SFR performance at temperatures below 22 DegF

SFR_1605UTC_012614

On Jan 26 2014, an upper level shortwave caused an area of light snow across Ohio, western Pennsylvania and the northern counties of West Virginia. Surface temperatures were quite cold with readings generally in the teens. Even at these cold temperatures, the SFR product did indicate snowfall across the far northern counties of our forecast area.

The maximum snowfall rates indicated on the 1605 UTC product was about 0.3 to 0.4 inches per hour. Based on reports, these numbers appear to be representative of what actually was occurring.

While this is just one case, the SFR product appears to work reasonably well at temperatures below 22 DegF.

2 thoughts on “SFR performance at temperatures below 22 DegF

  1. Thanks for looking at the product even if the temperatures were below the threshold. This is very helpful information and valuable feedback!

    Huan, in some of the earlier cases we looked at, the product was “blacked out” when temperatures were below 24F. In this instance, though, SFR values were obtained even with temperatures below 20F. Can you shed some light on why that would be the case?

  2. The snowfall detection component of the SFR algorithm actually relies on satellite measurement rather than surface temperature to filter out cold conditions. The specific channel we use (53.6 GHz) is sensitive to the temperature in a thick layer of atmosphere from the surface to about 6-7 km. The peak of its weighting function is at 550 mb. We set a fixed threshold to this channel and don’t do retrieval if the measurement at this channel is below the threshold. The reason we use this frequency is that it gives better indication than surface temperature about if the condition is favorable for detecting snow signals. While 53.6 GHz has a fairly high correlation with surface temperature statistically (the basis of our statement that surface temperature needs to be 22°F or above), there is a wide scattering in how the two relate in individual cases. This event is a good example where the surface was cold while the atmosphere was relatively warm so the algorithm proceeded with the retrieval process.

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