1. Evaluation of Convective Storm Initiation Nowcasts and Forecaster Involvement
60 min Nowcasts
60 min Verification
Cold Front
Regime
Rita Roberts, Amanda Anderson, Barbara Brown
National Center for Atmospheric Research
WMO WWRP Workshop on Use of NWP for Nowcasting
Boulder, Colorado
26 October 2011

2. Challenges in Nowcasting Convective Initiation
Difficult to accurately predict the timing and location of convective storm initiation.
Numerical models are not able to routinely and accurately provide site-specific nowcasts of convective storms on the short 1-2 hr time frame.
In the interim, forecasters and heuristic systems can provide the rapidly updated, high-resolution, spatio-temporal nowcast products needed by aviation and other end-users.

3. Forecaster-Over-the-Loop AutoNowcaster Demonstration NWS and NCAR
AWIPS Display
1 hr nowcasts
6 min updates
2 km grid
14 radars
Satellite
Soundings
Surface stations
NWP RUC output
VDRAS fields
Forecaster input
Dallas/Ft. Worth WFO
Thunderstorm Initiation Nowcast Field
See Nelson et al paper, this conference

4. FOTL AutoNowCaster (ANC) system was demonstrated at the National Weather Service Dallas/Ft. Worth WFO from
Goals:
Improve the consistency, reliability, and accuracy of one hour convective storm nowcasts for inclusion in automated aviation weather digital products (NextGen 4-D data cube).
Assess NWS forecaster involvement in providing value-added enhancements to gridded, automated ANC products for NextGen.

5. The Federal Aviation Administration NextGen 4-D Weather Cube:
Provides a common weather picture for the National Air Space
by 2025
Observations
Forecasting
Numerical
Modeling
Systems
Satellites
Network Enabled Operations
Statistical
Forecasting
Systems
NWS
Forecaster
Radars
Data Integration
4D Wx Cube
Aircraft
4D Wx
SAS
Automated Forecast
Systems
Surface
Forecast Integration
Soundings
Grids
Decision
Support
Systems
Custom
Graphic
Generators
Custom
Alphanumeric
Generators
Integration into User Decisions

6. What is needed to meet the NextGen requirements - and be successful??
High resolution observations
Boundaries, winds, stability, gravity waves, capping inversions, elevated dry layers, moisture variability and gradients
NWP
- high resolution data assimilation for boundary layer winds and precipitation forecasts
- frequent update cycle
- at least 1 hr analysis and forecast fields
- ability to represent multiple scale interactions
- accurate output fields (CAPE, CIN, RH, vertical shear, convergence,
vorticity, temperature gradients)
Forecaster
- convergence boundary locations
- climatology data base
- conceptual models and documented weather regimes
- QC of final products
Basic understanding (most important)
Of elevated convection, secondary convection, outflow characteristics

7. Operational Role of Forecaster with the ANC system
Entering convergence boundaries periodically during shift
Nudging storm initiation nowcast fields based on
forecaster understanding of NWP performance, the observations and their experience.
Specification and selection of weather regime

8. Storm initiation likelihood fields for different synoptic regimes
Dry Line Regime
Air Mass Regime
7 different regimes (fuzzy-logic rule sets ) available
cold front, warm front, dryline, air mass, MCS, no storms, and mixed (default) regimes
Developed in collaboration with NWS forecasters
User Selectable

9. RUC NWP Model Forecasts “Too Hot” or “Too Cold”
Forecaster has sliding scale toolbar to adjust (nudge) thunderstorm initiation likelihood values over the whole domain - +

10. Challenges in Evaluating the Performance of Convection Initiation Nowcasts
Difficult to validate forecasts of these “rarer” convective initiation events.
Evaluation is hampered by the impacts of large-scale storm characteristics as well as small-scale errors in timing and location.
Difficult to statistically highlight the impact of human forecaster on an automated nowcast system.

11. Methodology for Evaluation
Focus the evaluation on small regions rather than the broader ANC domain.
Stratifying cases into similar forcing categories (i.e., weather regimes).
Examination of time-series performance for specific cases.
Use of contingency table performance diagrams to simultaneously investigate changes in multiple forecast performance attributes.

12. 44 days analyzed in great detail
FWD CWA and ANC Domain
Multiple Radar Reflectivity Mosaic
Forecaster-entered boundary
4 Year Period
Evaluated
( )
44 days analyzed in great detail
ANC Convective Storm Initiation
60 min Nowcast Field
ANC Final 60 min Nowcast Field: Initiation, Growth & Decay

13. Statistics Over Whole ANC Domain
Convective storm initiation period

14. Calculating Statistics Over Sub-Domains
Evaluation of nowcasts on the scale of the phenomena being nowcast.

15. Forecaster Interaction with ANC System
19:21 UTC
20:21 UTC
21:21 UTC
4 July 2006
Cold Front Regime
Black contours: Location of > 35 dBZ storms at validation time

16. Time-Series Plots – 4 July 2006
for selected sub-domain boxes

17. for all sub-domain boxes
Summary Histograms of Change in Verification Scores With and Without Human Input
for all sub-domain boxes
4 July 2006

18. Performance Diagrams* 4 July 2006
*After Paul Roebber, Clive Wilson
Forecaster-entered convergence boundaries have largest impact on convection initiation nowcasts.
Examining only those domains that contain boundaries allows us to analyze change in nowcast accuracy due to forecaster involvement.

19. Performance for 27 August 2006

20. 24 April 2007
12 May 2007
1 August2007
8 October 2007

21. 8 October 2007
Mixed Regime

22. 30 July 2008 25 March 2009 10 June 2009 MCS Regime Warm Front Regime
Cold Front Regime

23. Summary
PODs of new storms increased by 20-60% with little or no change observed in false alarm ratios.
Bias values increased from to with human involvement.
Range of CSI values increased from (ANC) to (FOTL-ANC).
Values of CSI as large as 0.6 were observed.
A true improvement of the nowcast performance was achieved through forecaster involvement.
Forecasters played an important role in improving the quality of automated, high-resolution, gridded, convective initiation nowcasts for end-users.