According to the treatises writen by David, Shunman and Sullivan, routine operation, verification procedures and evaluation of 33 years of Quantitative Precipitation Forecasting at the NMC U.S.A were reviewed.
Verification graphs show steady improvements in forecast accuracy,especially for the longerrange forecasts, which in this context are those in the 24 — 60h range. During the 1960s the Threat Score (TS) for day-2 forecasts for 1 inch or more of precipitation was averaged approximately 0. 07. During recent years,that score has nearly doubled,and the 36 —60h period forecast in 1993 had a TS comparable to that for the 12 —36h period during the 1960s.