The System for Convection Analysis
and Nowcasting (SCAN)
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0-3 Hour Rainfall and Lightning Forecasts
|Products:||CONUS:||NE US:||SE US:||NC US:||SC US:||NW US:||SW US:|
|Probability of rain > 0.1 inch||X,||X,||X,||X,||X,||X,||X,|
|Probability of rain > 0.5 inch||X,||X,||X,||X,||X,||X,||X,|
|Probability of rain > 1 inch||X,||X,||X,||X,||X,||X,||X,|
|Probability of rain > 2 inches||X,||X,||X,||X,||X,||X,||X,|
|Probability of CG lightning||X,||X,||X,||X,||X,||X,||X,|
Probability of local rainfall exceeding 0.1, 0.5, 1, and 2 inches;
"Best guess" rainfall amount;
Probability of 2 or more lightning strikes.
These products indicate probabilities of rainfall exceeding certain thresholds, a 'best estimate' peak rainfall amount, and probability of cloud-to-ground lightning. Rainfall forecasts are for the highest rainfall amounts within square regions 40 km (~20 miles) on a side. Lightning forecasts are for the probability of two or more strikes within the same regions.
Input to the products includes a national radar composite, infrared satellite imagery, cloud-to-ground lightning strike observations, and numerical weather prediction model forecasts. All data are input to an extrapolative/statistical algorithm that analyzes the intensity, position, and short-term movement of rainfall and convective systems, and general atmospheric conditions (humidity, stability, and vertical motion) conducive to rain.
At present the output takes the form of color-coded boxes on county-state map backgrounds. The box format accounts for the fact that the probability and rainfall amount forecasts refer to the maximum rainfall values over the entire box, not at individual points.
More complete documentation includes a full explanation of the model development and performance characteristics.
Interruptions will generally be corrected only during working hours between Monday and Friday.
Always rely on NOAA Weather Radio and the broadcast media for official forecasts and warnings.