General Severe Weather

[ryan1234]

Well, much like I expected the enhanced area shifted east for tomorrow. I guess the question is how much destabilization occurs tomorrow. The tornado threat doesn't seem that high as of now, but I guess that is subject to change? A couple of you all mentioned the NAM as showing something pretty nasty. Today's threat across LA/MS looks downright ominous though. The ongoing question is, will that transpire east tomorrow?

[Solak]

Locally, things are juicing up. Currently 73/72.

RAH update:

14Z mesoanalysis and latest visible satellite imagery suggest the 
southern Piedmont into the Sandhills and southern Coastal Plain have 
become unstable with SBCAPE near or slightly above 2000 J/kg. 
Available bulk shear is sufficiently strong enough to support 
convection with bowing segments associated with strong/damaging 
winds. The presence of a low level boundary will enhance low level 
helicity, and with available instability, cannot rule out a storm or 
that displays supercellular characteristics, possibly producing 
large hail or a brief, weak tornado. This threat appears highest 
between 3 PM and 7 PM. 

[downeastnc]

Tor warned cell headed for Hickory.....couplet looked decent over Valdese is weaker now.....

[calculus1]

Tor warned cell headed for Hickory.....couplet looked decent over Valdese is weaker now.....

I'm at Lake Lure this weekend, but watched that radar signature closely. Fortunately, it weakened considerably before it passed over my house.

Sent from my moto e5 supra using Tapatalk

[Solak]

...Another severe threat Friday afternoon and night... 

Another large and potentially strong mid/upper low is forecast to 
move out of Texas into the lower Mississippi Valley by Thursday, 
then possibly cut off from the main jet stream over the Tennessee 
Valley region by Friday. The operational GFS at the current time 
appears to be an outlier solution (may be too far south) than the 
model consensus. Regardless, a deep fetch of subtropical air feed 
into the system from the western Atlantic and Gulf of Mexico 
potentially producing very heavy rainfall rates in convective bands 
that develop Friday into Friday night. In addition, shear again is 
expected to become significant Friday afternoon and evening 
increasing the severe threat (which may be comparable or higher than 
Sunday's event). We will carry likely POP Friday into Friday night 
for showers and thunderstorms. If the mid level circulation cuts 
off, then the cold upper levels combined with surface heating may 
continue to keep scattered showers and thunderstorms in the forecast 
Saturday. However, the highest severe threat, highest QPF, and POP 
will be on Friday and Friday night until the cold front passes. A 
drier NW flow is expected on the back side of the system by Saturday 
night into Sunday and Monday. 

[LithiaWx]

Solak,

Big time wind damage event looks pretty likely for North GA.  Looks like the whole forum is going to get some action this time.  I read WxSouth who is honking Tornadoes but NWS says QLCS with wind damage due to north to south orientation down here.  

[ryan1234]

Solak,
Big time wind damage event looks pretty likely for North GA.  Looks like the whole forum is going to get some action this time.  I read WxSouth who is honking Tornadoes but NWS says QLCS with wind damage due to north to south orientation down here.  

Yeah, wow. I just read what WX South said and he is making this system sound downright ominous. I guess we will wait and see.


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[shaggy]

Sounds like a windy day here in eastern nc friday even without the storms. 

A very strong LLJ (>60 kt around 925 mb)
will develop across the area as the stacked low passes inland,
riding northward along the Appalachian chain Friday and Friday
night. LLJ winds will readily mix to the surface during the day,
bringing strong/gusty winds, especially to coastal areas. A
wind advisory or warning may be needed for at least some of the
area. From a severe weather perspective: Instability is the
question as a moist prefrontal airmass will keep skies cloudy
and there is potential for showers ahead of the primary band of
convection, both inhibiting factors for the development of
surface based instability. Still, shear is strong enough to
justify a continued slight risk of severe weather from SPC,

[Solak]

The models continue to hone in on the heavy rain and severe 
(damaging wind and isolated tornado) threat for Friday into Friday 
evening for our region. 

Increasing gradient southerly winds of 20-30 mph with gusts to 40 
mph expected Friday.

The approaching mid/upper trough is forecast to become a full deep 
trough/closed upper low as it approaches from the west on Friday and 
Friday night. The main cold front is expected to push east through 
central NC Friday afternoon into Friday night. An narrow but strong 
plume of deep moisture will be tapped from the subtropics around 
Cuba and Greater Antilles up and along the cold front. Most likely 
record high precipitable water value anomalies in record territory 
for the middle of April (+3 to +4 standard deviations above normal), 
will lead to dew points in the upper 60s to lower 70s feeding into 
our region. This supply of moisture will lead to intense rainfall 
rates of 2-3 inches per hour with the heaviest showers/thunderstorms 
that will occur in bands as they move across the region Friday into 
Friday evening. QPF on the order of 1.5 to 2 inches can be expected 
with locally 2.5 inches storm totals (most areas will see the bursts 
of heavy rain for 3-6 hours as the bands move through).

