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Convective Thread


weatherwiz

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On 6/13/2017 at 3:17 PM, weatherwiz said:

what's the VIL for the day?  Anyone still calculate that?  Albany used to mention it all the time in their AFD's but haven't seen that in quite some years.  

Trash that garbage. It has its uses, like assessing relative strength of storms compared to one another, but there are much better ways to interrogate a storm in real time. You are much better off setting dBZ thresholds to certain heights (i.e. the Donavon 50 dBZ height). A common one I use in addition to the 50 dBZ (because storms rarely hit that level in New England but still produce severe) is 55 dBZ to -23C, 60 to -17, and 65 to -7. Another common one is 70 dBZ over the freezing level, though sometimes that gets you a lot of pea size hail not large hail.

On 6/13/2017 at 3:28 PM, weatherwiz said:

Are these high CC values detecting hail?  Still trying to full understand CC/ZDR and how to analyze them on radar 

07CD23B4-A228-42F8-ABC7-4BDDD25061AB_zps

With hail detection you are looking for a few things. High dBZ helps, but with dual pol you want to focus on ZDR and CC. You will have ZDR near zero because hail tumbles as it falls. Tumbling hail will "average out" to be round (i.e. as wide and it is tall, 0 ZDR). Then you also want to see that collocated with low CC. You will have low CC because you are sampling an area with mixed hail and rain, and very different hydrometeor sizes.

We're starting to see signs that when you have high dBZ, near 0 ZDR, and CC that falls below like 0.80, it is favorable for significant hail.

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12 hours ago, OceanStWx said:

Trash that garbage. It has its uses, like assessing relative strength of storms compared to one another, but there are much better ways to interrogate a storm in real time. You are much better off setting dBZ thresholds to certain heights (i.e. the Donavon 50 dBZ height). A common one I use in addition to the 50 dBZ (because storms rarely hit that level in New England but still produce severe) is 55 dBZ to -23C, 60 to -17, and 65 to -7. Another common one is 70 dBZ over the freezing level, though sometimes that gets you a lot of pea size hail not large hail.

With hail detection you are looking for a few things. High dBZ helps, but with dual pol you want to focus on ZDR and CC. You will have ZDR near zero because hail tumbles as it falls. Tumbling hail will "average out" to be round (i.e. as wide and it is tall, 0 ZDR). Then you also want to see that collocated with low CC. You will have low CC because you are sampling an area with mixed hail and rain, and very different hydrometeor sizes.

We're starting to see signs that when you have high dBZ, near 0 ZDR, and CC that falls below like 0.80, it is favorable for significant hail.

Thanks for this information and explanation!!! This is great 

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6 hours ago, ineedsnow said:

Spc already has us in the day 4 outlook

Some people are going crazy bonkers talking widespread severe and possibility for isolated tornadoes lol.  This is a typical northeast severe setup...southwest flow, crappy lapse rates, modest instability thanks to dews/temps , and we do have solid shear.  I suspect scattered pockets of wind damage but nothing overly crazy 

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11 hours ago, weatherwiz said:

Some people are going crazy bonkers talking widespread severe and possibility for isolated tornadoes lol.  This is a typical northeast severe setup...southwest flow, crappy lapse rates, modest instability thanks to dews/temps , and we do have solid shear.  I suspect scattered pockets of wind damage but nothing overly crazy 

I'll say it has my attention when I see 50 knot flags popping up at 850 mb.

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26 minutes ago, OceanStWx said:

I'll say it has my attention when I see 50 knot flags popping up at 850 mb.

The shear is certainly there no doubt but I think we are really lacking better mid and upper level jet support.  The core of the jet streaks are well displaced from the warm sector and the warm sector is going to be characterized by poor lapse rates, good deal of cloud debris (but there will be plenty of breaks), and weakly capped.  There are some things on paper which look good but I think there are too many negatives to lead towards a bigger/widespread severe event.  

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14 minutes ago, weatherwiz said:

The shear is certainly there no doubt but I think we are really lacking better mid and upper level jet support.  The core of the jet streaks are well displaced from the warm sector and the warm sector is going to be characterized by poor lapse rates, good deal of cloud debris (but there will be plenty of breaks), and weakly capped.  There are some things on paper which look good but I think there are too many negatives to lead towards a bigger/widespread severe event.  

I definitely don't like the shear vectors being parallel to the front. That could mean more of flash flood threat than a severe threat.

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1 minute ago, OceanStWx said:

I definitely don't like the shear vectors being parallel to the front. That could mean more of flash flood threat than a severe threat.

Especially when you're talking PWAT values between 1.5''-2''.  That's just not good for severe either...cape gets water loaded and we're already looking at skinny cape profiles with crappy lapse rates in place.  Given degree of shear, if buoyancy isn't strong enough updrafts can have a real tough time growing tall enough...even if we had like 1500-2000 SBcape b/c of water loading without the better mid/upper jet support.  

We have had plenty of similar setups before and I remember I used to get so pumped for them but they never panned out to how some (including myself) panned them out to be.  I'm sure there will be severe weather...it just isn't going to be anything overly eye opening.  However, maybe we can spin up a HV special? 

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2 hours ago, OceanStWx said:

50 knot 850s FTW. Day 3 enhanced, that's pretty rarefied air for New England. Even clips a bit of Hartford County there.

Was going to say, can't remember seeing a Day 3 enhanced before in this neck of the woods. A slight at that range is usually the best we can ask.

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1 minute ago, Hoth said:

Was going to say, can't remember seeing a Day 3 enhanced before in this neck of the woods. A slight at that range is usually the best we can ask.

Obviously not an apples to apples comparison here, but the SPC has frequently used the example that 6/1/11 would have been an enhanced across much of the Northeast based on their probabilities.

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