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Severe Severe weather threat April 17-19

Tight couplet near puckettMSScreenshot_20190418-150722_RadarScope.jpg look at the donut hole to the southwestScreenshot_20190418-151012_RadarScope.jpg
 
My goodness lets hope this doesn't tighten up anymore. Its got A CC debris ball on it.Screenshot_20190418-151747_RadarScope.jpg
 
TXTornado said:
Waited up for that storm and was so underwhelmed. I am off 75, about 4 miles north of downtown and all we got was heavy rain and decent wind.
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I'm over east of Plano and the wind gust in Denton briefly had me intrigued but yeah it was pretty unimpressive. Rained more than I thought though
 
HRRR and RAP watching for east Alabama and West GA in the AM aint in clear yet parameters could be decent for strong winds and isolated tornados jusr a little north of I-20 still with the main concern is south of it
 
The 18z HRRR is just a textbook look at a mature, upshear-tilted QLCS accompanied by a strong rear-inflow jet (RIJ). Stratiform precipitation falling behind the most intense surface-based convection in addition to sublimation, melting, evaporation, & hydrometeor loading aloft all contribute to the intensity of the rear-inflow jet as well as the strength of the background flow regime. As long as there's strong deep-layer shear to tilt the downdrafts towards the rear of the surface-based convection, the rear inflow jet progressively intensifies as the QLCS ages & low-level cold pool grows stronger. Eventually, the RIJ may descend towards the surface, leading to very intense straight-line surface winds. You could probably imagine then why having a 100+ knot jet at 500 hPa overhead and high precipitable water in conjunction with mid-level dry air is a concern for straight line wind damage tomorrow here in NC because it strengthens the cold pools in the wake of the storms and thus also invigorating the RIJ and thereby increasing the wind damage potential.

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To add to what Eric posted, the HRRR 18z run intensifies the winds at 850mb progressively and by the time it reaches Eastern NC you have winds of 80kts at the 850mb level and 70kts only 1,000 feet off the ground. Insane.

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Webberweather53 said:
The 18z HRRR is just a textbook look at a mature, upshear-tilted QLCS accompanied by a strong rear-inflow jet (RIJ). Stratiform precipitation falling behind the most intense surface-based convection in addition to sublimation, melting, evaporation, & hydrometeor loading aloft all contribute to the intensity of the rear-inflow jet as well as the strength of the background flow regime. As long as there's strong deep-layer shear to tilt the downdrafts towards the rear of the surface-based convection, the rear inflow jet progressively intensifies as the QLCS ages & low-level cold pool grows stronger. Eventually, the RIJ may descend towards the surface, leading to very intense straight-line surface winds. You could probably imagine then why having a 100+ knot jet at 500 hPa overhead and high precipitable water in conjunction with mid-level dry air is a concern for straight line wind damage tomorrow here in NC because it strengthens the cold pools in the wake of the storms and thus also invigorating the RIJ and thereby increasing the wind damage potential.

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Not to mention the large round of convection moving in from the south in the late morning and the discrete cells just ahead of the main bands. The wind profile is much more supportive of tors through early afternoon before the trough approaches and winds become more unidirectional from the S and SSW. Anything in the late morning to mid afternoon will have to be watched if it develops away from any larger area of showers and storms.

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SD said:
Not to mention the large round of convection moving in from the south in the late morning and the discrete cells just ahead of the main bands. The wind profile is much more supportive of tors through early afternoon before the trough approaches and winds become more unidirectional from the S and SSW. Anything in the late morning to mid afternoon will have to be watched if it develops away from any larger area of showers and storms.

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That's been my concern as I watch the nam3k put out some convection along I95 and coastal plains as some look discrete.
 
Every single model continues to break the line apart somewhere near the Triangle tomorrow, before trying to reorganize it off to the east. It looks to be attributable to an earlier cluster of convection in that vicinity.
 
It seems the mobile alabama radar is down. Bad timing for it to be down.
 
Rain Cold said:
Every single model continues to break the line apart somewhere near the Triangle tomorrow, before trying to reorganize it off to the east. It looks to be attributable to an earlier cluster of convection in that vicinity.
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This is less than ideal
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SD said:
Not to mention the large round of convection moving in from the south in the late morning and the discrete cells just ahead of the main bands. The wind profile is much more supportive of tors through early afternoon before the trough approaches and winds become more unidirectional from the S and SSW. Anything in the late morning to mid afternoon will have to be watched if it develops away from any larger area of showers and storms.

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Yeah the environment pre-frontal looks better although the lack of a cap could even lead to rapid upscale growth well ahead of the line.
 
