ThreadEx NOAA   NCDC   NWS  

Threaded Station Extremes

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Project Background

ThreadEx is a project designed to address the fragmentation of station information over time due to station relocations for the express purpose of calculating daily extremes of temperature and precipitation. There are often changes in the siting of instrumentation for any given National Weather Service/Weather Bureau location over the observational history in a given city/region. As a result, obtaining a long time series (i.e., one hundred years or more) for computation of extremes is difficult, unless records from the various locations are "threaded" or put together. This has been done, but different approaches and combinations of stations have resulted in confusion among data users and the general public about what constitutes an official daily extreme record.

In consultation with NOAA's National Climatic Data Center (NCDC) and the National Weather Service (NWS), the Northeast Regional Climate Center (NRCC) has evaluated station relocations and built "threads" for 268 locations that are published in NCDC's Local Climatological Data using NOAA daily data sets. The data sets used for this project included NCDC DSI3210, DSI3200, DSI3206 and DSI3205. In addition, NRCC was able to extend over sixty station threads back further in time using daily data contributed by local NWS offices, state climate offices and regional climate centers.

Methodology for Developing Threads

The record of a currently active station was used as the starting point for a station thread. This station's current record was used as far back in time as possible, taking precedence over a closed station's record during any periods of overlap. A search was conducted to identify other weather stations in the area that could be used to extend the thread further back in time. In this process, preference was given to Weather Service/Bureau stations (that were not themselves LCD stations). The thread was extended back in time as far as possible using NOAA daily data available in digital form. Partner input was solicited and this local expertise was used to fine-tune the station threads.


If you have any questions, contact Tim Owen at NCDC ( or Keith Eggleston at NRCC (

Version 1.0 - released 13-March-2006.
Revision History.