This document, written by Captain Frederick G. Meyer, Valery J. Dagostaro, and Major David T. Miller, describes the visibility and obstruction to vision forecasts produced operationally since July 1993 by the Techniques Development Laboratory (TDL) of the National Weather Service (NWS). TDL has derived regression equations to predict the probabilities of five categories of visibility and three categories of obstruction to vision. The equations were developed by applying the Model Output Statistics (MOS) technique to output from the Nested Grid Model (NGM).

In addition to the probability forecasts, categorical
forecasts are produced by a selection scheme designed to maximize the threat
score while retaining a bias value near 1.0. NGM MOS visibility and obstruction
to vision forecasts are produced for projections from 6 to 36 hours at 3-h intervals
and for projections from 42 to 60 hours at 6-h intervals after 0000 and 1200
UTC. The 54- and 60-h forecasts are disseminated only to stations supported
by the United States Air Force (USAF).

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Last Modified: November 03, 1997