Thunder Road Posted August 28, 2011 Share Posted August 28, 2011 I'm familiar with using BV and SRV scans to find areas of rotation in classic tornadic thunderstorms. But in a landfalling TC where the storms are much lower-topped and the winds are for the most part unidirectional, how does one detect tornadic rotation on radar? Last night when I saw all those TORs pop up, I didn't see anything on TPHL's BV scan (KDIX was not updating at the time) and I couldn't get TPHL's SRV scan to produce anything. And I figured KDOX was too far away to see a tor in Bucks County. So....how? Link to comment Share on other sites More sharing options...
Fred Gossage Posted August 28, 2011 Share Posted August 28, 2011 If you were using Level 3 NEXRAD data, you very likely would've had a really tough time detecting any rotations because of the resolution of the data, compared to how small the circulations are. If you were using Level 2 data, it could've been a case where the circulations were weak but got warnings anyway... or that the circulations were still very small and not easily detected, and the warning forecasters used other clues... such as weak circulations co-located with a reflectivity notch and high spectrum width... or a "one-sided couplet"... where you have very strong winds either inbound or outbound... right next to winds that are next to nothing (a bright red pixel, next to a gray one.... or a bright green one, next to a gray one).... and co-located with a reflectivity notch or something. The circulations inside these low-topped, mini supercells are often very hard to detect, and often.... if you end up with the same kind of significant gate-to-gate couplet that you would warn-on in the spring.... you have a significant tornado down doing damage in these setups. Edit: If you were using TDWR data.... you didn't have SRV available to you. This makes a world of difference, especially in fast-moving storms.... because a fast storm motion can often mask a circulation's true characteristics in the velocity data, and this is why storm-relative velocity exists. Link to comment Share on other sites More sharing options...
Thunder Road Posted August 28, 2011 Author Share Posted August 28, 2011 If you were using Level 3 NEXRAD data, you very likely would've had a really tough time detecting any rotations because of the resolution of the data, compared to how small the circulations are. If you were using Level 2 data, it could've been a case where the circulations were weak but got warnings anyway... or that the circulations were still very small and not easily detected, and the warning forecasters used other clues... such as weak circulations co-located with a reflectivity notch and high spectrum width... or a "one-sided couplet"... where you have very strong winds either inbound or outbound... right next to winds that are next to nothing (a bright red pixel, next to a gray one.... or a bright green one, next to a gray one).... and co-located with a reflectivity notch or something. The circulations inside these low-topped, mini supercells are often very hard to detect, and often.... if you end up with the same kind of significant gate-to-gate couplet that you would warn-on in the spring.... you have a significant tornado down doing damage in these setups. Edit: If you were using TDWR data.... you didn't have SRV available to you. This makes a world of difference, especially in fast-moving storms.... because a fast storm motion can often mask a circulation's true characteristics in the velocity data, and this is why storm-relative velocity exists. Oh okay thanks. I know the Lewes, DE one I could actually see a swirl on reflectivity but on the others not so much. So level 2 data is better? Link to comment Share on other sites More sharing options...
Fred Gossage Posted August 28, 2011 Share Posted August 28, 2011 Oh okay thanks. I know the Lewes, DE one I could actually see a swirl on reflectivity but on the others not so much. So level 2 data is better? Level 2 data is of higher resolution. If you are viewing the data within GR2Analyst (not sure about StormLab), you can give it a custom storm motion that turns base velocity into storm-relative velocity. If you have access to it, always always always go for storm relative velocity when trying to assess rotation within a thunderstorm... especially in faster storm motions. Link to comment Share on other sites More sharing options...
Thunder Road Posted August 28, 2011 Author Share Posted August 28, 2011 Level 2 data is of higher resolution. If you are viewing the data within GR2Analyst (not sure about StormLab), you can give it a custom storm motion that turns base velocity into storm-relative velocity. If you have access to it, always always always go for storm relative velocity when trying to assess rotation within a thunderstorm... especially in faster storm motions. I have GR3 now. I think I may ask Santee Clause for GR2AE Link to comment Share on other sites More sharing options...
Scotty Lightning Posted August 30, 2011 Share Posted August 30, 2011 I wondered this weekend since DIX was down and had to rely on DOX and OKX instead, what is the criteria for issuing a warning there? I know that radar returns could be false when on the outskirts of the radars normal range. All weekend I had GR2AE open for DOX and OKX, and then GRLevel 3 for PHL and EWR dopplers. I do remember that one cell in Wall/Brick that was not warned was showing a strong velocity return and I did see a path of twisted trees along the Parkway(near the cell phone towers/reservoir on the border of Wall and Brick...mile marker 94?) on my way home from being in NYC all weekend. Jim(BigJimsVideos) mentioned it on his FB page when reporting from Point Pleasant that he saw a funnel cloud/tornado. Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.