# Presentation: 694250

## A Severe Weather Proxy Developed from the NOMADS Real Time Data Base of an Operational Model

** **

- Jordan C. Alpert  		_[jalpert](mailto:jalpert@ncep.noaa.gov)__[@ncep.noaa.gov](mailto:jalpert@ncep.noaa.gov)_
- Jun Wang/SAIC		jun.wang@noaa.gov

**where the nation’s climate and weather services begin**

- EMC

- 21st Conf on IIPS, 18.4, 85 Annual AMS Meeting, 9-13 January 2005, San Diego, California

- NCEP/Environmental Modeling Center

## Motivation for a Severe Weather Proxy from an Operational NCEP Numerical Weather Prediction (NWP) Model

- Highest resolution Operational NWP model is not able to resolve severe weather causing phenomena that forecasters need to make accurate predictions.  This is because of the ...
- Lack of horizontal and vertical scale resolution for observations and models with sufficient detail and physical knowledge.
*Severe weather:*
- Tornado, damaging winds >50kts or hail >3⁄4” (SPC web page)
- Resulting from severe or organized convection,
- Thunderstorms, super cells, squall lines, multi-cell complexes
*An array of indicators is used by forecasters to analyze severe weather potential at or near observation time and from forecasts:*
- Lifted Index, Storm Relative Helicity, CAPE, Vertical profiles of weather elements such as temperature, dew point and wind....

*There are difficulties with NWP models predicting severe weather such as:*

## A challenge in reducing the severe weather risk: To improve the utilization of model output signatures of severe weather. 

- Wind convergence patterns,
- Often along frontal boundaries,
- Genesis of complex systems along fronts,
- Vorticity advection and vertical motions,
*Often occurring at scales of motion that are barely resolvable by models and may have difficulty reproducing the convection details.*
- For example:
- Qualitatively the vertical extent of convergence patterns associated with severe weather appears to grow and be advected vertically.
- We can not observe this phenomena directly.
- We suggest that the volume, shape or vertical extent of the 3-D convergence patterns from forecast models is a signature for sub-grid scale convective outbreaks.
-  *This was noticed by viewing Vis5D 3-D displays of model convergence patterns.*

*Models represent (simulate) very well dynamic and physical processes:*

## Interactive Visualization of Animated 3-D Model Data

- In a previous report (19th Conf on IIPS 15.2, AMS) it was shown that convergence pattern signatures and other 3-Dimensional displays were unique and useful, compared to 2-Dimensional ones.
- Display Three-Dimensions (D3D), Szoke, et. al., 2001 software available for Advanced Weather Interactive Processing System (AWIPS) under test for forecasters at some Weather Forecast Offices.
- Using Vis5D, “visualization 5-dimensional”, meaning 3 space, time and variable space, is an interactive visualization system created at the University of Wisconsin (Hibbard, 1994).
- In use by the science, educational and by the atmospheric science and NWP model research community as well as other display systems.
- Can View renderings of “Iso-surfaces” of convergence patterns.
*The basic visualization capabilities of these systems are similar as D3D was created from Vis5D. *

## 3-dimensional rendering of the 21-hr NCEP Operational forecast of convergence >3X10-5 s-1 a yellow iso-surface from IC of 00Z 17SEP2004

## A Model Severe Weather Proxy

*Convergence calculated from the motion fields of the NCEP Global Forecast System*
- Test that the model associates these convective areas with severe weather according to vertical extent, shape and volume.
- Can the proxy distinguish between events with no severe weather?
*Need to define a precise criteria:*
-  Define a convergence amplitude criteria,
-  Define a vertical extent as number of vertical levels between the surface and 500 mb where convergence amplitude criteria is met.
*Qualitatively the convergence patterns grow in vertical extent in proportion to increased precipitation, winds, decreased surface pressure.  The NWP model may advect the convergence patterns upward in response to unresolvable meso-scale phenomena.  *

## Verification

- The Watch means that severe weather has potential in an area usually over a few hours,
- The Watch is a manually prepared _prediction _from conventional and non-conventional observations such as radar and RAOB soundings.
- The Warning means that severe weather is known to have occurred in an area.
- A Watch or Warning consists of a text file indicating the location by  latitude and longitude pairs outlining a polygon area of severe weather potential typically 25,000 square miles.
- The often used model forecasts of “Best” Lifted Index, where negative values less than –4 are considered an indicator of potential severe thunderstorms, will also be verified with watch box locations as a comparison.
*Watch and Warning box areas will be used as the verification area.  Forecasted patterns meeting a convergence criteria will be considered a success (Hit) if it is forecast within the Watch or Warning box.*

*A convenient verification for objectively locating observed severe weather *
*is the NCEP Severe Storms Prediction Center (SPC) Severe Weather Watch *
*or Warning Box. *

## Convergence pattern (X10-5 s-1) at 1000mb for 17SEP04 21-h forecast and the SPC Watch box (in black, middle Atlantic location) valid at the same time and over the next 3 hours.  The verification area of interest is shown in red. 

