The Hydro-Nowcaster: Recent Improvements and Future Plans Robert J. Kuligowski Roderick A. Scofield NOAA/NESDIS Office of Research and Applications Camp Springs, MD USA Clay Davenport I.M. Systems Group WWRP Symposium on Nowcasting and Very Short Range Forecasting 8 September 2005

The Hydro-Nowcaster: Introduction The Hydro-Nowcaster (HN) is an algorithm for producing 0-3 h nowcasts of precipitation based on extrapolated satellite estimates of rainfall rate. The Hydro-Nowcaster (HN) is an algorithm for producing 0-3 h nowcasts of precipitation based on extrapolated satellite estimates of rainfall rate. Both advection and growth/decay are considered. Both advection and growth/decay are considered.

The Hydro-Estimator (HE): Basis for the Nowcaster The HE is NESDIS’ operational infrared satellite rainfall algorithm The HE is NESDIS’ operational infrared satellite rainfall algorithm Rainfall areas are discriminated according to the value of pixel T relative to nearby values: Rainfall areas are discriminated according to the value of pixel T relative to nearby values: –Colder than average: active rain area –Warmer than average: inactive cold cloud

HE continued: Rain Rates Rainfall rates are based on pixel T, its value relative to surroundings, and moisture availability (precipitable water) Rainfall rates are based on pixel T, its value relative to surroundings, and moisture availability (precipitable water) Corrections are made for subcloud RH, orography, and convective EL (warm clouds) Corrections are made for subcloud RH, orography, and convective EL (warm clouds)

How the Nowcaster Works— Extrapolation Identifies clusters (regions bounded by fixed brightness temperature values) on two consecutive IR images Identifies clusters (regions bounded by fixed brightness temperature values) on two consecutive IR images Determines cluster motions based on the shift of the coldest 25% of pixels within a 100x100- pixel area that produces the best correlation between the two images Determines cluster motions based on the shift of the coldest 25% of pixels within a 100x100- pixel area that produces the best correlation between the two images Cloud motions are extrapolated out to 3 h at 15-min intervals based on the resulting motion vectors Cloud motions are extrapolated out to 3 h at 15-min intervals based on the resulting motion vectors

How the Nowcaster Works— Growth/Decay Each cluster on the current image is matched with one on the previous image according to the computed motion vector Each cluster on the current image is matched with one on the previous image according to the computed motion vector Three factors to determine growth/decay: Three factors to determine growth/decay: –Change in size of the cluster –Change in temperature of the coldest pixel –Change in mean temperature of the cluster The growth/decay factor linearly decays to zero over the 3-h forecast period to avoid unrealistic results The growth/decay factor linearly decays to zero over the 3-h forecast period to avoid unrealistic results

Example: Hurricane Katrina on 29 August h nowcast: 1200–1300 UTC 3-h nowcast: 1200–1500 UTC

Ongoing Work Recalibration of the HE to improve performance, particularly underestimation of rainfall associated with warm clouds Recalibration of the HE to improve performance, particularly underestimation of rainfall associated with warm clouds Rain/no rain discrimination is largely complete; recalibration of rain rate relationships is ongoing Rain/no rain discrimination is largely complete; recalibration of rain rate relationships is ongoing

Example: Mid-Atlantic Cold Front on 4-5 September h nowcast: 2100–2300 UTC (4) 3-h nowcast: 2100 UTC – 0000 UTC (5)

Where to Get the Data Nowcasts for 1, 2, and 3 h are updated every 15 minutes for the entire CONUS on the NESDIS Flash Flood Web page:

Future Work Complete recalibration of the HE, since the Nowcaster performance is highly dependent on its accuracy Complete recalibration of the HE, since the Nowcaster performance is highly dependent on its accuracy Improve the scheme for depicting cloud growth and decay—currently empirical Improve the scheme for depicting cloud growth and decay—currently empirical Develop an advection scheme for circular storms—motion vectors for multiple lags? Develop an advection scheme for circular storms—motion vectors for multiple lags? Account for the effects of orography on nowcasts of rainfall Account for the effects of orography on nowcasts of rainfall

Additional Plans Beginning collaboration between City College of New York, NOAA/National Weather Service, and NESDIS to evaluate and test multiple nowcasting frameworks (HN, TITAN, RDT) over the New York City metropolitan area. Beginning collaboration between City College of New York, NOAA/National Weather Service, and NESDIS to evaluate and test multiple nowcasting frameworks (HN, TITAN, RDT) over the New York City metropolitan area. Focus is on NYC, but results will be considered in operational nowcasting development in the US. Focus is on NYC, but results will be considered in operational nowcasting development in the US.

Questions?