1997-1998 FIELD TEST
Steven M. Zubrick
Steven J. Weiss
The System for Convection Analysis and Nowcasting (SCAN) described by Smith et al. (1998) is an integrated suite of multi-sensor applications which detects, analyzes, and monitors convection and generates short-term probabilistic forecast and warning guidance for severe weather and flash floods automatically within the National Weather Service's (NWS's) Advanced Weather Interactive Processing System (AWIPS). The goals of SCAN are:
- to provide forecasters with accurate, timely, and consistent severe weather and flash flood guidance,
Corresponding author address: S. Smith, TDL/NWS, SSMC2, 1325 East-West Hwy., Silver Spring, MD, 20910 (Stephan.Smith@noaa.gov)
- to develop "smart" computer displays, menus,
and graphical user interfaces that optimize the
utility of the AWIPS Display 2 Dimensions
(D2D; Biere 1998) and are compatible with the
warning decision process,
- to develop multi-sensor databases to support
the verification of thunderstorm, severe
weather, and flash flood forecasts/warnings,
- to supplement forecaster event monitoring with
multi-sensor, automated event monitoring,
- and, to accelerate the rate of technology transfer from research to operations.
Operational implementation of SCAN will
result in longer lead times on warned events,
fewer missed events, increased forecaster situational awareness, reduced forecaster fatigue
during warning situations, rapid improvement in
implemented techniques, and a well-defined focus
for applied research.
During the 1997 and 1998 convective
seasons, a SCAN prototype consisting of the
National Severe Storms Laboratory's (NSSL's)
Warning Decision Support System (WDSS), the
National Center for Atmospheric Research's
(NCAR's) Thunderstorm Autonowcaster and the
AWIPS Thunderstorm Product/1-hr Quantitative
Precipitation Forecast (QPF) was tested at the
NWS forecast office in Sterling, Virginia. The
purpose of the field test was to integrate the
above software applications and to examine the
usefulness of their combined products as tools for
forecasters responsible for short-term forecasts
and warnings. The Storm Prediction Center
(SPC) provided probabilistic Day-3 convective
outlooks (Hovis et al. 1998) for the SCAN test
area primarily to assist in travel planning and
staffing coordination for the larger convective
This paper describes the functionality of the
SCAN prototype and the preliminary findings of
the field tests as they pertain to severe weather
and flash flood warnings. Additional information
on the SCAN field tests, the SCAN AWIPS development schedule, and other SCAN-related items
is available from the SCAN homepage at
2. SCAN PROTOTYPE
The Research and Applications Program
(RAP) of NCAR has over the past several years
developed and refined an integrated system
designed to produce automated guidance on the
detection, tracking, and short-period (0-30 min)
forecasting of thunderstorms. The system is
conceptually based on a large compendium of
operational and modeling research acquired over
the years on the nature of convective storms.
The complete Thunderstorm Auto-Nowcast
(TAN) system (Mueller et al. 1997) is comprised
of about half a dozen major sub-systems and is
designed to integrate and process data from
various data platforms (radar, satellite, upper-air
soundings, surface mesonet, etc.) using
sophisticated algorithms for feature detection and
tracking. These processed data are combined with
boundary layer model output and heuristics of
thunderstorm extrapolation and trending to produce
area-specific, short-period (0-30 min) forecasts of
convection (defined to be where radar echoes of
35 dBz will be located).
Similarly, NSSL has maintained a long-term
effort to develop algorithms that utilize integrated
meteorological data to identify severe weather
phenomena. In support of these applications,
NSSL has also designed and implemented new
concepts for displaying critical information used in
the warning decision process. The combined
(algorithms and display) system, called the Warning Decision Support System (Eilts 1997), has
been tested operationally for several years at
selected NWS offices across the United States.
Over the past several years, the NWS's
Techniques Development Laboratory (TDL) has
engineered both algorithms and software applications focused on the diagnosis and prediction of
thunderstorms, severe weather, and heavy precipitation. Two of the more recent of these, the AWIPS
Thunderstorm Product (Churma and Smith 1998)
and 1-hr Quantitative Precipitation Forecast (QPF),
were chosen for testing within the SCAN prototype.
The former provides automated thunderstorm
detection at fixed geographic locations, while the
later generates probabilistic 60-min forecasts of
precipitation based on an extrapolative-statistical
approach (Kitzmiller 1996).
Since WDSS was designed with warning
decisions in mind, and we are principally exploring
issues related to the implementation of new guidance products to assist forecasters in making
warning decisions, WDSS was chosen as the
vehicle on which the integration of all applications
would take place. In the case of the TAN, all the
various sub-systems ran on independent hardware
and only a selected subset of the output was
displayable on WDSS (the complete TAN output
was available to the forecasters on the independent TAN workstation). For the Thunderstorm
Product and the 1-hr QPF, however, the software
was completely integrated into WDSS.
