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

Ingredient Diagnostic

Moisture Moisture Flux (role of LLJ)Specific HumidityDew PointPWLayer RHTheta-e / Theta-e advection

Instability CAPE, LI

Large Scale Lift / Forcing Model Omega / -Div Q

Mesoscale Forcing Moisture Flux ConvergenceTopographic forcingFrontal forcing / Frontogenesis

Vertical Wind Shear Storm-relative HelicityLow – level and deep shearsEHI, VGP

Pressure MSLP, Pressure tendency

Composite Chart Model Diagnostic Templates

MSL Pressure

*Best Lifted Index < 0

Surface Dew Points > xxo F

Specific Humidity

PW > x.x inches

*BL Moisture Flux Convergence

1000-850mb 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 /

1000-850mb RH

250mb Height / Wind Barbs

250mb Isotachs

850-300mb Mean Wind

300-200mb Mean Divergence

1000-850mb/700-500mb Omega

MSL Pressure and METARS

*Best Lifted Index < 0

Surface Dew Points > xx o

F

PW > x.x inches

*BL Moisture Flux Convergence

1000-850mb 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

3/9/02 - 21 UTC

4 – 4.5 SD

850mb Wind and Normalized Vcomp Wind Anomaly

27hr Forecast Valid 3/9/02 - 21 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 3/9/02 -

21 UTC

Low-level Features - 08/12 UTC Eta 33hr Forecast Valid 3/9/02 -

21 UTC

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

Valid 3/9/02 - 21 UTC

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

Valid 3/9/02 - 21 UTC

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

Valid 3/9/02 - 21 UTC

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

Valid 3/9/02 - 21 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 m2s2 0-3km normalized shear > .014 s-1

Moderate moisture Warm sector surface dew points 55 – 57oF

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 Analysis3/9/02/ 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

*1000-850mb/1000-500mb RH

Ptype Likely Icons

850-700mb Lapse Rate

*1000-850 LR / 850-700mb LR

BL Moisture Flux Convergence

1000-850mb Moist Flux Conv

1000-850mb Thickness

*1000-950mb/850-700mb

Fgen

Potential Temperature

MSLP

Surface Wind

1000-850mb Tadv

Sfc Td

Specific Humidity

*Topo Omega / 700-500mb Omega

900mb Wind

900mb Streamlines

Low – level Features

Low-level Features – Valid 00 UTC

Low-level Features – Valid 00 UTC

Low-level Features – Valid 12 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