Short-Range Ensemble Forecast (SREF) Derived Winter Weather Impact Graphics

This page displays automated SREF-derived probability graphics for winter weather event attributes considered significant to the public.  They are designed to address the aspects of winter weather events beyond accumulation - specifically duration, timing, and intensity.  Additional probability graphics provided are directed at assisting a NWS forecaster during the winter weather forecast process.

Please note the following:

Viewing the forecast graphics

Please use the menu on the right-hand side of this page to begin viewing the graphics. Clicking on any button will automatically remove the text in this window and replace it with a single graphic or forecast loop.
The following are set as defaults initially:
Note that if you wish to view the default options, simply click on one of the already selected buttons.

Once a single graphic or loop is loaded:

Product Description

NOTE - In each SREF member, the precipitation type (snow, sleet, freezing rain, or rain) is determined by taking the "dominant" type from five precipitation type algorithms: NCEP Baldwin/Schichtel, Revised NCEP, Ramer, Bourgouin, and Explicit Microphysics. The precipitation type used in the creation of these graphics is is determined by counting the dominant precipitation types from all 21 members, and the precipitation type with the highest count is taken as the SREF mean precipitation type for that time period.

INTENSITYIntensity is provided via two parameters - visibility (probability that the surface visibility is 1/2, 1/4, or 1/8 of a mile or less in winter precipitation) and precipitation rate (probability the winter precipitation rate is at least 1, 2 or 3" per hour).  Because the SREF output has a 3-hour temporal resolution,  the precipitiation rate is calculated by the 3-hour accumulated precipitation divided by 3 hours.  Both visibility and precipitation rate are calculated only where winter precipitation (Snow (S), Freezing Rain (ZR), or Ice Pellets or Sleet (IP)) is detected. 

DURATION:  The duration of a winter precipitation event (probability an event will last at least 12, 24, or 48 hours).  If a break in winter precipitation exceeds 12 hours, the "duration" clock is reset to zero at that forecast hour.

TIMING: All products are provided as loops to help discern timing of event attributes.