Visually Enhanced Composite Charts for Severe Weather Forecasting and Real-time Diagnosis Josh Korotky NWS Pittsburgh PA NROW Annual Meeting 2002

Agenda  Composite Chart Approach and Diagnostic Templates  A Case study  LES 4 Panels  Cyclogenesis 4 Panels  GFS

The real atmosphere has great difficulty simulating the model atmosphere… …many good forecasts will continue to be ruined by atmospheric error! The Forecaster’s Paradox

Motivation  Due to the growing volume of available data…  …and the time intensive process of generating / disseminating forecast and warning products…  …it is critical that forecasters extract relevant information quickly before and during severe weather forecast and warning operations  Diagnostic and forecast methods that use visualization to highlight essential physical processes … Promote a better (and quicker) understanding of the real-time potential Allow forecasters to better anticipate the most probable range of convective evolutions for a given environment

Composite Chart Approach  Effective composite charts: Highlight important information….not all information Reveal the physical processes that promote severe storm development, convective organization, and storm mode Lead to quick recognition of the convective potential  Composite chart contents include: Measures of instability and vertical wind shear 3D moisture content, distribution, and availability Synoptic and mesoscale forcing mechanisms  Charts are enhanced visually by managing colors, images, and contours

Evaluating the Convective Potential IngredientDiagnostic Moisture Moisture Flux (role of LLJ) Specific Humidity Dew Point PW Layer RH Theta-e / Theta-e advection Instability CAPE, LI Large Scale Lift / ForcingModel Omega / -Div Q Mesoscale ForcingMoisture Flux Convergence Topographic forcing Frontal forcing / Frontogenesis Vertical Wind Shear Storm-relative Helicity Low – level and deep shears EHI, VGP Pressure MSLP, Pressure tendency

Composite Chart Model Diagnostic Templates

MSL Pressure * Best Lifted Index < 0 Surface Dew Points > xx o F Specific Humidity PW > x.x inches * BL Moisture Flux Convergence mb Moist Flux Conv Moisture Flux / Flux Magnitude Theta-e / Theta-e Advection * 2D Frontogenesis Potential Temperature Surface Wind EHI Index *0-1km / 0-3km AGL CAPE *0-1km / 0-3km AGL SR- Helicity Convective Inhibition 0-1km / 0-3km Normalized Shear 0-6km Normalized Shear Low – level Features

Upper – level Features 850mb Height / Temp *850mb Isotachs 850mb Wind Barbs 500mb Height / Temperature *500mb Isotachs 500mb Wind barbs DivQ MSLP *Accumulating Precipitation / mb RH 250mb Height / Wind Barbs 250mb Isotachs mb Mean Wind mb Mean Divergence mb/ mb Omega

MSL Pressure and METARS * Best Lifted Index < 0 Surface Dew Points > xx o F PW > x.x inches * BL Moisture Flux Convergence mb Moist Flux Conv Moisture Flux / Flux Magnitude K-Index BL Theta-e / Theta-e Advection * 2D Frontogenesis Potential Temperature Surface Wind EHI Index *0-1km / 1-3km AGL CAPE *0-1km / 1-3km AGL SR- Helicity Convective Inhibition 0-1km / 1-3km Normalized Shear Deep Normalized Shear RUC Analysis

A Case Study  Highlights a severe convective wind event that effected parts of Ohio, Pennsylvania, West Virginia, New York, and Maryland on 9 March 2002  Composite charts of model forecast fields (Eta) are supplemented with composite charts of hourly RUC surface analysis Eta for evaluating large scale convective potential Hourly RUC provides a critical link to the model forecasts

850mb Wind (kt) and Normalized Vcomp Wind Anomaly 08/12 UTC Eta: 33hr Forecast Valid 3/9/ UTC 4 – 4.5 SD

850mb Wind and Normalized Vcomp Wind Anomaly 27hr Forecast Valid 3/9/ UTC > 4.5 SD

Upper and Low-level Features  33, 21, 9 hr forecasts valid at 21 UTC 9 March

Upper-level Features - 08/12 UTC Eta 33hr Forecast Valid 3/9/ UTC

Low-level Features - 08/12 UTC Eta 33hr Forecast Valid 3/9/ UTC

Upper-level Features – 09/00 UTC Eta 21hr Forecast Valid 3/9/ UTC

Low-level Features – 09/00 UTC Eta 21hr Forecast Valid 3/9/ UTC

Upper-level Features – 09/12 UTC Eta 9hr Forecast Valid 3/9/ UTC

Low-level Features – 09/12 UTC Eta 9hr Forecast Valid 3/9/ UTC

Summary of the Large Scale Potential Successive runs of the Eta indicate:  Deep layer of strong flow 65 – 70 kts at 850mb over Ohio Valley  Significant vertical wind shear associated with vigorous low- level jet SRH 400 – 500 m 2 s 2 0-3km normalized shear >.014 s -1  Moderate moisture Warm sector surface dew points 55 – 57 o F  Narrow layer of deep moisture Potential for cloud breaks ahead of front Destabilizing potential

Summary of the Large Scale Potential  Considerable low-level forcing Strong moisture flux convergence Strong frontogenesis along a vigorous frontal system  Significant pressure rise/fall couplet indicates deepening/dynamic system 10mb/3hr pressure rises behind front 8mb/3hr pressure falls ahead of front  But….only marginal instability CAPE forecast to remain less than 500 jkg-1 Best Lifted Index (BLI) expected to reduce no further than -2

A Range of Expectations  Expectations Strong linear forcing will promote a narrow low-topped squall line Isolated/scattered wind damage the primary threat … unless the real-time environment destabilizes more than indicated  The real time challenge Do observations / RUC / LAPS analysis indicate greater instability? Greater instability would indicate more widespread severe potential

Real Time RUC Surface Analysis 3/9/02/ 18 UTC – 3/9/02/ 21 UTC Linking the model forecast to real-time events…

18 UTC RUC Analysis

19 UTC RUC Analysis

20 UTC RUC Analysis

RUC / Observational Summary at 20 UTC  The moisture, forcing, vertical wind shear, pressure pattern, and pressure tendency substantiate initial expectations…  The environment has destabilized more than expected !!  Observations Winds gusting mid 30s kts ahead of front Radar indicated a developing low-topped narrow squall line Reports from CLE and ILN indicated wind gusts > 80 mph and wind damage associated with convective line  New Expectations With indications of greater instability and real-time reports… Damage is going to be widespread rather than scattered/isolated Damage will be from winds…low probability of tornadoes

23 UTC Radar and Satellite

Conclusions  A narrow, low-topped squall line produced significant wind damage throughout the NWS PBZ CWA  Forecast (Eta) and diagnostic (RUC) methods that combine science and visualization… Allowed forecasters to better anticipate the most probable range of convective evolutions before the event Promoted a better (and quicker) understanding of the changing convective potential during the event Contributed to more effective warning decisions.

LES 4 Panels

Model Run Snow Accum Model Run Accum Precip * mb/ mb RH Ptype Likely Icons mb Lapse Rate * LR / mb LR BL Moisture Flux Convergence mb Moist Flux Conv mb Thickness * mb/ mb Fgen Potential Temperature MSLP Surface Wind mb Tadv Sfc Td Specific Humidity *Topo Omega / mb Omega 900mb Wind 900mb Streamlines Low – level Features

Low-level Features – Valid 00 UTC

Low-level Features – Valid 12 UTC

Cyclogenesis 4 Panels

Upper-level Features – Valid 21 UTC 16 Oct 2002

Low-level Features – Valid 21 UTC 16 Oct 2002

GFS