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Spring/ Summer 2014 Convection Discussion


weatherwiz

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Well with that info I guess I could give a bit more of our experience...choose not to at the time b/c people think I'm nuts but during that time of wind shift it felt extremely weird and my friend and brother said they both felt their ears kind of pop at the same time...I didn't notice if that happened to me but there was a moment of really weird silence before winds gusted up again...idk just stating what we experienced

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Was a survey done?  Just curious why you specify EF1

 

Don't know for sure... just a hunch. Have seen dozens of pics and video and there's a lot of solid tree damage but virtually no structural damage. Generally would fit in with EF-1 kind of damage... though I can't say for sure. 

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Ryan can you post a comparison of the ZDR image before tornadogenesis? Just trying to see the difference of how it looks prior to genesis and during genesis.

 

This isn't a great case.... and I could be wrong... but there is some signs that there's some size sorting of hydrometeors going on as the low level shear strengthens. I've posted the 0.5 degree slice from OKX at 2250 UTC and 2255 UTC.

 

post-40-0-25909600-1401297406_thumb.png

 

At 2250 UTC as the low level meso first appears notice that all the higher ZDR echoes (lower left... yellow >2 db and red >3 db) are in the rear part of the storm.. and a lot of that is coincident with high kdp (yellows/oranges in the bottom right).

 

post-40-0-34772900-1401297416_thumb.png

 

When you fast forward 5 minutes you have a clear inflow notch in reflectivity, a strong low level mesocyclone (60+ knots gate to gate) and a pocket of high ZDR that appears just east of the mesocyclone in the forward flank of the storm. The high ZDR is out in front of the high KDP now and there are some pixels of ZDR >4 dB. That is a signal that you could have seen some size sorting of the hydrometeors going on here with the larger drops (that have a high differential reflectivity... the drops become oblate and look like hamburger buns) while the smaller drops get carried into the back of the storm and you get a separation between a few big drops with overall low liquid water content in the southern portion of the storm (along the reflectivity graident) and a lot of smaller drops farther back in the storm.

 

Does that make sense?

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This isn't a great case.... and I could be wrong... but there is some signs that there's some size sorting of hydrometeors going on as the low level shear strengthens. I've posted the 0.5 degree slice from OKX at 2250 UTC and 2255 UTC.

 

attachicon.gif2250.png

 

At 2250 UTC as the low level meso first appears notice that all the higher ZDR echoes (lower left... yellow >2 db and red >3 db) are in the rear part of the storm.. and a lot of that is coincident with high kdp (yellows/oranges in the bottom right).

 

attachicon.gif2255.png

 

When you fast forward 5 minutes you have a clear inflow notch in reflectivity, a strong low level mesocyclone (60+ knots gate to gate) and a pocket of high ZDR that appears just east of the mesocyclone in the forward flank of the storm. The high ZDR is out in front of the high KDP now and there are some pixels of ZDR >4 dB. That is a signal that you could have seen some size sorting of the hydrometeors going on here with the larger drops (that have a high differential reflectivity... the drops become oblate and look like hamburger buns) while the smaller drops get carried into the back of the storm and you get a separation between a few big drops with overall low liquid water content in the southern portion of the storm (along the reflectivity graident) and a lot of smaller drops farther back in the storm.

 

Does that make sense?

 

Yeah I see that and it does makes sense...at least to me anyways. I just wanted to see an example of before and after...I've seen the papers on the actual ZDR arc thanks to your chat with Chris the other day...but that's a pretty cool example there, even if it's not textbook. 

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Yeah I see that and it does makes sense...at least to me anyways. I just wanted to see an example of before and after...I've seen the papers on the actual ZDR arc thanks to your chat with Chris the other day...but that's a pretty cool example there, even if it's not textbook. 

 

I think this will also be a case where you had a relatively small tornado in New Milford/Bridgewater that moved SE but most of the damage was by far was from the RFD and the eventual collapse of the cell/downburst that lead to some intense winds. OKX had a pretty good swatch of 50+ knots on radial velocity as the storm moved into Southbury, Sandy Hook, and Monroe. 

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I think this will also be a case where you had a relatively small tornado in New Milford/Bridgewater that moved SE but most of the damage was by far was from the RFD and the eventual collapse of the cell/downburst that lead to some intense winds. OKX had a pretty good swatch of 50+ knots on radial velocity as the storm moved into Southbury, Sandy Hook, and Monroe.

Same thing you mentioned that happened in the TOR last summer. I remember you said it was mostly caused by the RFD
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A few rumbles here last evening as well. Two day rain total thus far is 0.97". BDF heaven, 44.8°F.

 

Two day precip total 0.88", now at exactly 4.00" for the month.  Avg for May is 4.33", so we'll be pretty close.  No rumbles nor flashes for me yet.  Latest in the year I've gone here w/o thunder is June 5, in 2003.  This year might be a contender. 

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This isn't a great case.... and I could be wrong... but there is some signs that there's some size sorting of hydrometeors going on as the low level shear strengthens. I've posted the 0.5 degree slice from OKX at 2250 UTC and 2255 UTC.

 

attachicon.gif2250.png

 

At 2250 UTC as the low level meso first appears notice that all the higher ZDR echoes (lower left... yellow >2 db and red >3 db) are in the rear part of the storm.. and a lot of that is coincident with high kdp (yellows/oranges in the bottom right).

