# Presentation: 933709

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## Forecasts of Rainfall Amount and Lightning Occurrence From an

**Extrapolative-Statistical Technique**
**Utilizing Multiple Remote Sensor**
**Observations**

- David H. Kitzmiller
- Scott D. Vibert
- Fred G. Samplatsky
- Decision Assistance Branch
- Meteorological Development Laboratory
- NOAA National Weather Service

**October 2000**

***Update: July 2002***

## PURPOSE

- System for Convection Analysis and Nowcasting (SCAN)

- Automated monitoring of radar, satellite, and lightning observations, and numerical model output, in terms of the short-term threat for rainfall and lightning
- Yields forecasts of rainfall probability, rain amount, lightning probability
- Directs forecasters' attention to regions of the greatest threat for heavy rainfall and lightning

## Today=s topics

- Development principles
- Sample output
- Performance characteristics
- Accessing real-time output

## Thanks to:

- Robert Saffle, Robert Elvander
- Bryon Lawrence, Jeff Ator
- Mark Lilly
- Sun Junyuan
- Chaka Ruffin
- Office of Hydrology
- Global Hydrology Research Center

## Input

- 10-km, 7-level national radar mosaic from Radar Coded Messages
- 10-km GOES temperature field (11-F)
- CG lightning strike field: 15-minute strike count within 10-km grid boxes
- NWP output: RH, stability indices, precip, wind vectors.
- Used NGM archive for development; can use NGM or Eta operationally

## Output Products

- Probability of rainfall exceeding 0.1, 0.5, 1, and 2 inches
- Peak rainfall category
- Probability of two or more CG lightning strikes
- Forecasts are for highest amount in grid boxes   40 km on a side
- Valid period 00:30 to 3:30 after radar obs

## Basic Principles I

- Based on extrapolative-statistical technique
- Initial-time radar reflectivity, satellite temperature, and CG lightning strike rate fields are extrapolated for 3 h with 700-500 mb winds
- Statistical predictors are derived from initial-time and extrapolated fields, NWP output
- Process repeated for many historical cases in which subsequent rainfall and lightning observations exist

## Basic Principles II

- Statistical regression was used to find optimum combinations of variables for predicting occurrence of rainfall and lightning events
- Equations were developed from ~400 warm-season and ~300 cool-season cases, 1996-1999
- Equations with only satellite/NGM/lightning predictors supply probabilities in radar gaps
- For warm season developed equations for 8 periods of the day
- Stage III estimates served as rainfall "ground truth"
- Used GAI lightning observations

## Basic Principles III

- Multiple equations derived: All predictors, initial- time only, no-radar
- Equations with limited predictor sets supply probabilities in and downstream of radar data voids
- Categorical rainfall amount forecasts derived by applying thresholds to probabilities

## Reflectivity at 2030 UTC, 2 May 1997

**Reflectivity at 2030 UTC, 2 May 1997**

## GOES-8 11-F temperature, 2015 UTC 2 May 1997

**GOES-8 11-****F**** temperature, 2015 UTC 2 May 1997**

- Cyan: -10EC; Green: -30EC; Red: -50EC

## Boxes with CG lightning, 2010-2025 UTC, 2 May 1997

**Boxes with CG lightning, 2010-2025 UTC, 2 May 1997**

## Maximum Reflectivity Forecast 2100-0000 UTC, 2-3 May 1997

## Forecasted GOES-8 temperature, 2100-0000 UTC

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## Verifying 3-h rainfall observations, Stage III analyses

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## Candidate Predictors

- Radar: Maximum reflectivity; rainfall forecast; areal coverage of 40+ dBZ echoes
- Satellite: Minimum temperature forecast; T700-Tsat
- Lightning: Initial-time and maximum forecasted 15-minute strike rate
- NGM: K index, RH, PW, LI, moisture divg, 6-h rainfall amount

## CORRELATION RATIOS: 0.1"

- Radar-satellite-lightning-model predictors
- 2100-0000 UTC valid period- warm season

## Probability of 0.1"+, 2100-0000 UTC

- P(0.1) = -0.869
-             + 0.491 RADSAT0.1
-         {Radar reflectivity/Tsat probability table}
-             + 4.512 Max REFL (0-3h)
-         {Radar reflectivity extrapolation forecast}
-             + 3.510 MXREF3x3 (initial-time)
-         {Max initial-time radar reflectivity}