RRFS Operationalization Postponed (Again)

The operational implementation of the Rapid Refresh Forecast System (RRFS) and RRFS Ensemble Forecast System (REFS) has been postponed again to November 3rd.  That operationalization also includes sunsetting several ancient NCEP forecast systems including the NAM, HREF, SREF, and HiresW.  Those modeling systems will live for a few more days.  

Per the NCEP Service Change Notice Update released on October 15, the delay is to include changes to precipitation type products produced during model postprocessing due to overforecasting of freezing rain and underforecasting of ice pellets.  These are issues that have been a thorn in my side for the HRRR and RRFS snow products for some time.  

In the case of overforecasting freezing rain, we've seen this frequently in the HRRR and the RRFS.  An example is below.  Apologies for the lack of a map, but the black circle is Alta and the area of pink , purple, and light blue around it denotes an area of forecast winter precipitation in the central Wasatch last weekend.  While snow is anticipated for some of the high elevation area, this RRFS member is also producing areas of snow mixed with freezing rain.  This happens frequently during lighter precipitation periods.


In the case of underforcasting ice pellets, the issue from my end is that NCEP does not distinguish between snow pellets (a.k.a. graupel) and ice pellets (a.k.a. sleet).  They are lumped together in the ice pellet category.  This is an issue for our snow-to-liquid ratio estimates because we would like to treat graupel and sleet separately.  

To deal with these issues, I've kludged together some approaches but problems remain.  The service change notice update suggests they are changing how they are calculating instantaneous precipitation type fields, which I used to determine precipitation type for our HRRR and RRFS products.  

I have not been able to locate a reference that describes what NCEP is now doing, so we will just have to see how things look when the RRFS starts producing precipitation again.  Hopefully it is a better product.  

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