• Hello, please take a minute to check out our awesome content, contributed by the wonderful members of our community. We hope you'll add your own thoughts and opinions by making a free account!

Severe Severe weather threat April 17-19

The HRRR did well with the last threat so we’ll see tomorrow. I’m not buying the NAM.


Sent from my iPhone using Tapatalk
 
With limited computer analysis, I can report massive SSE inflow from Orange Beach directly off the Gulf!!!! This just feels “ominous”. IMHO


Sent from my iPhone using Tapatalk
 
3km nam indicates a lot deeper of a low than the LR HRRR. And more of a broken line which would increase the tornado risk. Doubt this happens but something to watch. And also see how high dew points can make it and instability.
nam3km_mslp_pcpn_frzn_seus_29.png
 
0z models don't look very impressive to me. I just feel that the morning junk is gonna get in the way, and storm mode will be very messy. Maybe some straight line winds for sure, but will be surprised to hear multiple tornadoes.
 
Nick_boynton_ said:
Anyone got some analysis on NC threat for Friday?
Click to expand...

Messy storm modes, VBV, meh critical angles, low topped supercells/QLCS, best backing of the winds over central/eastern Nc supporting a tornado risk there, damaging winds threat due to a strong LLvl jet and storms tapping into that dragging the strong winds downward + dry air aloft, not much has changed
 
Myfrotho704_ said:
Messy storm modes, VBV, meh critical angles, low topped supercells/QLCS, best backing of the winds over central/eastern Nc supporting a tornado risk there, damaging winds threat due to a strong LLvl jet and storms tapping into that dragging the strong winds downward + dry air aloft, not much has changed
Click to expand...
Thanks! Looks like spc will probably keep enhanced for day 2 then
 
oh now it gets interesting lol and not for hail at all

next county over :rolleyes:

...A SEVERE THUNDERSTORM WARNING REMAINS IN EFFECT UNTIL 1230 AM CDT
FOR DENTON COUNTY...

At 1140 PM CDT, a severe thunderstorm was located over Denton, moving
east at 45 mph.

This is a very dangerous storm.

HAZARD...80 mph wind gusts and quarter size hail.

SOURCE...Denton Airport measured 73 MPH winds around 11:35 PM.
 
Anyone have any insight as to what central Georgia will be looking at?

Local mets mention that there is a chance of strong to severe storms with wind, hail, and brief isolated tornadoes but no mention of timing, intensity, or any other important info.

Mostly wondering if I’m looking at a nocturnal threat or if the bad stuff will hold off until morning.
 
day1otlk_1200.gif

day2otlk_0600.gif
 
First time I've seen a sounding like this. The 3km NAM is showing pockets in the LLJ where the winds exceed 80kts in Eastern NC Friday evening.

1555590504255.png

This sounding was taken from the bright yellow spot near Jacksonville. The 850mb winds are widespread 70-85kts across Eastern NC and checking soundings the 925mb winds appear to be in the 60-65kt range with pockets much higher than that in or near any storms.

850mb .jpg

IMO the main threat with this one is going to be strong winds, especially over Eastern NC where the winds only 1,000 feet up are howling at 60-65kts on guidance. There won't be much instability to work with, I'm thinking around 1,000-1,500 during the day but it also won't take much to bring these strong winds down to the surface. With the saturated ground we have this will enhance the threat as trees will be more susceptible to being blown over. Not to mention our local NWS offices are saying winds will be gusting in the 30s to near 40 before the storms even arrive Friday afternoon/evening.
 
Also one of my favorite tools to use to pick out areas that have the highest risk of severe weather is the updraft helicity tool. I've found this pretty useful for events like this especially where a line of storms may develop. The HRRR is highlighting a very strong line of storms in central to northern AL/MS.

HRRR.jpg
 
Looks like most models break the line apart as it gets into central sections of NC. Even the latest NAM is unimpressive. That's not to say that there won't be any wind reports, but I'm starting to wonder if we'll actually see an organized squall line moving through. The RAH AFD is impressive and the expansion of the Enhanced Risk area by SPC is noteworty, but virtually all of the models backed off of the intensity of the line through central NC. It reorganizes east of 95. If this continues, I wouldn't be surprised to see the SPC back off on the Enhanced Risk somewhat in the next Day 2 outlook.
 
Rain Cold said:
Looks like most models break the line apart as it gets into central sections of NC. Even the latest NAM is unimpressive. That's not to say that there won't be any wind reports, but I'm starting to wonder if we'll actually see an organized squall line moving through. The RAH AFD is impressive and the expansion of the Enhanced Risk area by SPC is noteworty, but virtually all of the models backed off of the intensity of the line through central NC. It reorganizes east of 95. If this continues, I wouldn't be surprised to see the SPC back off on the Enhanced Risk somewhat in the next Day 2 outlook.
Click to expand...
They’re almost definitely not going to back off the day 2 outlook just based on cam evolution at this stage, it would be more of a concern if we were actually on the day of the event and had actual obs to confirm or deny the NAM and hrrr forecasts.
 
