Verification of RUC-2 forecasts for NAOS

The North American Observing System (NAOS) is a cooperative program supported by governmental organizations and universities in Canada, Mexico, and the United States. Its purpose is to make recommendations on the configuration of the upper-air observing program. An integral part of NAOS is the Test and Evaluation Working Group whose task is to carry out hypothesis testing regarding possible changes to the current upper-air observing system. The first hypothesis states, “It will be possible to reduce the number of rawinsondes in the U.S. network without noticeably reducing forecast accuracy provided that the sites removed have substitute observing systems already in place.” For Hypothesis 1 testing, the Numerical weather Prediction (NWP) models are run with three different upper-air system configurations. The control run uses the observing system as currently configured. The second run excludes rawinsonde observations from 14 stations that are located near busy airports where commercial aircraft provide frequent soundings of temperature and winds on ascent and descent. In the third run, both the aircraft and radiosonde observations are excluded from the model at the same 14 locations. The period of time selected for Hypothesis 1 testing is 25 January through 25 February 1998.

This paper presents preliminary results from the Rapid Update Cycle (RUC) test for Hypothesis 1. The RUC is one of several numerical weather prediction models run at NCEP. Since the RUC provides frequently updated short-range (primarily 0-12 h) weather forecasts; it is an important part of the NAOS simulations in providing information about the effect, if any, on short-range numerical weather predictions (out to 36-h) when removing selected rawinsonde observations.