise instability• Debate continues on EPV* or EPV*Debate continues on EPV* or EPV*• Stability diagnostic: EPV* < 0.25 PVUStability diagnostic: EPV* < 0.25 PVU

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Data Analysis: Data Analysis: Diagnostic plotDiagnostic plot• Depth of the EPV* < 0.25 PVU layer in hPaDepth of the EPV* < 0.25 PVU layer in hPa

• Examine 50 hPa layers above 850 hPa Examine 50 hPa layers above 850 hPa • [Number of layers] x 50 hPa = Depth[Number of layers] x 50 hPa = Depth

• CI overlayCI overlay• If saturation equivalent potential temperature (ΘIf saturation equivalent potential temperature (Θeses) ) decreases upward in a 50 hPa layer decreases upward in a 50 hPa layer

• 700 hPa Miller 2D frontogenesis overlay700 hPa Miller 2D frontogenesis overlay

• What does this diagnostic plot show for banding cases?What does this diagnostic plot show for banding cases?

Data Analysis: Data Analysis: 0000 UTC 26 Dec 20020000 UTC 26 Dec 2002

Data Analysis: Data Analysis: 0000 UTC 26 Dec 20020000 UTC 26 Dec 2002

Data Analysis: Data Analysis: 1500 UTC 5 Dec 20021500 UTC 5 Dec 2002

Data Analysis: Data Analysis: 1500 UTC 5 Dec 20021500 UTC 5 Dec 2002

Data Analysis: Data Analysis: 2100 UTC 14 Dec 20032100 UTC 14 Dec 2003

Data Analysis: Data Analysis: 2100 UTC 14 Dec 20032100 UTC 14 Dec 2003

Preliminary ResultsPreliminary Results• Examined first 13 cases (2002–3 & 2003–4 winters)Examined first 13 cases (2002–3 & 2003–4 winters)• No apparent correlation found between depth and No apparent correlation found between depth and modemode• Band seems to be associated with EPV* depth Band seems to be associated with EPV* depth gradientsgradients … but gradients still exist with other modes … but gradients still exist with other modes• Uniform: gradients, frontogenesis poleward of snow,Uniform: gradients, frontogenesis poleward of snow, almost no CI almost no CI• CI CI broken or fractured … but not the converse broken or fractured … but not the converse• Gradients not well defined for broken bands, band Gradients not well defined for broken bands, band segments, segments, and fractured modes and fractured modes• Fractured: no frontogenesis nearbyFractured: no frontogenesis nearby• Bands with spaces between them have at least some CIBands with spaces between them have at least some CI

Additional ThoughtsAdditional Thoughts• This diagnostic approach roughly works, but …This diagnostic approach roughly works, but … more ingredients are needed! more ingredients are needed!• EPV* alone is not sufficient! Neither is EPV* + EPV* alone is not sufficient! Neither is EPV* + frontogenesis!frontogenesis!• Combine Combine STABILITY REGIMESTABILITY REGIME and and MESOSCALE LIFTING MESOSCALE LIFTING MECHANISMMECHANISM (frontogenesis) with … (frontogenesis) with …

… … SYNOPTIC-SCALE LIFTINGSYNOPTIC-SCALE LIFTING MECHANISMSMECHANISMS… … MOISTUREMOISTURE (mean layer RH?) (mean layer RH?)… … MICROPHYSICSMICROPHYSICS (dendritic growth) (dendritic growth)

• Synoptic-scale forcingSynoptic-scale forcing• Warm advection Warm advection smoother smoother• Differential cyclonic vorticity advection Differential cyclonic vorticity advection more jagged more jagged

Future WorkFuture Work• Separate depths of weak moist symmetric stability (and Separate depths of weak moist symmetric stability (and

instability) and CI instability) and CI• Depth of weak moist symmetric stability layer that Depth of weak moist symmetric stability layer that satisfies satisfies omega and/or dendritic growth criteria omega and/or dendritic growth criteria• Depth of frontogenetical layer Depth of frontogenetical layer • Ratio of synoptic-scale forcingsRatio of synoptic-scale forcings• Various overlay combinations of synoptic-scale forcing, Various overlay combinations of synoptic-scale forcing, frontogenesis, EPV* < 0.25 depth, omega, and frontogenesis, EPV* < 0.25 depth, omega, and dendritic dendritic growth criteria growth criteria• Magnitude of EPV* < 0.25 depth gradientMagnitude of EPV* < 0.25 depth gradient• Further investigate any EPV* depth / mode correlationsFurther investigate any EPV* depth / mode correlations

Ultimate GoalUltimate Goal• Develop diagnostics for determining modes of heavy Develop diagnostics for determining modes of heavy snow snow based on… based on…

• Synoptic-scale and mesoscale forcingsSynoptic-scale and mesoscale forcings• Stability regimesStability regimes• MicrophysicsMicrophysics

• Similar to tables for modes of convectionSimilar to tables for modes of convection (wind shear and CAPE parameters) (wind shear and CAPE parameters)• Possibility of transforming diagnostic into a Smart Tool Possibility of transforming diagnostic into a Smart Tool for AWIPS for AWIPS

Special thanks to …Special thanks to …• David Ahijevych (NCAR) for making gridded WSI David Ahijevych (NCAR) for making gridded WSI NOWrad NOWrad composite data available composite data available• Anantha Aiyyer (UAlbany) for help with FORTRAN Anantha Aiyyer (UAlbany) for help with FORTRAN scripts to scripts to work with gridded NARR data work with gridded NARR data

Questions? Comments?Questions? Comments?

e-mail: greenstein@atmos.albany.edue-mail: greenstein@atmos.albany.edu