Rain Cold said:
Looks like most models break the line apart as it gets into central sections of NC. Even the latest NAM is unimpressive. That's not to say that there won't be any wind reports, but I'm starting to wonder if we'll actually see an organized squall line moving through. The RAH AFD is impressive and the expansion of the Enhanced Risk area by SPC is noteworty, but virtually all of the models backed off of the intensity of the line through central NC. It reorganizes east of 95. If this continues, I wouldn't be surprised to see the SPC back off on the Enhanced Risk somewhat in the next Day 2 outlook.
Click to expand...

Yeah it seems to me most models are focusing the line getting going east of 95 and central NC is skipped as a result. Once we get fully in range of the HRRR we should get a better picture, it showed a pretty nasty line moving through Charlotte at the end of it's 6z run.
 
Webberweather53 said:
They’re almost definitely not going to back off the day 2 outlook just based on cam evolution at this stage, it would be more of a concern if we were actually on the day of the event and had actual obs to confirm or deny the NAM and hrrr forecasts.
Click to expand...
The most recent event is a pretty good example of this, even as the first line broke up overhead in the morning hours with additional prefrontal convection it seemed based on some of the CAMs esp the HRRR that we were done with severe weather, when in reality they did a piss poor job of picking up on the convection that developed near the cold front and moved thru central nc later that night. Severe weather forecasting is a completely different animal than winter weather. In a vast majority of cases you’re forecasting based on large scale conditions at hand and very general CAM evolution until several hours (or less) before the event.
 
Rain Cold said:
Looks like most models break the line apart as it gets into central sections of NC. Even the latest NAM is unimpressive. That's not to say that there won't be any wind reports, but I'm starting to wonder if we'll actually see an organized squall line moving through. The RAH AFD is impressive and the expansion of the Enhanced Risk area by SPC is noteworty, but virtually all of the models backed off of the intensity of the line through central NC. It reorganizes east of 95. If this continues, I wouldn't be surprised to see the SPC back off on the Enhanced Risk somewhat in the next Day 2 outlook.
Click to expand...

hmmmm, the NAM did the same exact thing with the last event, showed literally no QPF last Sunday and then the hrrr showed a line segment/QLCS making it into NC, and it actually was right, and I barely missed a tornado warning
 
Webberweather53 said:
They’re almost definitely not going to back off the day 2 outlook just based on cam evolution at this stage, it would be more of a concern if we were actually on the day of the event and had actual obs to confirm or deny the NAM and hrrr forecasts.
Click to expand...
I was looking at the globals too. I expect the mesoscale models to handle this better at this range, but virtually all models weaken the line substantially as they move through, reforming it after. Now, that doesn't mean they're correct, but they are in pretty good agreement right now. Extent and persistence of cloud cover will play a key role. We'll likely have to wait to see how that turns out. Things could go either way at this point, but if we continue to see models backing off, then I expect SPC will trim the outlook.
 
Myfrotho704_ said:
hmmmm, the NAM did the same exact thing with the last event, showed literally no QPF last Sunday and then the hrrr showed a line segment/QLCS making it into NC, and it actually was right, and I barely missed a tornado warning
Click to expand...
Yeah, I don't see there being nothing. I don't see there being no severe storms. I'm kind of skeptical about a widespread event through central NC, though.
 
Rain Cold said:
I was looking at the globals too. I expect the mesoscale models to handle this better at this range, but virtually all models weaken the line substantially as they move through, reforming it after. Now, that doesn't mean they're correct, but they are in pretty good agreement right now. Extent and persistence of cloud cover will play a key role. We'll likely have to wait to see how that turns out. Things could go either way at this point, but if we continue to see models backing off, then I expect SPC will trim the outlook.
Click to expand...

If the outlook is trimmed it wouldn't be today, at the earliest they'd do it tomorrow when we actually know what the conditions and convective evolution are like. At this stage you should really be mostly focused on the conditions in the CAMs here that lead to convective development & upstream verification today. So far I see no reason to be overly concerned about a forecast bust in either direction here. If you're basing a majority of your forecast on convective evolution on the CAMs more than several hours in advance, you're often going to get burned.
 
