Mike Krzywonski
I often see tornado warnings which are issued based on what has been detected by doppler radar. Yet, when I click on the SRV1 tab on GRL3, I find that many times these cells don't even show a velocity couplet. What am I overlooking?
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After witnessing the continued decrease of involvement in the SpotterNetwork staff in serving SN members with troubleshooting issues recently, I have unilaterally decided to terminate the relationship between SpotterNetwork's support and Stormtrack. I have witnessed multiple users unable to receive support weeks after initiating help threads on the forum. I find this lack of response from SpotterNetwork officials disappointing and a failure to hold up their end of the agreement that was made years ago, before I took over management of this site. In my opinion, having Stormtrack users sit and wait for so long to receive help on SpotterNetwork issues on the Stormtrack forums reflects poorly not only on SpotterNetwork, but on Stormtrack and (by association) me as well. Since the issue has not been satisfactorily addressed, I no longer wish for the Stormtrack forum to be associated with SpotterNetwork.
I apologize to those who continue to have issues with the service and continue to see their issues left unaddressed. Please understand that the connection between ST and SN was put in place long before I had any say over it. But now that I am the "captain of this ship," it is within my right (nay, duty) to make adjustments as I see necessary. Ending this relationship is such an adjustment.
For those who continue to need help, I recommend navigating a web browswer to SpotterNetwork's About page, and seeking the individuals listed on that page for all further inquiries about SpotterNetwork.
From this moment forward, the SpotterNetwork sub-forum has been hidden/deleted and there will be no assurance that any SpotterNetwork issues brought up in any of Stormtrack's other sub-forums will be addressed. Do not rely on Stormtrack for help with SpotterNetwork issues.
Sincerely, Jeff D.
Greg Blumberg
EF4
Sometimes tornado warnings are issued based on Level 2 data instead of Level 3. Level 2 data has a much higher resolution and is the primary base radar data that is used by the NWS to make decisions. Most of the time Level 2 data resolution will pick up couplets and velocities better than Level 3 and they will base their decisions on that. One example I can think of was last Sunday with the storms near Roll, OK. We were running both GRLevel3 and GRLevel2 and Level 2 data showed the couplet, whereas Level 3 had trouble detecting it.
Also the warning decisions are very dependent on whether or not it's night time or day time.
Also the warning decisions are very dependent on whether or not it's night time or day time.
Jeff Snyder
EF5
As Greg noted, there is a significant difference between Level II and Level III radar data when it comes to the velocity products -- that's always been one of the biggest benefits of Level 2 radar data. Now, with super-res, even reflectivity differences between L2 and L3 data are rather significant. Not only does L2 reflectivity data have greater "intensity" resolution (much better than the 5 dBZ precision of Level 3 data), but L2 reflecitivty data now have much greater spatial resolution. At any rate, couplets are often much easier to see in Level II velocity data than the lower-resolution Level III velocity data.
Greg hinted at it with his last sentence -- there's more than just radar data that goes into a mets decision to issue a tornado warning. Knowledge of the near-storm environment is very important as well. For example, suppose a supercell is quite a way away from the radar, such that even the lowest 0.5 degree data are still a considerable distances above the ground. The supercell may have very strong rotation on the lower tilts, but, if the low-levels are very stable, the met may opt to hold back on a tornado warning since the chance of the supercell producing a tornado is significantly reduced. On the other hand, perhaps another nearby supercell is only 50 miles away but on the warm side of a warm front or differential heating boundary. In such a case, the near-storm environment of the 2nd supercell may be quite different than the 1st, which is something that the met is going to have to consider (or atleast SHOULD consider). It's not so much a function of the time of day (day vs. night), but of the low-level stability. In this case, low-level stability is often correlated with the time of day (less stable during the day; more stable at night), but it's really the low-level stability that often drives a decision as opposed to the time of day itself. After all, the low-levels may not stabilize much on some nights (perhaps there's rapid cyclogenesis occurring nearby, etc -- after all, we do see nocturnal tornado outbreaks sometimes).
Greg hinted at it with his last sentence -- there's more than just radar data that goes into a mets decision to issue a tornado warning. Knowledge of the near-storm environment is very important as well. For example, suppose a supercell is quite a way away from the radar, such that even the lowest 0.5 degree data are still a considerable distances above the ground. The supercell may have very strong rotation on the lower tilts, but, if the low-levels are very stable, the met may opt to hold back on a tornado warning since the chance of the supercell producing a tornado is significantly reduced. On the other hand, perhaps another nearby supercell is only 50 miles away but on the warm side of a warm front or differential heating boundary. In such a case, the near-storm environment of the 2nd supercell may be quite different than the 1st, which is something that the met is going to have to consider (or atleast SHOULD consider). It's not so much a function of the time of day (day vs. night), but of the low-level stability. In this case, low-level stability is often correlated with the time of day (less stable during the day; more stable at night), but it's really the low-level stability that often drives a decision as opposed to the time of day itself. After all, the low-levels may not stabilize much on some nights (perhaps there's rapid cyclogenesis occurring nearby, etc -- after all, we do see nocturnal tornado outbreaks sometimes).
On a purely radar perspective, when looking at Level2 vs. Level3 data, consider the images below of the same time periods. Besides the environmental and spotter inputs to the warning decision making process, the difference in datasets is obvious.
Mike Krzywonski
Thank you all for the great info. How beneficial would GRL2 be in addition to GRL3 for chasing?
GR2 takes too much bandwidth to use while chasing except in EVDO Rev.A areas... Meaning don't try, as it isn't going to happen...
James Siler
EF3
If I may add my radar question to this one as well, but I have seen this happen twice. But I have seen a tornado warning issued based on radar indications right after it passes over the radar and is riding that line where on radar shows the wind towards/away meet. Now cause of this, could the radar site be missing reading it. The example that sticks out in my head was about 2 weeks ago and the radar site was based in NW Louisiana. I tried to look at other radar sites to see a different vantage point but none could see the storm from there vantage point. Something I learned from alot of you after my little incident in 2007 north of Vici. Again this is something that I have been wondering. From what was posted above would the same decisions be put into process such as near storm enviroment and so forth. Thank you.
Greg Blumberg
EF4
I would assume that they are still using the same process and knowledge Jeff posted above with the storm environment. That's smart of you to check the other radar sites, BTW. Good call, even though it didn't provide you anymore information. Were you using the Base Velocity or the Storm Relative Velocity product? I know that the SRV can sometimes mask over that area and make it easier to see the storm. What resolution of radar data were you using? Level II or Level III?
It could also be that it was radar indicated primarily by the reflectivity and previous knowledge before the storm passed the radar. I would guess that the NWS office could be just being safe than sorry.
Could you provide a picture or something? It's hard to understand radar data by text, lol.
It could also be that it was radar indicated primarily by the reflectivity and previous knowledge before the storm passed the radar. I would guess that the NWS office could be just being safe than sorry.
Could you provide a picture or something? It's hard to understand radar data by text, lol.
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