 

attachicon.gif2255.png

 

When you fast forward 5 minutes you have a clear inflow notch in reflectivity, a strong low level mesocyclone (60+ knots gate to gate) and a pocket of high ZDR that appears just east of the mesocyclone in the forward flank of the storm. The high ZDR is out in front of the high KDP now and there are some pixels of ZDR >4 dB. That is a signal that you could have seen some size sorting of the hydrometeors going on here with the larger drops (that have a high differential reflectivity... the drops become oblate and look like hamburger buns) while the smaller drops get carried into the back of the storm and you get a separation between a few big drops with overall low liquid water content in the southern portion of the storm (along the reflectivity graident) and a lot of smaller drops farther back in the storm.

 

Does that make sense?

 

Really interesting stuff

 

Considering the inbound velocity max at 2255 is trailing the center of rotation and may be associated with a collapsing core (note the weakening of the reflectivity NNW of Washington at 2250) I wonder if near ground winds advecting into the vicinity of the meso may have enhanced lift in general on the front flank.   Horizontal sorting in an event dominated by storm motion I would expect to be very evident on the inbound side, which it is to some extent as your annotation indicates, but in this case the ZDR increase seems more widespread.  Of course, vertical vorticity associated with a tightening meso could also do that....

 

At any rate, nice post.  Do you have SRV?

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This isn't a great case.... and I could be wrong... but there is some signs that there's some size sorting of hydrometeors going on as the low level shear strengthens. I've posted the 0.5 degree slice from OKX at 2250 UTC and 2255 UTC.

 

attachicon.gif2250.png

 

At 2250 UTC as the low level meso first appears notice that all the higher ZDR echoes (lower left... yellow >2 db and red >3 db) are in the rear part of the storm.. and a lot of that is coincident with high kdp (yellows/oranges in the bottom right).

 

attachicon.gif2255.png

 

When you fast forward 5 minutes you have a clear inflow notch in reflectivity, a strong low level mesocyclone (60+ knots gate to gate) and a pocket of high ZDR that appears just east of the mesocyclone in the forward flank of the storm. The high ZDR is out in front of the high KDP now and there are some pixels of ZDR >4 dB. That is a signal that you could have seen some size sorting of the hydrometeors going on here with the larger drops (that have a high differential reflectivity... the drops become oblate and look like hamburger buns) while the smaller drops get carried into the back of the storm and you get a separation between a few big drops with overall low liquid water content in the southern portion of the storm (along the reflectivity graident) and a lot of smaller drops farther back in the storm.

 

Does that make sense?

 

We took a long look at yesterday and the ALY tornado day in our office workshop today. Always nice to rehash it, because you see things you didn't necessarily see the first time around.

 

The SPC SSEO (http://www.spc.noaa.gov/exper/sseo/) essentially nailed the areas for severe convection both days. If you use updraft helicity as a proxy for supercells, it narrowed the focus down the areas where these significant storms went. Like any other products, I wouldn't take them verbatim. However, as far as general area and evolution goes they are a great tool.

 

Then going back through the ALY tornado, despite mesoanalysis showing marginally favorable parameters, the 88D storm relative winds into that supercell were about 50 kts at 250 ft.

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Well no tornado, but dual-pol did show a rapid increase in shear based on what Ryan showed. That kind of mesocyclone can definitely drive a pressure induced RFD up to those wind speeds.

 

Yeah most of the damage (even if there was a touchdown) would have been from the developing RFD anyway. Impressive low level mesocyclone and storm. 

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Really interesting stuff

 

Considering the inbound velocity max at 2255 is trailing the center of rotation and may be associated with a collapsing core (note the weakening of the reflectivity NNW of Washington at 2250) I wonder if near ground winds advecting into the vicinity of the meso may have enhanced lift in general on the front flank.   Horizontal sorting in an event dominated by storm motion I would expect to be very evident on the inbound side, which it is to some extent as your annotation indicates, but in this case the ZDR increase seems more widespread.  Of course, vertical vorticity associated with a tightening meso could also do that....

 

At any rate, nice post.  Do you have SRV?

 

I'll get the SRV posted tomorrow... I can do it off GR. 

 

Both the New Milford CT case from yesterday and to a bigger extent Amsterdam NY did seem to indicate hydrometeor size sorting was going on but both times the signal happened almost simultaneously with the onset of the tornado/low level meso on radar. Really wouldn't help a radar op in either case since the velocity sig was the really big clue. 

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I'll get the SRV posted tomorrow... I can do it off GR. 

 

Both the New Milford CT case from yesterday and to a bigger extent Amsterdam NY did seem to indicate hydrometeor size sorting was going on but both times the signal happened almost simultaneously with the onset of the tornado/low level meso on radar. Really wouldn't help a radar op in either case since the velocity sig was the really big clue. 

 

I think down the road plans would have some sort of alarm go off on our workstations when the separation reaches a certain threshold. Similar to what happens with meso alarms now.

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Possibly. What we really need is the next radar build upgrade which will include dual-pol with SAILS.

 

Can't wait for SAILS. Why don't more WFOs utilize AVSET more? There seem to be many cases where it can be used but isn't for some reason. 

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Can't wait for SAILS. Why don't more WFOs utilize AVSET more? There seem to be many cases where it can be used but isn't for some reason. 

 

That's a good question. I think AVSET is great. I mean after a certain point storms get close enough that the volume scan will go all the way through 19.5 anyway, but why not have it on through that point?

 

SAILS will slide right into AVSET as well, where it will find the middle of whatever the AVSET volume scan is.

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