Chinook Posted August 2, 2013 Share Posted August 2, 2013 I was looking at the number of hail and wind reports per year, as shown on the SPC web page: http://www.spc.noaa.gov/climo/online/monthly/newm.html I was trying to compare different annual severe thunderstorm trends. I came upon something interesting that I hadn't thought about before. The hail criterion change in 2010 greatly changed the number of hail reports going into the database. Year 2005: Hail 13640, Wind 12016. Hail and wind reports were about 12% different Year 2006: Hail 16566: Wind, 13669: Hail and wind reports were 17% different Year 2007: Hail and Wind were both around 12000. Hail and wind reports were within 2.2% of each other. Year 2008. Hail 17680, Wind: 16819. Hail and Wind reports were within 4.8% of each other Year 2009. Hail: 10223, Wind: 11408. Hail and Wind reports were within 10.3% of each other On January 5, 2010, the SPC changed the hail criterion from 0.75" to 1.0". Therefore all 0.75" and 0.88" hail reports after that date are not in the database. Year 2010 (after the hail criterion change): Hail was about 5900, Wind was about 14000. Wind reports were 2.38x the number of hail reports. Year 2011. Wind was about 18000, Hail was about 9000. Wind reports were 1.98x the number of hail reports. My conclusion: The hail report probability across the country decreased by a factor of about 2, due to the hail criterion change. Before 2010, there were about 12000-13000 hail reports and 12000-13000 wind reports per year. After 2010, there have been about 12000-13000 wind reports and 6000-6500 hail reports per year. This is my own ballpark estimate. (not an actual computation.) Of course, all of those 0.75" and 0.88" hailstones are still out there, they are not counted in this database. So it is really not a change in how the weather works. Link to comment Share on other sites More sharing options...
icebreaker5221 Posted August 2, 2013 Share Posted August 2, 2013 I was looking at the number of hail and wind reports per year, as shown on the SPC web page: http://www.spc.noaa.gov/climo/online/monthly/newm.html I was trying to compare different annual severe thunderstorm trends. I came upon something interesting that I hadn't thought about before. The hail criterion change in 2010 greatly changed the number of hail reports going into the database. Year 2005: Hail 13640, Wind 12016. Hail and wind reports were about 12% different Year 2006: Hail 16566: Wind, 13669: Hail and wind reports were 17% different Year 2007: Hail and Wind were both around 12000. Hail and wind reports were within 2.2% of each other. Year 2008. Hail 17680, Wind: 16819. Hail and Wind reports were within 4.8% of each other Year 2009. Hail: 10223, Wind: 11408. Hail and Wind reports were within 10.3% of each other On January 5, 2010, the SPC changed the hail criterion from 0.75" to 1.0". Therefore all 0.75" and 0.88" hail reports after that date are not in the database. Year 2010 (after the hail criterion change): Hail was about 5900, Wind was about 14000. Wind reports were 2.38x the number of wind reports. Year 2011. Wind was about 18000, Hail was about 9000. Wind reports were 1.98x the number of hail reports. My conclusion: The hail report probability across the country decreased by a factor of about 2, due to the hail criterion change. Before 2010, there were about 12000-13000 hail and wind reports per year. After 2010, there have been about 12000-13000 wind reports and 6000-6500 hail reports per year. This is my own ballpark estimate. (not an actual computation.) Of course, all of those 0.75" and 0.88" hailstones are still out there, they are not counted in this database. So it is really not a change in how the weather works. Wasn't that the whole point? They wanted to raise the criteria for a warning so there are less warnings issued for marginal hail storms, thereby both reducing the number of warnings issued as well as the number of storms verifying as severe. Also helps to reduce the 'cry wolf' syndrome where people only pay attention to tornado warnings because half of all severe thunderstorms aren't 'that bad'. Link to comment Share on other sites More sharing options...
Chinook Posted August 2, 2013 Author Share Posted August 2, 2013 Wasn't that the whole point? They wanted to raise the criteria for a warning so there are less warnings issued for marginal hail storms, thereby both reducing the number of warnings issued as well as the number of storms verifying as severe. Also helps to reduce the 'cry wolf' syndrome where people only pay attention to tornado warnings because half of all severe thunderstorms aren't 'that bad'. Maybe I could offer this. The outlooks and watches offer hail probabilities, such as 15% for an outlook. Perhaps there are too agressive, in a pure numbers standpoint, because they are still thinking in pre-2010 terms. Link to comment Share on other sites More sharing options...
icebreaker5221 Posted August 2, 2013 Share Posted August 2, 2013 Maybe I could offer this. The outlooks and watches offer hail probabilities, such as 15% for an outlook. Perhaps there are too agressive, in a pure numbers standpoint, because they are still thinking in pre-2010 terms. Well I agree that the hail probabilities should reflect the change, but how do you know that they haven't? Link to comment Share on other sites More sharing options...
Chinook Posted August 2, 2013 Author Share Posted August 2, 2013 Well I agree that the hail probabilities should reflect the change, but how do you know that they haven't? I don't know for sure. I don't know anybody there personally. I think they are a top notch organization, so they probably gave it some thought before 2010. I sometimes wonder if the SPC outlooks verify numbers-wise, as opposed to a subjective verification. I don't have any software to show numbers-wise verification. Link to comment Share on other sites More sharing options...
weatherwiz Posted August 5, 2013 Share Posted August 5, 2013 I guess when doing research we'll just have to keep in mind the criteria change and start creating different data sets. Very interesting post though! Awesome to see the numbers since the change. Link to comment Share on other sites More sharing options...
Ellinwood Posted August 5, 2013 Share Posted August 5, 2013 Not sure about Slight Risk days, but Patrick Marsh recently compiled all of the Moderate/High Risk days and noted on Twitter that changes in the definitions have made it harder to achieve them over the years. There may be similar trends for Slight Risk days, though it is a lot easier to verify a Slight Risk day, so the drop may not be as notable. Link to comment Share on other sites More sharing options...
nwohweather Posted August 6, 2013 Share Posted August 6, 2013 Well I think the major improvements in forecasting the last 10 years technologically speaking should have helped reduce the amount of big severe weather predictions as we are more accurate now. However I will say we are on a downtick the last two years as well, there have been a few major outbreaks that stand out, but it seems the last 3 years anyways have been extremely condensed activity wise Link to comment Share on other sites More sharing options...
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