Monday, February 3, 2014

Got Snow??? ...Winter Weather Bust

Many are waking up this morning expecting to look outside and see a winter wonder land. However, most are only waking up to some very minor sleet and snow accumulations. In general, there were not even any reports of up to an inch of accumulation. Thus, in our books this was admittedly a "busted" forecast on our part. Our forecast of 3-6 inches posted yesterday afternoon is not exactly the 0.1" we officially received. In other words, our forecast was as bad as having to sit through a Super Bowl in which the Broncos got routed 43-8 to Seahawks last night. We know there are questions as to what went wrong and we want to be open in not shying away from an error in the forecast. We also want to explain a little about why things didn't favor the snow in the end.
A picture of the dusting of sleet and snow in Bowling Green courtesy of @Wx_Or_Not. Certainly far from the significant snowfall which was forecast.
To open, this has always been an extremely difficult forecast. If you are a frequent reader of the blog you should have gotten that impression as we tried to emphasize the difficulty in forecasting this system in prior posts. We knew all along that Warren County/Bowling Green was right on the line. In the end, we provided our best forecast based on the data we had, given the high amount of uncertainty. Here are a few quotes from our posts outlining the uncertainly:

"Totals are tough to judge. What we know as of now, a heavy snow band with a tight gradient will set up tonight in Kentucky. Current data suggests Bowing Green will be on the tip of this heavy snow line." - Posted Sunday at 4:18 pm

"The dividing line will be very close to our area and if the temperatures in the atmosphere can cool off just enough early on, a transition to snow will occur earlier. If it can't though, it may be that areas just to our north are seeing snow while our area hangs on to rain for several more hours. Truly just a tough call." -Posted Saturday at 10:02 pm

Seems like the second quote ended up being exactly what occurred as we saw rain while areas just to our north saw winter weather (mostly sleet at first) as early as mid afternoon yesterday. In the end, an area of snow did occur, but we ended up being just outside of the area that received the snow. For the most part that band was concentrated along the Western Kentucky Parkway corridor and east into central Kentucky. Below is a rough estimate of the snowfall totals from the NWS in Louisville.

So here is the what did/didn't happen... keep in mind that a technical question requires a technical response, but I'll try to keep it simplistic. To best sum it up, we had an area of warm air above the surface which was just above freezing. This resulted in what started falling as snow way up in the atmosphere, to melt and fall to the ground as rain. Once temperatures dipped below freezing, this became areas of freezing rain as it froze on contact. Eventually, when the area of warm air became smaller so to speak, the precipitation fell as some sleet. The graphic below explains the difference between why we may see snow, sleet, freezing rain, and rain. The graphic is courtesy of the NWS.

While we knew some sleet and freezing rain was possible, we expected that warm area of air to cool faster than it did, thus giving an area snow and heavy snow at that. Below is a model interpretation from the SREF model indicating this area of warm air. Notice how close the temperature (the red line) is to the blue freezing line... just a minor shift in this line and we see a significant snowfall in our area.

This SREF model data of the temperature profile from the surface to the upper atmosphere shows an area of warm air above freezing which caused the falling snowflakes to melt. Just a slight decrease in these temperatures would have resulted in much more snow.
Finally, just to provide an example of some of the behind the scenes data that we analyze... the image below is a short range model (HRRR) that was put out Sunday afternoon indicating 12 inches of snow in our area. While we were not crazy enough to believe those numbers, it just goes to show you how difficult it can be to try to make the right forecast given the data that we have. This was certainly not the only model indicating a significant snowfall.

We hope this gives you some insight into the forecast difficulty with a system like last night's. In the end, we hope to learn from this system and have an improved forecast in the future as a result. We also apologize if our bad forecast resulted in taking unnecessary action; but always better to be over prepared than under prepared. Also note that the snow/sleet/freezing rain did result is some slick spots on roadways, so be careful if traveling this morning. Thanks all for your support and thank you for reading. 

Forecaster: Ryan Difani

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