Flash flooding will be possible given the saturated ground and 
recent high river levels. In addition, there is a chance of severe 
thunderstorms. The main threats will be damaging wind gusts as very 
strong winds aloft are forecast which can be tapped in the stronger 
and more intense cells or bands. Hail should be limited given the 
warm conveyor belt of subtropical moisture aloft. If there is any 
sun or breaks in the overcast (most likely in the Coastal Plain and 
eastward) then the damaging wind threat would increase given as the 
low level instability that can be tapped will become higher. Highs 
generally 70-75 west to 75-near 80 east. Gradient winds of 20 to 30 
mph will gust to 40 mph. 

The models suggest that a mid-level dry punch will arrive Friday 
evening and push the severe and flash flood threats to our east 
during the evening, leaving variably cloudy skies and scattered 
showers overnight. Lows in the upper 40s and 50s NW to E. 

[goldsborosnow]

The SPC has an enhanced risk for Eastern North Carolina on Friday.

[shaggy]

a bunch of years ago we had a "heavy shower warning" as a line of non-thunderstorm showers moved through and actually produced gusts to 70mph in greenville. I remember it because I was on my in to work when the warning came over the radio and we got nailed. It was winter time too though. The wording out of MHX seems to suggest heavy showers will still be enough to mix the LLJ down to the surface Friday evening. There is a typo where he says thursday instead of Friday.

Additionally, the primary band of prefrontal moisture
convergence will cross the area Thursday night and even though
instability will be somewhat limited, showers and thunderstorms
will bring the potential for damaging wind gusts as they readily
mix the very strong LLJ winds to the surface.

[hickory]

Its impressive to already have a enhanced risk for eastern NC for Friday. Considering it's still Wedsenday morning. Wouldn't be surprised if there is not a area of moderate risk come late torrommow or Friday morning.

[downeastnc]

SPC write up for Friday included this....

 

 ...Synopsis and Discussion...
   Deep upper trough extending along the MS Valley early Friday morning
   is expected to continue eastward, maturing into a well-formed
   mid-latitude cyclone centered over the southern Appalachians by the
   end of the period. Very strong flow aloft will exist throughout the
   base of the upper trough, with the strongest flow developing within
   its eastern periphery Friday afternoon and continuing into Saturday
   morning. 500-mb flow could exceed 100 kt, which is near record
   values across the Carolinas and into the mid-Atlantic based on SPC
   sounding climatology. In contrast to these impressive dynamics,
   overall thermodynamic environment will be marginal. Given that ample
   low-level moisture will be in place (i.e. dewpoints in the mid 60s
   to low 70s and 100-mb mean mixing ratios over 12 g/kg), the modest
   instability is largely a result of warm temperatures aloft and
   consequent poor lapse rates. 

[ryan1234]

Its impressive to already have a enhanced risk for eastern NC for Friday. Considering it's still Wedsenday morning. Wouldn't be surprised if there is not a area of moderate risk come late torrommow or Friday morning.

I’d be surprised to a moderate risk, given instability won’t be great. It’s definitely a high shear, low cape setup. Although WX South thinks otherwise. We shall see I guess.


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[jjwxman]

For the Carolinas: I don't think we'll see a Moderate Risk. (but what do i know )  There are few things that will plague this forecast. 1st. The influx of tropical moisture will likely cause a warm layer around the 700-500mb level, this will weaken the mid level lapse rates. 2nd. The whole column looks very tropical, there will likely be a lot of cloud cover so CAPE will be limited.  3rd.  PW values will likely be at record territory for this time of year, and with the slow progress of the system west to east, flooding will probably be the forefront of this event from training storms. I wouldn't be surprised to see some 2-4" rain totals in some areas.  4th. If we do see some sun and decent destabilization then this could turn out to be a significant severe weather event, particular for damaging winds, the hodographs are more elongated than curved, so the tornado threat should remain isolated in nature unless we get more backing from SE surface winds.  A lot to decipher over the coming days.  

[Cold Rain]

1 hour ago, jjwxman said:

For the Carolinas: I don't think we'll see a Moderate Risk. (but what do i know )  There are few things that will plague this forecast. 1st. The influx of tropical moisture will likely cause a warm layer around the 700-500mb level, this will weaken the mid level lapse rates. 2nd. The whole column looks very tropical, there will likely be a lot of cloud cover so CAPE will be limited.  3rd.  PW values will likely be at record territory for this time of year, and with the slow progress of the system west to east, flooding will probably be the forefront of this event from training storms. I wouldn't be surprised to see some 2-4" rain totals in some areas.  4th. If we do see some sun and decent destabilization then this could turn out to be a significant severe weather event, particular for damaging winds, the hodographs are more elongated than curved, so the tornado threat should remain isolated in nature unless we get more backing from SE surface winds.  A lot to decipher over the coming days.  

