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SPC SREF Overview

The SPC Short-Range Ensemble Forecast (SREF) is constructed by post-processing all 26 members of the NCEP SREF each 6 hours (03, 09, 15, and 21 UTC). Output is available at 3h intervals through 87 hours. The SPC ensemble post-processing focuses on diagnostics relevant to the prediction of SPC mission-critical high-impact, mesoscale weather including: thunderstorms and severe thunderstorms, large scale critical fire weather conditions, and mesoscale areas of hazardous winter weather. Presentation of the SREF output via this WEB portal is similar to its presentation at the SPC within the N-AWIPS operational display system. All SREF information presented herein is for guidance purposes only and remains under development. This ensemble guidance should not be mistaken for or used in lieu of operational SPC products and forecasts.

Each ensemble field or diagnostic is associated with a specific statistical attribute (e.g., the ensemble mean or exceedance probability). This statistical attribute is denoted by a coded prefix as described below.

  • [PR]: Probabilistic value. The probability may be an uncorrected exceedance probability, a "combined" or joint probability, or a post-processed calibrated probability. All post-processed calibrated probabilities are found under the menu heading "Post-Processed Guidance;" otherwise, the probabilistic values are unadjusted. Calibration involves additional post-processing of the SREF output in an effort to (1) remove the systematic bias of the model(s) and (2) improve the reliability and resolution of the probabilistic forecast. For information on the SREF calibrated thunderstorm or severe thunderstorm guidance see the following links.
    Calibrated thunderstorm guidance:
    Calibrated severe thunderstorm guidance:
  • [MAX]: The maximum value from any member at each grid point.
  • [MD]: The median value at each grid point.
  • [MDXN]: The median at each grid point (solid contours) along with the union (i.e., maximum in spatial extent) and the intersection (i.e., minimum in spatial extent) overlaid. The outer thick, dashed line is the union of all members at the first median contour value (i.e., where at least one of the 22 members exceeds the value of the first median contour). The inner thick, dashed line is the intersection of all the members at the first median contour value (i.e., where all 22 members intersect and exceed the value of the first median contour). This plot shows a measure of SREF central tendency using the median, and its spatial variability via the union and intersection of all the members.
  • [MIN]: The minimum value from any member at each grid point.
  • [MN]: The ensemble mean; i.e., the mean value at each grid point.
  • [MNSD]: The ensemble mean and standard deviation at each grid point.
  • [PM]: Probability Matched Mean (i.e., combination of PDFs)
  • [SP]: Spaghetti diagram.

    Thanks to Steve Listemaa and Steven Zubrick (WFO Sterling) for contributing the dSREF/dT hovering capability.

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