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Wednesday, July 22, 2020 and/or Thursday, July 23, 2020 Severe Threat


weatherwiz
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3 hours ago, Henry's Weather said:

Thanks. More questions, not necessarily only aimed at weatherwiz: In my (limited) understanding,  EML air-masses originate from the SW USA and find their way here along a ridge with westerly winds usually? And they're characterized by dry midlevels and steep midlevel lapse rates? If this is true, and transport is usually due to a midsummer 594-ish mb ridge, I'm wondering why these events aren't that common. It seems like we get ridges like that a couple times every summer, and we see frontal passages maybe every 4 days.

Correct, more often than not if you do a trajectory trace, our EML's derive from the southwestern U.S. I mean you can also get a bit more technical and say more the southern-tier of the Inter-mountain West region.

You are correct, these are characterized by very dry mid-levels with sharp warming usually around 800mb-700mb then a rapid decrease of temperature with height above that (hence the steep lapse rate. And yes, typically they will traverse the crest of strong mid-level ridging with a westerly-to-northwesterly flow in the mid-levels. 

As for why they aren't more common the biggest factors really is the Gulf of Mexico and convective overturning. East of the Mississippi River (perhaps maybe even a bit farther west than this) the Gulf of Mexico is a major contributor to the climate of this region. For example, if you were to look at a national annual rainfall map you would see a significant gradient right around the Mississippi River. Warm/moist air from the Gulf of Mexico transporting northward (especially when you have a deep southerly flow) disrupts the structure of the EML so the capping associated with that warm layer is weakened which promote more mixing. 

In terms of convection, when you have widespread convective events you get outflow boundaries, convective overturning, latent heat release, turbulence, etc...all of these promote mixing which degrades the integrity of the EML. 

Michael Ekster (I also think radarman was an author as well) wrote a paper about 10-years ago regarding EML advection into the Northeast. It seems the best synoptic configuration for an EML to maintain it's integrity into our region was to have a strong 700mb height anomaly in the southeast U.S. (with the strongest anomalies I think in the TN Valley region) with a trough digging into the western U.S. This flow seemed to promote the northward transport of EML air farther north into the northern Plains...even into Canada where it is farther removed from the Gulf of Mexico, thus limiting potential influences from this moisture source. Also, this seemed to be yield the maintaining of the cap associated with the EML preventing mixing. 

There was also something else of interest too...actually will have to go back and refresh my memory on this but there was something weird about the trajectory course of previous EML events studied where the trajectory did a loop...at the time it wasn't sure what this was and why. 

 

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5 minutes ago, Whineminster said:

Hearing boom booms in the bedroom?

lol.

Doesn't seem like much consistency for tomorrow...RPM for example blows a line through afternoon through mid-evening while 3km NAM is much later. I'm wondering if we could see two rounds...mid-to-late aftn with additional scattered development during the evening and overnight. 

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SPC obviously implements a variety of different tools to reveal risk areas that blah blah formulate their products, but ... just analyzing the NAM's last three cycles of trends for the basics ... the better of the two days is clearly Wednesday if using that guidance. 

You know back in the day ... a little known model factoid of excruciatingly nerdy tedium was that the then "ETA" model was a spectacular tool for "convection initialization" ... Oh, perhaps not down at the discrete level of what exact CU tower glaciated... but, it tended to perform well inside of 30 ... 36 hours, by depicting QPF distribution ...then convective attribute verification took place.  'Talking mid 1990s in the Plains ...but that was in general true. 

The ETA being the ancestral root of the NAM ( ...and notwithstanding it passed through the WRF bad-idea man-handling years too...), one could only guess if that esoteric obscurity still is true? I could see it being the case, and say... no one including SPC's even is aware of it any longer...Shit, considering the present day work force is headed up by my generation of slackers and cheaters?? Not much confidence such an obscurity even floats off-the-cuff conversation but ...I'm also an assholey cynic for recreation, too.  Heh.  But then again, the general dumbing down of higher order intellect running the world got us a narcissist, if not a patented sociopath into the most powerful sociological position ever to man a post of authority spanning 750,000 years of Human evolution, so... the evidence is damning; we live in an increasingly automated systemic modernization of conveniences ... addling the population-fluid into an unchallenged soup of e-zombies...  Or, they're all geniuses ... tru dhat -

Firstly, just as a personal experience ... back-to-back severe days in New England are exceedingly rare.  The title of this thread is suspect and shamelessly wanton of bun-dom...

Why? there are varied textured reasons for that.  Just in a general mean, the synoptics that are needed for convection anywhere really are fragile ... It's just so uniquely favorable to load up those variables in the Plains it deludes us into thinking it's easy...That region is just perfectly designed geomorphologically to feed that - the Earth backing that region is like enabling.. like entitlement.