## Accessing the Data Using NOMADS servers

- Using the NOMADS OPEN-DAP/DODS server to download the GFS model run history, including unpacking the model GRIB files and organizing projection/location information.
- This is done using constrained queries to the server of the form: http://nomad2.ncep.noaa.gov:9090/dods/gfs/archive/gfs20040917/gfs/_00z.ascii?vgrd10m[7:7][110:140][235:300]
- Replacing vgrd10m with vgrd would include the vertical wind profile.
- [7:7] indicates the seventh forecast time (3-hr intervals) or 21z.
- [110:140][235:300] are the grid points used in the eastern US domain chosen to encompass inclusively an area where severe weather often occurs.  The region under consideration starting with 110 is 100 degrees north of the south pole and 235 represents 235 degrees east of 0° meridian for a 30 by 65, over 1200 grid point area.

*The NOMADS real time server was used to obtain the wind fields *
*needed to calculate the convergence as well as the lifted index.*

## Results of the Automated Convergence Verification Program

- Many large distance errors in the location of the severe weather box indicate a high false alarm rate.
- When the convergence criteria for severe weather is met, but the verifying distance exceeds 1000 km, then the result does not apply (N/A) as there may be synoptic weather from another system. This is also done for the lifted index indicator.
- Six criteria C1-C6 are chosen for the convergence calculation for location and vertical extent.
- When the convergence criteria is met the data is distributed into 6 accuracy categories: Hits, <100 km, 100-200 km, 200-300 km >300 km and N/A, as described above.

*The verification program considers the distance from forecasted *
*locations to the nearest point within the watch box*

## The convergence is calculated at vertical levels from the surface (10m wind), 1000, 925, 850, 700, 500 mb.  Thus, if the convergence criteria is 6 vertical levels (e.g., C1), then all the vertical levels must exceed the convergence amplitude criteria.

- Criteria	Convergence		Number of Vertical
- 		Amplitude (10-5s-1)		levels required to meet
- 					the criteria for severe weather
- C1			>  3.0			6 (<400 mb)
- C2			>  3.0			5 (<500 mb)
- C3			>  5.0			6 (<400 mb)
- C4			>  5.0			5 (<500 mb)
- C5			>10.0			6 (<400 mb)
- C6			>10.0			5 (<500 mb)
*For lifted index tests:*
- C7			< -3
- C8			< -4
- C9			< -5

## Excerpt showing convergence criteria and distance form the watch box in km. 0 km means the convergence criteria points were within the watch box (Hits). 

## Total number of hits or distance from the watch box for convergence exceeding the criteria for all watch boxes.  Same for Lifted index for C7 and C8 criteria. A six week period containing 47 watch boxes was used to gather the SPC Watch (no Warnings were issued in this period) box locations.

- 			Criteria
- (km)	C1	C2	C3	C4	C5	C6	C7	C8
- Hits	 0	27	 0	25	 0	13	17	 7
- <100	 4	 0	 3	 0	 2	 0 	 3	 3
- 100-200	 5	 0	 3	 0	 1	 0	 9	13
- 200-300	14	 0	11	 0	 7	 0	 6	  7
- >300	13	12	11	 6	13	 6	 6 	12
- N/A	11	 8	19	16	24	28	 6	  5

## Summary of Results

- The criteria C2, C4 were superior with the least distance errors compared to lifted index.
- Requiring the vertical extent of the convergence criteria to extend past 500 mb C1, C3, C5, does not improve the accuracy.
- We found the “Best” Lifted Index to have a larger number of false alarms and distance errors larger than 200 km.
- A six week period containing 47 watch boxes was used to gather the SPC Watch (no Warnings were issued in this period) box locations.
-  Model initial conditions were set as the nearest such that 24-h forecasts to the valid times covered by the Watch box could be made.
- NOMADS OPEN-DAP/DODS queries can be used to make client (user) calculations.