Lol it showed what appears to be one of those QLCS spinups right over my house, but has that type of situation throughout the line segment with bow echos and rotation at the inflow notches, i guess the storms is feeling some of those backing sfc winds helping out those inflow notches ? no doubt what the hrrr shows is nasty, I hope it’s wrong but it did decent at showing a the line with the last event 30 hours out, no model is perfect, hrrr can be to aggressive at times but it’s def something to watch 2406A386-28BE-4AB8-B026-EB23C76F60A3.jpeg
 
Webberweather53 said:
If the outlook is trimmed it wouldn't be today, at the earliest they'd do it tomorrow when we actually know what the conditions and convective evolution are like. At this stage you should really be mostly focused on the conditions in the CAMs here that lead to convective development & upstream verification today. So far I see no reason to be overly concerned about a forecast bust in either direction here. If you're basing a majority of your forecast on convective evolution on the CAMs more than several hours in advance, you're often going to get burned.
Click to expand...

I don't disagree. I certainly am not calling for a bust in either direction, but if I had to make a guess right now, I'd lean away from a widespread severe event in favor of a more typical spring scattering of storms, some of which become severe for a time. That's how this event looks to me. But, as you said, there are things that will matter that we just don't know the evolution of yet. It's wise to wait and see.
 
Rain Cold said:
I was looking at the globals too. I expect the mesoscale models to handle this better at this range, but virtually all models weaken the line substantially as they move through, reforming it after. Now, that doesn't mean they're correct, but they are in pretty good agreement right now. Extent and persistence of cloud cover will play a key role. We'll likely have to wait to see how that turns out. Things could go either way at this point, but if we continue to see models backing off, then I expect SPC will trim the outlook.
Click to expand...

If the line actually weakened as it entered central NC there are two primary perspective of looking at how it would affect the forecast. On the plus side, hopefully a weaker line well out ahead of the cold front in addition to pre-frontal convection eats up a lot of CAPE and limits further redevelopment later in the afternoon. On the other hand, the QLCS breaking up would encourage at least initially more isolated, discrete storms which actually elevates the tornado threat, or the QLCS is so weak that there's even less clouds/convection during the day so CAPE is even higher. Personally, I wouldn't be concerned either way yet about the line disintegrating or roaring thru based on what the precipitation output looks like on the models, again you should still really be mainly looking at the conditions that favor or discourage its evolution into central NC.

For sustaining a QLCS &/or large line segment, you need obviously a respectable amount of CAPE (500-1000 j/kg+), strong deep layer shear (preferably more than 30 kts) and lots of low-level SRH (100+ m2/s2 is a good general threshold), all 3 of those primary ingredients appear likely to be present tomorrow and in excess quantities at that. Not to mention there'll be a considerable amount of downdraft cape (DCAPE) thanks to drier air in the mid-levels which increases the threat for damaging straight line winds and may strengthen the low-level rear inflow jet associated w/ the QLCS, which effectively acts to maintain &/or intensity the line segment.

Going with an enhanced risk for most of central NC is likely the right call imo based on the aformentioned conditions at hand.


download - 2019-04-18T101245.100.png
 
Webberweather53 said:
If the line actually weakened as it entered central NC there are two primary perspective of looking at how it would affect the forecast. On the plus side, hopefully a weaker line well out ahead of the cold front in addition to pre-frontal convection eats up a lot of CAPE and limits further redevelopment later in the afternoon. On the other hand, the QLCS breaking up would encourage at least initially more isolated, discrete storms which actually elevates the tornado threat, or the QLCS is so weak that there's even less clouds/convection during the day so CAPE is even higher. Personally, I wouldn't be concerned either way yet about the line disintegrating or roaring thru based on what the precipitation output looks like on the models, again you should still really be mainly looking at the conditions that favor or discourage its evolution into central NC.

For sustaining a QLCS &/or large line segment, you need obviously a respectable amount of CAPE (500-1000 j/kg+), strong deep layer shear (preferably more than 30 kts) and lots of low-level SRH (100+ m2/s2 is a good general threshold), all 3 of those primary ingredients appear likely to be present tomorrow and in excess quantities at that. Not to mention there'll be a considerable amount of downdraft cape (DCAPE) thanks to drier air in the mid-levels which increases the threat for damaging straight line winds and may strengthen the low-level rear inflow jet associated w/ the QLCS, which effectively acts to maintain &/or intensity the line segment.

Going with an enhanced risk for most of central NC is likely the right call imo based on the aformentioned conditions at hand.


View attachment 19146
Click to expand...

