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Wednesday, October 7, 2020 Convective Potential


weatherwiz
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Trees taking down wires is going to be a big issue for a long time and it ill probably get worse. So many trees are dying off from ash borer, gypsy moths, disease/drought etc. Millions of Ash are going to die off over the next few years from EAB alone. Just look around at how many dead trees there are everywhere just waiting to fall on lines. Trees are extremely expensive to remove. There's going to be millions of dead ones that need to be cut down with no money to pay for it. 

 

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On 10/7/2020 at 5:57 PM, weatherwiz said:

I always forget but I am not sure if the distance requirement is the same for the classification of each type (serial, progressive, and hybrid). I think the criteria may be a bit more loose for serial derechos. 

Yeah not so sure about the criteria. I've always used 240 miles as my benchmark. Another thing I noticed was dew points were only in the 50's with this serial derecho I wonder if that classifies it as a low dew point derecho. Does anyone know the threshold on that?

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2 hours ago, It's Always Sunny said:

Yeah not so sure about the criteria. I've always used 240 miles as my benchmark. Another thing I noticed was dew points were only in the 50's with this serial derecho I wonder if that classifies it as a low dew point derecho. Does anyone know the threshold on that?

According to this paper: https://www.spc.noaa.gov/publications/corfidi/ldd_2006.pdf  it's below 50 and/or pwat<.5:

   "More rarely, high-wind-producing MCSs occur in en-vironments of very limited moisture, with surface dew-points at or below 50°F (10°C) and/or precipitable wa-ter less than 0.5 in. (1.25 cm). Systems forming in suchenvironments, herein referred to as low-dewpoint dere-chos (LDDs), have been observed throughout much ofthe year and over much of the United States from theGreat Basin to the East Coast. "

Personally I would guess that this event might be classified as a hybrid serial/low-dewpoint derecho. If that is a thing.

 

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10 hours ago, It's Always Sunny said:

Yeah not so sure about the criteria. I've always used 240 miles as my benchmark. Another thing I noticed was dew points were only in the 50's with this serial derecho I wonder if that classifies it as a low dew point derecho. Does anyone know the threshold on that?

 

8 hours ago, ct_yankee said:

According to this paper: https://www.spc.noaa.gov/publications/corfidi/ldd_2006.pdf  it's below 50 and/or pwat<.5:

   "More rarely, high-wind-producing MCSs occur in en-vironments of very limited moisture, with surface dew-points at or below 50°F (10°C) and/or precipitable wa-ter less than 0.5 in. (1.25 cm). Systems forming in suchenvironments, herein referred to as low-dewpoint dere-chos (LDDs), have been observed throughout much ofthe year and over much of the United States from theGreat Basin to the East Coast. "

Personally I would guess that this event might be classified as a hybrid serial/low-dewpoint derecho. If that is a thing.

 

ahhh great point...I didn't even consider about low-dewpoint derecho. But I also do believe the distance criteria is probably standard throughout...although given how this went to the coast I would say this met criteria. 

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Times Union newspaper in Albany had an article stating the NWS believes 100mph gusts were reached in their CWA.

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National Weather Service scientists observed “steel girders holding up a large billboard bent to the point that the billboard was almost horizontal with the ground, structural damage to a saw mill, numerous power poles leaning, and numerous trees uprooted,” according to their preliminary observation after the storm.

Those conditions suggest a gust of 100 mph likely tore through there at 3:56 p.m.

Other potential winds on Wednesday included an estimated 90 mph gust in Pittstown and an 80 mph one in Root, Montgomery County, noted Joe Villani, a meteorologist for the National Weather Service in Albany.

 

 

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My folks got power back in the Albany suburbs this weekend after 3.5 days without.  That's an unheard of amount of time for a power outage in that area.  I don't think growing up there I can remember anything more than just a single night without power.  It's full on suburbia there, power outages always seemed extremely rare.  Lots of underground lines, trees cut well back from lines, etc.

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2 hours ago, powderfreak said:

My folks got power back in the Albany suburbs this weekend after 3.5 days without.  That's an unheard of amount of time for a power outage in that area.  I don't think growing up there I can remember anything more than just a single night without power.  It's full on suburbia there, power outages always seemed extremely rare.  Lots of underground lines, trees cut well back from lines, etc.

Move to CT if you want some real power outages.

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I've been messing around with data from the event, trying to tease out what, if any, lead time we (NWS) might have been able to provide with the scale and scope. The messaging was definitely not convectively driven.

In high shear/low CAPE environments Sherburn has done a lot of work to try and craft a parameter to hone in on the highest risk areas. SPC hosts a couple of those (SHERBE and modified version) that use the variables most correlated to significant severe weather in that environment. The 7th certainly qualified as HSLC.

I ended up outlining the 1.5 unit SHERBE area and overlaid it on the SPC reports and the results were pretty damn good. 

SHERBE_Reports.png?width=1920&height=108

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That's not to say this alone could've clued mets into how the event was going to unfold, but once the convective threat was identified the max SHERBE values certainly highlighted the area most at risk for significant severe (and I would say that multiple ASOS gusts near 60 knots while not technically significant by SPC definitions is pretty damn significant for these parts). 

Some of the subtle differences I saw between guidance and observations included slightly greater separation between the lead light rain/cloud cover and the convective line. This allowed low level lapse (key variable for SHERBE!) rates to be higher than forecast. Unfortunately I don't have any forecast graphics of LLLR, only objective analysis from SPC, but I can get point values from Bufkit and compare to SPC. They generally were forecast 6-18 hours prior to the event around 6 to 6.5 C/km, but SPC indicates that they may have been pushing 7.5 by go time.

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