## Conclusion

- Model  predicted convergence patterns have signatures that indicate the potential of severe weather using the SPC Watch and Warning Box product as verification.
- The volume or shape as measured by vertical extent and amplitude of the convergence pattern was used to test the accuracy of predicting the potential for severe weather.
- Convergence amplitude and vertical extent appear to be competitive with other stability measures like “Best” Lifted Index.
- Forecasters viewing the 3-Dimensional convergence structures of model forecasted convergence patterns could potentially improve their severe weather predictions.
- NOMADS OPEN-DAP/DODS servers can enhance user access to NOAA model database.
- Quantitative verification statistics will be improved to include false alarm rates and threat scores when more samples are used.

## Real Time Vis5D files from NCEP Model Forecasts

- _[http://www.emc.ncep.noaa.gov/gmb/wd23ja/vis5d.html](http://www.emc.ncep.noaa.gov/gmb/wd23ja/vis5d.html)_
- _[http://www.emc.ncep.noaa.gov/gmb/wd23ja](http://www.emc.ncep.noaa.gov/gmb/wd23ja)_/vis5d/avn3h
- for the GFS over the CONUS
- Western and Northern hemisphere add /avn
- South America add /avnsa
- Africa add /gfsaf
- Improved vertical resolution over the CONUS add gfsv
- Eta #212 grid:  _[http://www.](http://www.emc.ncep.noaa.gov/gmb/wd23ja)__[emc](http://www.emc.ncep.noaa.gov/gmb/wd23ja)__[.](http://www.emc.ncep.noaa.gov/gmb/wd23ja)__[ncep](http://www.emc.ncep.noaa.gov/gmb/wd23ja)__[.](http://www.emc.ncep.noaa.gov/gmb/wd23ja)__[noaa](http://www.emc.ncep.noaa.gov/gmb/wd23ja)__[.](http://www.emc.ncep.noaa.gov/gmb/wd23ja)__[gov](http://www.emc.ncep.noaa.gov/gmb/wd23ja)__[/](http://www.emc.ncep.noaa.gov/gmb/wd23ja)__[gmb](http://www.emc.ncep.noaa.gov/gmb/wd23ja)__[/wd23ja](http://www.emc.ncep.noaa.gov/gmb/wd23ja)_/vis5d/eta212
- Global Ensembles stacked in the vertical dimension:
-  _[http://www.](http://www.emc.ncep.noaa.gov/gmb/wd23ja)__[emc](http://www.emc.ncep.noaa.gov/gmb/wd23ja)__[.](http://www.emc.ncep.noaa.gov/gmb/wd23ja)__[ncep](http://www.emc.ncep.noaa.gov/gmb/wd23ja)__[.](http://www.emc.ncep.noaa.gov/gmb/wd23ja)__[noaa](http://www.emc.ncep.noaa.gov/gmb/wd23ja)__[.](http://www.emc.ncep.noaa.gov/gmb/wd23ja)__[gov](http://www.emc.ncep.noaa.gov/gmb/wd23ja)__[/](http://www.emc.ncep.noaa.gov/gmb/wd23ja)__[gmb](http://www.emc.ncep.noaa.gov/gmb/wd23ja)__[/wd23ja](http://www.emc.ncep.noaa.gov/gmb/wd23ja)_/vis5d/ens
- RSM over Hawaii at 10 km: _[http://www.](http://www.emc.ncep.noaa.gov/gmb/wd23ja)__[emc](http://www.emc.ncep.noaa.gov/gmb/wd23ja)__[.](http://www.emc.ncep.noaa.gov/gmb/wd23ja)__[ncep](http://www.emc.ncep.noaa.gov/gmb/wd23ja)__[.](http://www.emc.ncep.noaa.gov/gmb/wd23ja)__[noaa](http://www.emc.ncep.noaa.gov/gmb/wd23ja)__[.](http://www.emc.ncep.noaa.gov/gmb/wd23ja)__[gov](http://www.emc.ncep.noaa.gov/gmb/wd23ja)__[/](http://www.emc.ncep.noaa.gov/gmb/wd23ja)__[gmb](http://www.emc.ncep.noaa.gov/gmb/wd23ja)__[/wd23ja](http://www.emc.ncep.noaa.gov/gmb/wd23ja)_/vis5d/rsmh10