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This blog helps to explain why the National Weather Service changed their predictions from 2-4", to 6-8" to 12-18" and finally to 24+".
http://4029weather.wordpress.com/2011/02/10/historic-snowstorm-becomes-more-puzziling/
Historic Snowstorm Becomes More Puzzling
(Image on our Super Doppler Radar around 8am February 9, 2011)
This winter has been one for the ages, especially the past 48 hours. Northwest Arkansas has topped the 24 hour snowfall record, the single storm snowfall record, and the seasonal snowfall record for at least the last 70 years. In northern Benton and Carroll County the snowstorm of March 10-12, 1968 and the 1967-68 seasonal snow totals still rival this storm and there were a couple other years in the 1910s that we believe may compare as well. Otherwise, this one takes the cake. To top it off, low temperatures just shattered all-time records a day after the storm. Whether you love or hate winter, you have to behold the once in a lifetime events for our area.
The puzzling part is trying to piece together exactly why this historic snowstorm came to fruition. As most of you know the computer models did a terrible job with the storm. Some have made note of how the NAM was the closest, which is true. On the other hand, it still missed the mesoband of snow which dropped almost all of the snowfall in northwest Arkansas. To top it all off, we all assumed that the snow was just an extremely dry or “fluffy snow” where the snow ratios were 20 to 1 or higher (meaning 1 inch of rain or liquid would equal 20″ or more of snowfall). We are now finding out that wasn’t the case. While the snow wasn’t heavy it also wasn’t as light as we thought. At my house in Springdale, I measured 20″ of snowfall, yet 3 core samples of the snow showed 1.6″ of liquid on average in the snowfall (this does not include moisture from previous snow on the ground before Tuesday). A similar measurement at our station in Rogers showed that 17″ of snowfall led to 1.55″ of liquid. This gives us a snowfall ratio between 11 to 13 to 1, which is a far cry from the expected findings. These ratios were also found at other ASOS and CoCoRaHS sites as well. While some of the observations did show higher ratios, it is still lower than expected.
So what is the big deal?
Lower ratios mean that there is a lot more moisture in the snow…moisture that wasn’t forecast by computer models. For example, about 4 to 8 times more moisture fell from the sky than what the GFS had forecasted and about 3 times more moisture fell compared to the Tuesday 00z (Monday 6pm) NAM. Literally the computer models, our lifeline for forecasting the weather beyond 24 hours, failed. This event is a unprecidented event in many ways for northwest Arkansas and now it may be the focus on future research projects as well. The reason the snow fell so hard for so long was rather simple. An extremely intense mesoband of snow lined up along highway 412 and didn’t budge for over 6 hours. What isn’t simple is understanding why the mesoband formed and more importantly why it stayed locked into place while weather all around it moved fluidly. There are things that we still don’t understand, and this is a great example of it. I am very interested to see further reasearch done on this storm, and more importantly the forecasting lessons we can take away from it. Yesterday, was one of the most humbling and surreal days of my life. One of you on here asked, if this event is a Meteorologist’s dream or nightmare…and the answer is both! While we never want to provide an inaccurate forecast, it the by far the most intense snowstorm I have ever witnessed despite living through blizzards in the Midwest and mountain snows in West Virginia. It was a delight to watch and now it will be interesting to understand the mystery behind one of Arkansas’s biggest snowstorms ever.
Ross Ellet
http://4029weather.wordpress.com/2011/02/10/historic-snowstorm-becomes-more-puzziling/
Historic Snowstorm Becomes More Puzzling
(Image on our Super Doppler Radar around 8am February 9, 2011)
This winter has been one for the ages, especially the past 48 hours. Northwest Arkansas has topped the 24 hour snowfall record, the single storm snowfall record, and the seasonal snowfall record for at least the last 70 years. In northern Benton and Carroll County the snowstorm of March 10-12, 1968 and the 1967-68 seasonal snow totals still rival this storm and there were a couple other years in the 1910s that we believe may compare as well. Otherwise, this one takes the cake. To top it off, low temperatures just shattered all-time records a day after the storm. Whether you love or hate winter, you have to behold the once in a lifetime events for our area.
The puzzling part is trying to piece together exactly why this historic snowstorm came to fruition. As most of you know the computer models did a terrible job with the storm. Some have made note of how the NAM was the closest, which is true. On the other hand, it still missed the mesoband of snow which dropped almost all of the snowfall in northwest Arkansas. To top it all off, we all assumed that the snow was just an extremely dry or “fluffy snow” where the snow ratios were 20 to 1 or higher (meaning 1 inch of rain or liquid would equal 20″ or more of snowfall). We are now finding out that wasn’t the case. While the snow wasn’t heavy it also wasn’t as light as we thought. At my house in Springdale, I measured 20″ of snowfall, yet 3 core samples of the snow showed 1.6″ of liquid on average in the snowfall (this does not include moisture from previous snow on the ground before Tuesday). A similar measurement at our station in Rogers showed that 17″ of snowfall led to 1.55″ of liquid. This gives us a snowfall ratio between 11 to 13 to 1, which is a far cry from the expected findings. These ratios were also found at other ASOS and CoCoRaHS sites as well. While some of the observations did show higher ratios, it is still lower than expected.
So what is the big deal?
Lower ratios mean that there is a lot more moisture in the snow…moisture that wasn’t forecast by computer models. For example, about 4 to 8 times more moisture fell from the sky than what the GFS had forecasted and about 3 times more moisture fell compared to the Tuesday 00z (Monday 6pm) NAM. Literally the computer models, our lifeline for forecasting the weather beyond 24 hours, failed. This event is a unprecidented event in many ways for northwest Arkansas and now it may be the focus on future research projects as well. The reason the snow fell so hard for so long was rather simple. An extremely intense mesoband of snow lined up along highway 412 and didn’t budge for over 6 hours. What isn’t simple is understanding why the mesoband formed and more importantly why it stayed locked into place while weather all around it moved fluidly. There are things that we still don’t understand, and this is a great example of it. I am very interested to see further reasearch done on this storm, and more importantly the forecasting lessons we can take away from it. Yesterday, was one of the most humbling and surreal days of my life. One of you on here asked, if this event is a Meteorologist’s dream or nightmare…and the answer is both! While we never want to provide an inaccurate forecast, it the by far the most intense snowstorm I have ever witnessed despite living through blizzards in the Midwest and mountain snows in West Virginia. It was a delight to watch and now it will be interesting to understand the mystery behind one of Arkansas’s biggest snowstorms ever.
Ross Ellet
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