From a conceptual standpoint, WDSS and
Thunderstorm Product components of the system
provide detection and monitoring of severe and
non-severe thunderstorms. The TAN and 1-hr
QPF provide a limited predictive capability (as a
necessary step in generating its forecasts, however, the TAN also detects boundaries and growing cumulus clouds).
Fundamentally, we hope to explore the utility of combining the basic information provided by "automated severe thunderstorm detection and monitoring" with that of "automated thunderstorm nowcasting" in order to improve the warning decision process. The linkage of these two key functionalities within AWIPS could provide the basis for an automated, "suggested" severe thunderstorm warning area.
Significant enhancements to WDSS and TAN occurred in 1998. Most notably, an automated anvil tracker based on GOES infrared satellite data (Zaras and Rabin 1998) and the Area Mean Basin Estimated Rainfall (AMBER; Jendrowski and Davis 1998) algorithm were added to WDSS. The full suite of TAN applications including a satellite-based cumulus detection algorithm, a correlation radar echo area tracker, an ingest of surface mesonet data, and an adjoint numerical model were implemented in 1998. As of this writing, the 1998 field test was not complete and therefore the findings reported here are based only on our limited experience from late summer of 1997. Initial results from the 1998 field test will be presented at the conference.
3. SUMMARY OF 1997 OPERATIONS
The WDSS component of the SCAN prototype was installed in May, with all staff forecasters trained on its use by the end of June. The Thunderstorm Product, 1-hr QPF ,and limited version Thunderstorm Auto-nowcaster components were installed in July, with all forecasters receiving additional training by mid-August. The integrated SCAN evaluation lasted from mid-August through the end of September, which unfortunately, for the purpose of the test, coincided with an extremely quiet period of convective weather across the Mid-Atlantic Region.
4. PRELIMINARY FINDINGS
A post-'97 field test survey of the Sterling
forecasters indicated that the most-used products
in the SCAN prototype were (grouped by application):
- Cell table
- Mesocyclone table
- Reflectivity cross sections
- Time history trends (especially cell and mesocyclone trends)
- Animation of various 88D graphics
- Tracking Radar Echoes by Correlation (TREC) 2-dimensional wind fields
- Boundaries (detection and extrapolation)
- 30-min forecasts of thunderstorms
- Probabilistic 1-hr QPF of > 1.00 in.
Viewed as an integrated system, the SCAN
prototype was favorably received by the
forecasters. Most of the initial feedback focused
on ways that the utility of the TAN could be enhanced, both in the SCAN prototype itself and
eventually in AWIPS. All forecasters liked having
access to boundary detection/extrapolation information. The ability to overlay these products on
standard radar products was deemed to be highly
desirable. The Sterling staff felt the 30-min forecasts of thunderstorms would be useful in the
warning decision process, but also expressed a
desire for 60- or 120-min forecasts as a tool for
the short-term or public forecaster. No other
product generated as much excitement as the
TREC 2-dimensional wind field from the TAN. The
forecasters really felt this product helped them
locate areas of convergence (divergence) and
wanted it added immediately to the SCAN prototype display (it was not included originally). Although the lack of convective activity precluded
the evaluation of the SCAN prototype as a tool for
flash flood warnings, Sterling forecasters did find
the probabilistic 1-hr QPF of > 1.00 in to be useful
when heavy precipitation cells were detected by
SCAN participants (both research and
operational meteorologists) found the probabilistic
Day-3 convective outlooks provided by SPC to be
useful in alerting for the potential of a major convective event. Users found that the most useful
information was obtained from comparing the latest
Day-3 with the previous Day-3's and with the
climatological probabilities. In other words,
lacking an innate feel for the absolute probabilities, the meteorologists quickly applied a personal
calibration to them and, in this manner, derived
value from the forecasts.
In general, it is clear that the SCAN 1997-1998 Field Test has been an extremely useful
exercise for all parties involved. The NWS operational forecasters at Sterling were exposed to a
number of state-of-the-art forecasting/warning
tools that are targeted for implementation on
AWIPS. The meteorologists and developers at
NSSL, NCAR, TDL, and SPC were given the
opportunity to test experimental applications and
forecast products in a real-time operational environment. In so doing, they will be able to modify
and enhance these applications in a manner that
best lends itself to how the operational forecasters
perform their jobs in the modernized NWS.
The authors would like to thank the
programmers and meteorologists at TDL, NSSL,
and NCAR for their skilled work in programming
and developing the SCAN prototype. We would
also like to thank the forecasters and operational
staff at Sterling for their cooperation and assistance in organizing and carrying out the 1997-98
field test. The SPC outlook forecasters are
gratefully acknowledged for the their professional
expertise in preparation of the SCAN Day-3
convective outlooks. SCAN is funded by the
NWS, the National Science Foundation, and the
U.S. Weather Research Program.
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