SFR performance during transition from rain to wintry precipitation.

SFR_0220UTC_02162016

During the afternoon and early evening hours on 2/15/2016, a large area of rain covered much of northeast Kentucky and southeast Ohio as well as the western half of West Virginia.

An upper level disturbance then moved across the area during the evening and overnight hours with the rainfall mixing with and then transitioning to all snow.

I wanted to show how the SFR image performed during this transition.  The image above is from 0220 UTC on 2/16/2016.  At that time, much of the precipitation across West Virginia was still in the form of rain…with an area of snow extending from northwest Pennsylvania across central Ohio into southwest portions of that state.

There appears to be several observations of rain across Ohio with surface temperatures  of 32 to 35 DegF  where the SFR product indicated snow in the clouds.  It does appear that where surface temperatures were warmer than 35 DegF, the SFR product did not indicate any snow in the clouds.

From an earlier post, I believe the SFR throws out snow when the model-based 10-m temperatures exceeded 33 DegF.  Is this filter working in this situation?

 

4 thoughts on “SFR performance during transition from rain to wintry precipitation.

  1. I received some additional information on different thresholds that we use to determine weather in our CWA. I figured that putting the information here may lead to additional discussion from other offices.

    If the 850mb temperatures are at least -6 DegC, we can have snow with a surface temperature as high as 34 or 35 DegF. If the surface temperature is 35 DegF, it could be a mix of rain and snow.

    If the 850mb temperatures are at lease -10 DegC, we can have snow with a surface temperature as high as 36 or 37 DegF. If the surface temperature is 37 DegF, it could be a mix of rain and snow.

    I have seen mostly snow with a surface temperature as high as 38 DegF when our 850mb temperature was colder than -12 DegC.

    One of our forecasters also informed me that we generally need a 925mb temperature of -2 DegC or colder for snow. However, this is not applicable across some of our CWA as that level would be located underground.

    Does anyone else have any thoughts?

    • Thanks a lot for the info on the correlation between 850mb temperature and surface precipitation phase. We’ll look into how to adjust our snowfall detection algorithm based on this knowledge.

      • I have asked a few other offices for guidance on the thresholds that they use. If I hear back from them, I will forward their information to you as well.

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