Babbling...  but the NAM's last three runs paint as though a right exit region of a 500 mb jetlett encroache upon the upper MA and SNE/CNE after 18z Wednesday ... consistently. Meanwhile, there is instra-model contention on handling the brambled mangled twisted pressure pattern from central NJ to S ME during Wed afternoon, with mottled light QPF nodes per run... That's pretty easily interpretable as a warm frontal diffusion and trouble in the guidance with that particular lead environment ..but I like that!  You want light S tendencies along a diffused warn front, because... if we get some sky lights and warm the lower levels, we end up with SB CAPE under/within a positive direction shear...and then accelerate mid levels from the W..?. Our bulk shear thru deeper 0-6km over the top of the 0-3km SRH along warm frontal intrusion ... That looks like super cell potential to me SE PA to N. NJ... and probably bowing linear rip in CT and MA to southern VT ... It's not like a high risk or anything...but that 50kts of jet nosing in over substantive heating...with a lead side diffused warm boundary lifting toward CNE during the day ... plus, the hydrostatic layout ( heights) show some cyclonic orientation as well as a smidge of lowering toward and after 21z west to E ...

This will probably then process the atmosphere out ...the next day may see late blooming activity as the southern end of the vestigial trough sharpens and we see the cyclonic curved flow accelerate again through 50 kts east of ALB around and post 21z on Thursday, but CAPE and previous day...  it could be mechanical forcing.. 

Of course...that's what I'm seeing in the NAMs general last three runs...  Who knows what extra-double, top-secret surreptitious convective-salacious sexy instrumentation they use that we don't even know about so that they look better than the increasingly tool-savvy public..  

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well...so, SPC echoes my thoughts above - whether they use other tools than the NAM or not...heh

 

https://www.spc.noaa.gov/products/outlook/day2otlk.html

 

"... Bowing line segments and clusters should be the dominant storm mode,
   with damaging wind gusts as the predominant severe threat.
   Deep-layer vertical shear decreases with southern extent, so the
   highest potential for more organized storms, and perhaps even a few
   supercells, exists from central PA into Upstate NY/Southern New
   England. In this area, the stronger vertical shear suggest slightly
   greater potential for hail and maybe even a tornado or two.
   Antecedent cloud cover and possibly a few showers could inhibit
   destabilization in the vicinity of the warm front, but the stronger
   shear still merits including this area in a 15% wind probability...."

either way ...expansion of the SLIGHT area is warranted in my estimation as the general region still benefits from a theta-e stranded by only weak antecedent frontal tapestries ... and, now we're running 40 to 50 kt wind max over a sensy lapse rate... kind of a slam dunk... Throw in Lakefront and oreographic triggers and there we go.

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18 minutes ago, Typhoon Tip said:

well...so, SPC echoes my thoughts above - whether they use other tools than the NAM or not...heh

 

https://www.spc.noaa.gov/products/outlook/day2otlk.html

 


"... Bowing line segments and clusters should be the dominant storm mode,
   with damaging wind gusts as the predominant severe threat.
   Deep-layer vertical shear decreases with southern extent, so the
   highest potential for more organized storms, and perhaps even a few
   supercells, exists from central PA into Upstate NY/Southern New
   England. In this area, the stronger vertical shear suggest slightly
   greater potential for hail and maybe even a tornado or two.
   Antecedent cloud cover and possibly a few showers could inhibit
   destabilization in the vicinity of the warm front, but the stronger
   shear still merits including this area in a 15% wind probability...."

either way ...expansion of the SLIGHT area is warranted in my estimation as the general region still benefits from a theta-e stranded by only weak antecedent frontal tapestries ... and, now we're running 40 to 50 kt wind max over a sensy lapse rate... kind of a slam dunk... Throw in Lakefront and oreographic triggers and there we go.

I think they read your post.

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9 minutes ago, Damage In Tolland said:

Today’s threat is mainly SW of SNE. Maybe a few evening storms but not severe . Tomorrow afternoon looks like best chances are north and east of the Pike 

western CT is certainly at risk...between 5:00 PM and 8:00 PM. Need to watch those storms closely too

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I think things are coming along very well...if not even better for CT. Despite some of the clouds around there is significant clearing/breaks and 70's dews are racing northward. Also looks like shear may end up being a bit stronger than modeled too. Really need to watch between 5-8 for some discrete supercells 

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11 minutes ago, weatherwiz said:

I think things are coming along very well...if not even better for CT. Despite some of the clouds around there is significant clearing/breaks and 70's dews are racing northward. Also looks like shear may end up being a bit stronger than modeled too. Really need to watch between 5-8 for some discrete supercells 

1630 OTLK wasn't favorable for N PA into NY per disco fyi

   The evolution farther north in northern PA/southern NY is more
   uncertain due to abundant clouds that are overspreading the area
   from the west.  This area has the strongest winds aloft and large
   scale forcing, so a conditional risk of severe storms persists if
   deep convection can develop.  Chose not to modify the ongoing
   forecast due to the conditional threat, but confidence in severe
   storms has diminished somewhat in parts of north-central PA and
   south-central NY.

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