Where is the warm air?

The NWS, WNKY, and WBKO all mention that any snow that falls Thursday will mix with and possibly change over to rain during the afternoon. One reason they may be concerned about this is that as I mentioned in a previous post, there has been a model bias this winter that has often overestimated how much cold air will be present during all of the “near-miss” snow events we have had. To me, this appears to be a form of logical fallacy known as “proof by example”.

The idea goes like this…everytime we have had a storm with the potential to produce snow here in south-central KY, the computer models overestimated the available cold air, the storm turned out warmer than expected, and we received mainly rain. So now that we have another storm with the potential of snow, it appears the local forecasters are using this reasoning to suggest that the snow will change over to rain.

The reason that the models were incorrect in the previous storms was explained in my model bias post. And as I mentioned in that post, the reason for the model bias, the strong southeast ridge, is not evident in the atmosphere nor do the climate teleconnections support its existence. There are also other factors that lead me to believe that this will be mainly an all-snow event.

This is the first true arctic air mass that has been in place prior to a potential snow storm. Computer models have a hard time understanding the thermal structure of arctic air masses, since the represent an extreme condition in the atmosphere. This was discussed as model bias #2 in the previous post. Today’s forecast busts for maximum temperature for Bowling Green supports this idea. WNKY had a high of 35 and the NWS and WBKO had a high of 33 for BGKY today. The temperature at 2:00 pm was only 29, which represents an incorrect forecast of 4-6 degrees. Even if we assume the today’s high will be a degree or two higher, most forecasters were too warm with today’s forecast. Therefore, this time around, the computer models are actually underestimating, not overestimating, the amount of cold air in place.

If that weren’t enough, why not simply look at the models to see if they suggest a thermal profile that would support a changeover to rain Thursday afternoon. After all, with the previous storms, the computer models all caught on to the warming idea and showed both the 540 dm thickness line and the 0 degrees C 850 mb line well to the north of BGKY, which does support rain. For this storm, both the GFS, the NAM, NGM, all suggest than the storm is likely to remain all snow. Even the SREF composite forecasts of the location of the 540 and 0C lines show that the models are actually trending colder as the storm approaches.

So while I am not ruling out (nor are the models) the possibility that there might be a brief period of sleet or rain Thursday afternoon, I do expect this to be mainly a snow event for south-central KY. Still only 1-2 inches of snow, but it will be our first “plowable” snow of the year. The bad news is that the snow will become messy on the roads since there won’t be any melting since temperatures will stay below freezing for at least the next week.

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