Here's a forecasting area-averaged sounding over NWS RAH domain from the 12z 3km NAM. The 3km NAM arguably looks even better than the HRRR for maintaining the QLCS & line segment into central NC tomorrow w/ lots of surface-based & MUCAPE, strong low-level & deep layer shear, lots of 0-1 km SRH, in addition to plenty of DCAPE for enhancing downdrafts within the line. Given the strong-low level shear and 0-1 km SRH, there's obviously going to be a tornado threat from embedded, rain-wrapped mesovorts within the line.

download - 2019-04-18T102226.539.png
 
Webberweather53 said:
If the line actually weakened as it entered central NC there are two primary perspective of looking at how it would affect the forecast. On the plus side, hopefully a weaker line well out ahead of the cold front in addition to pre-frontal convection eats up a lot of CAPE and limits further redevelopment later in the afternoon. On the other hand, the QLCS breaking up would encourage at least initially more isolated, discrete storms which actually elevates the tornado threat, or the QLCS is so weak that there's even less clouds/convection during the day so CAPE is even higher. Personally, I wouldn't be concerned either way yet about the line disintegrating or roaring thru based on what the precipitation output looks like on the models, again you should still really be mainly looking at the conditions that favor or discourage its evolution into central NC.

For sustaining a QLCS &/or large line segment, you need obviously a respectable amount of CAPE (500-1000 j/kg+), strong deep layer shear (preferably more than 30 kts) and lots of low-level SRH (100+ m2/s2 is a good general threshold), all 3 of those primary ingredients appear likely to be present tomorrow and in excess quantities at that. Not to mention there'll be a considerable amount of downdraft cape (DCAPE) thanks to drier air in the mid-levels which increases the threat for damaging straight line winds and may strengthen the low-level rear inflow jet associated w/ the QLCS, which effectively acts to maintain &/or intensity the line segment.

Going with an enhanced risk for most of central NC is likely the right call imo based on the aformentioned conditions at hand.


View attachment 19146
Click to expand...

Dry air aloft is underrated, all the time in the summer when I’m supposed to get “garden variety T-storms” I end up getting a strong downburst becuase of the dry air aloft +high PWAT, high PWATs combined with dry air will create some water loading and negative bouyancy which creates such strong sinking in the downdraft, this combined with some of the wind associated with the LLvL jet, this is why I’m very concerned about wind damage if it was to make it here, it appears the higher PWAT will be more prevalent in eastern NC aswell
 
Myfrotho704_ said:
Dry air aloft is underrated, all the time in the summer when I’m supposed to get “garden variety T-storms” I end up getting a strong downburst becuase of the dry air aloft +high PWAT, high PWATs combined with dry air will create some water loading and negative bouyancy which creates such strong sinking in the downdraft, this combined with some of the wind associated with the LLvL jet, this is why I’m very concerned about wind damage if it was to make it here, it appears the higher PWAT will be more prevalent in eastern NC aswell
Click to expand...

Good points about the high PWATs and water loading (which are usually the biggest contributors to downdrafts). This definitely looks like a classic setup for a beefy QLCS pockmarked w/ rain-wrapped tornadoes.
 
Webberweather53 said:
The most recent event is a pretty good example of this, even as the first line broke up overhead in the morning hours with additional prefrontal convection it seemed based on some of the CAMs esp the HRRR that we were done with severe weather, when in reality they did a piss poor job of picking up on the convection that developed near the cold front and moved thru central nc later that night. Severe weather forecasting is a completely different animal than winter weather. In a vast majority of cases you’re forecasting based on large scale conditions at hand and very general CAM evolution until several hours (or less) before the event.
Click to expand...
Agreed the nam and hrrr basically had nothing or few broken showers sunday night.

The nams are probably reacting to that area of rain they develop early in the day across nc which weakens the subsequent development.

Sent from my SM-G955U using Tapatalk
 
Last edited:
From JP Dice for Alabama

Data is suggesting the higher tornado threat will be south of I-20 this evening combined with damaging straight-line winds. Elsewhere, we can expect a line of storms capable of producing winds over 60mph tracking from west to east beginning at around 5pm.

Sent from my Pixel 2 using Tapatalk
 
Webberweather53 said:
Even if there wasn't any convection tomorrow, boundary layer overturning alone would be able to produce 50+ mph (only slightly sub-severe) straight line surface winds given these absurd 850 hpa winds over the Carolinas.
View attachment 19148
Click to expand...

Eric, I noticed most models in soundings are showing winds in the 60kt range only 1,000 feet off the ground in portions of Eastern NC, some in the 65-70kt range. Apart from convection, is there a way to estimate how efficiently these winds could mix down to the surface in gusts? Here's an example sounding from the 3km NAM. Winds at 1,000 feet are right at 60kts but then at the surface they are sustained below 20kts. I would think in gusts 35-45mph could easily happen without the aid of any convection with a sounding like this?

1555601804060.png
 
And this sounding near the coast from the GFS shows 80kts at 1,000 feet above the ground with 40kts sustained at the surface.. Yikes.

1555602696439.png
 
You must log in or register to reply here.
Back
Top