rdale
EF5
True, but the general public doesn't give a boot about moderate risk verifications.
4/18/13 What Happened?
- Thread starter Matt Hunt
- Start date
Rob H
EF5
People might be surprised at how many significant tornadoes occurred in 500-1000 J/Kg MLCAPE. Tornadic storms require a balance of ingredients, and the balance was slightly off for this setup. That balance allows for extreme shear to compensate for weaker instability, and vice versa, in many cases. Statistically speaking, the average for sig tors in southern IN seems to be ~860 J/Kg MLCAPE. Just a little more clearing, and it easily could have hit that on the day in question.
I'm not saying I wasn't scratching my head at the PDS tor watch - just that huge instability isn't needed for sig tors. Certainly more than 250 or whatever the archived mesoanalysis is showing is needed, however.
I'm not saying I wasn't scratching my head at the PDS tor watch - just that huge instability isn't needed for sig tors. Certainly more than 250 or whatever the archived mesoanalysis is showing is needed, however.
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Matt Hunt
EF3
STexan; I have noticed as well that the models seem to be over-estimating many of the parameters, even up to just a few hours before the event. I have mainly looked at the RAP on the day of, but on Thursday the HRRR was breaking out semi-discrete cells in southern IL/IN for a couple runs around the 20z timeframe. The RAP showed over 2000 J/kg CAPE in some areas, including northern IN. I don't recall the exact run times, but I believe this was around the 10z run. In order for that to have become a reality, the initial squall line would have needed to dissipate, and the clouds clear out. I also noticed that hodographs in my target area looked much better early in the morning, and as the day went on got worse and worse. I don't think it was so much that they were showing a BIG day, but they certainly were showing more than just rain showers.
Rob Hurkes: I like the way you worded it, as it is a balance of the ingredients. That was one thing that I was optimistic about, is that it doesn't always require a lot of CAPE as long as the shear is there. Even with the better shear that models showed early on, I still didn't think it was enough for a PDS watch. Most of it was in the very lowest levels, and it was a lot of speed shear, with only a little bit of directional shear. So while instability was lacking, perhaps a lack of more adequate shear was also a major factor in this event busting.
Rob Hurkes: I like the way you worded it, as it is a balance of the ingredients. That was one thing that I was optimistic about, is that it doesn't always require a lot of CAPE as long as the shear is there. Even with the better shear that models showed early on, I still didn't think it was enough for a PDS watch. Most of it was in the very lowest levels, and it was a lot of speed shear, with only a little bit of directional shear. So while instability was lacking, perhaps a lack of more adequate shear was also a major factor in this event busting.
Tim Carley
EF0
Skip, I understand that forecasters are very aware of "Warning/Watch Fatigue". Do you think that if these same parameters were present in the middle of a very busy, violent storm season a PDS would still have been issued?
Skip Talbot
EF5
I'm probably not the best person to answer that question. Do you mean that the SPC forecaster was more inclined to use a PDS watch because the season has been relatively quiet so far? I'd hope that isn't the case and instead they're looking more at the parameters and analysis of the specific event rather than how the season is trending to make those decisions. I don't have a meteorology degree, however, and I also don't know many of the policies of the NWS and SPC so someone else here could probably better answer that. As was stated by others, I think variation between forecasters, and the details of the setup itself were the reason for the PDS. I'd be surprised if the number of watches or warnings previously issued for the year was factored in.
I'd be willing to bet money there is some of that going on. I've seen cases in which some events seem to get much higher risk designations and stronger wording relative to a similar event (CAPE and shearwise) during a different part of the year. I think the population and placement of large cities within a risk area and the departure in time of the risk from when typical climatological peak activity occurs influences risk designations.
rdale
EF5
That was not the case in this event.
You know this for fact, or are you just assuming?
rdale
EF5
Yes, I know this for a fact. Related to my earlier post.
If you know the PDS issuance was intentional, can you please enlighten the rest of us as to why?
Chris_Spannagle
EF0
Hi Jeff,
I've talked with someone at SPC about the watch. The PDS wording was requested by the affected forecast offices is what I was told. What they saw or why the requested the wording I'm not sure but that's what I was told.