Something to look for tomorrow in the Carolinas regarding overall convective behavior: the disintegration of the line into isolated supercells &/or individual bowing segments will be largely dependent on the speed of the QLCS' cold pool which is related to the shear vector orientation to the long axis of the line and the amount of stratiform falling in the wake of the most intense surface-based convection. Parallel deep layer shear vectors & less stratiform precipitation >>> slower forward propagation of the QLCS cold pool >>> line of storms is more likely to break up into individual cells or segments, likely increasing the tornado threat & vis versa.
 
Shaggy said:
That's been my concern as I watch the nam3k put out some convection along I95 and coastal plains as some look discrete.
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Yeah the 3k actually has some streaks of updraft helicity with those. Hopefully the early arrival of those can keep the intensity down

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Webberweather53 said:
Yeah the environment pre-frontal looks better although the lack of a cap could even lead to rapid upscale growth well ahead of the line.
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Just looking at the 3k presentation you can kind of see how the early day stuff really gets going then it almost as quickly dies. Have to think as those cells merge they eventually just choke themselves out

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NWS BMX has changed there outlook. Moved the enhanced risk east and north along the I-20 corridor
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SD said:
Just looking at the 3k presentation you can kind of see how the early day stuff really gets going then it almost as quickly dies. Have to think as those cells merge they eventually just choke themselves out

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Yeah cell merges will definitely be a concern and w/ mid-level dry air around, the rear flank downdafts will likely be pretty cold and thus not terribly favorable for tornadogenesis but still could be just favorable enough support an isolated spin-up or two before the main event arrives.
 
SD said:
This is less than ideal
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Yes that is ugly. It’s hard to judge which would be worse: A cluster of storms with a couple of tornadoes or a lengthy squall line with 65 mph winds over a large area.
 
Expecting the highest tornado threat over the southern portion of alabama later were shear and instability is best. And the HRRR continues to indicate that a broken line of supercells will be over south alabama.20190418_171841.jpg
 
Webberweather53 said:
Yeah cell merges will definitely be a concern and w/ mid-level dry air around, the rear flank downdafts will likely be pretty cold and thus not terribly favorable for tornadogenesis but still could be just favorable enough support an isolated spin-up or two before the main event arrives.
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This seems to be raleighs thinking as well.

a plume of WAA-driven convection
streaming nwd from the Gulf Stream Atlantic will likely also be
ongoing over the NC Sandhills/Coastal Plain vicinity Fri morning.
Destabilization via advective processes may offset a lack of early
day diabatic heating owing to widespread low overcast, which may
contribute to the realization of around 1000 J/kg of MLCAPE there
through 15Z. Already strong, and strengthening deep layer flow would
favor some organization with this even early day activity, including
some rotating updrafts and risk of a brief/weak spin up.
 
Shaggy said:
This seems to be raleighs thinking as well.

a plume of WAA-driven convection
streaming nwd from the Gulf Stream Atlantic will likely also be
ongoing over the NC Sandhills/Coastal Plain vicinity Fri morning.
Destabilization via advective processes may offset a lack of early
day diabatic heating owing to widespread low overcast, which may
contribute to the realization of around 1000 J/kg of MLCAPE there
through 15Z. Already strong, and strengthening deep layer flow would
favor some organization with this even early day activity, including
some rotating updrafts and risk of a brief/weak spin up.
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Most recent HRRR depicting this well with what looks to be some morning supercells around
 
What I find interesting is the Hrrr soundings around upstate sc. has Tornado soundings. That’s interesting because it would be around 10am-12noon. Not much day time heading. What is causing this to spin up Tornados that early if the hrrr is correct?


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Rain Cold said:
Yes that is ugly. It’s hard to judge which would be worse: A cluster of storms with a couple of tornadoes or a lengthy squall line with 65 mph winds over a large area.
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This is kind of like figuring out which is worse between a very tightly wound very strong hurricane and a not as strong but much larger one. There's only so much energy available. Is that energy's effect extreme but very localized or is it less extreme but spread out and affecting more areas?
 
Jessy89 said:
What I find interesting is the Hrrr soundings around upstate sc. has Tornado soundings. That’s interesting because it would be around 10am-12noon. Not much day time heading. What is causing this to spin up Tornados that early if the hrrr is correct?


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I think this could be with the adjustment of the trough axis ... it seems as though when this line gets near Charlotte it begins to almost pivot and go negativity tilted ... charlotte looks to be on that inflection point of pivoting motion which could be aiding into that turning of the winds and the tornado soundings
 
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