Strongly agree with all of this.

[jjwxman]

45 minutes ago, Cold Rain said:

Strongly agree with all of this.

But the 12z NAM suite just made a case for the moderate risk...  Geez look at those backing SE Surface winds.  Increased surface cape as well, slower with the system.

[ryan1234]

But the 12z NAM suite just made a case for the moderate risk...  Geez look at those backing SE Surface winds.  Increased surface cape as well, slower with the system.

I just saw that as well. Some of those cells entering the southern piedmont look to be discrete as well. Not a good look. Does anyone have any insight as far as Robert(WX South) does with severe weather? He called this potentially historic.


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[CAD_Wedge_NC]

33 minutes ago, ryan1234 said:

 

I just saw that as well. Some of those cells entering the southern piedmont look to be discrete as well. Not a good look. Does anyone have any insight as far as Robert(WX South) does with severe weather? He called this potentially historic.


.

 

Robert was our go-to Met on this board for many years. He is excellent with winter weather in our part of the world. However, I really wasn't into severe weather back then. So, I can't comment on his severe forecast, but I would not bet against it right now.

[jjwxman]

The word "Historic" should only be used during or after an event IMO. 4/16/11 was historic. 

[Moultrie]

Love all the insight y’all have here. I’m the definition of uneducated when it comes to weather but I love following this forum. Appreciate yalls  posts greatly. 

[downeastnc]

This setup has tons of potential to be epic or to bust....if we manage to get breaks in the clouds and can get any kind of real instability like the NAM has, plus some kind of surface low reflection over the upstate of SC to back the winds then Friday could be epic.......it could also stay cloudy all day and be a typical skinny cape high shear squall line that gives sporadic bowing segments with winds 60-70 mph.....but overall a meh day.

[jjwxman]

Regardless, I'm not sure if I've ever seen wind speeds this high above the surface over NC.  Incredible.  Lots of potential, but like @downeastnc said the bust potential is high as well.

[Cold Rain]

48 minutes ago, jjwxman said:

Regardless, I'm not sure if I've ever seen wind speeds this high above the surface over NC.  Incredible.  Lots of potential, but like @downeastnc said the bust potential is high as well.

The winds upstairs are going to be at the upper end of what we usually see around here.  RE: the NAM, I do not trust its depictions of CAPE or meso lows and such right now.  It always looks scary severe weather-wise.  I won't say there's zero tornado risk because we just don't know yet.  At this point, what we do know is that there are some things look likely and some things look possible.

It looks likely that instability will be limited, due to an elevated warm layer and a largely overcast sky.  It looks likely that there will be a lot of wind energy aloft that can be easily tapped.  It looks likely that there will be a lot of rain, and the soil will be easily saturated.  It looks likely that flooding will be a concern.  It looks likely that even if winds remain below severe limits in most areas, downed trees would still be a concern, due to the aforementioned soil conditions.

It is possible that instability will be higher if breaks in the cloud cover occur (hard to tell at this lead).  It is possible that a meso-low forms, backing the low level winds and increasing the tornado threat, at least for eastern areas.  It is possible that convection earlier in the day reduces instability by the time the main forcing comes through, thus reducing the wind threat.

The main take-aways for me right now are that the potential is there for widespread wind damage reports, resulting from a squall line.  There is not yet enough clarity or broad support to justify anything higher than an Enhanced Risk at this point, IMO.  I certainly wouldn't be using the word "historic" yet.  It is possible that things could change for the worse.  But that is not the most likely scenario, based on the data available right now.

[downeastnc]

RAH AFD this afternoon highlights the main points rather well.......

The beginning of the long term continues to be the time of interest
as a maturing mid-level cyclone moves over the Ohio Valley. Friday
morning a low level stratus deck will likely be in place which will
help to create a differential heating boundary across the CWA. The
NAM at this time also indicates a weak confluence boundary over the
CWA. These multiple mesoscale boundaries will likely play a key role
in how Friday develops. Friday afternoon PWATs will continue to rise
and approach 1.7" as strong low level southerly flow helps to advect
moisture into central North Carolina. These type of PWATs would be a
monthly record. A surface low will then form across western North
Carolina Friday afternoon into evening and pinwheel northeast as the
mid-level low takes on a negative tilt. SFC to 3 km shear values are
again extremely impressive with values around 40 kts. Instability
with the system remains in question. MU CAPE values on the GFS
are in general less than 1000 J/kg while MU CAPE values on the NAM
are more around 2000 J/kg. The main threats with this system will be
damaging wind gusts (owing to the extremely strong low level flow),
heavy rainfall, and isolated tornadoes. SPC currently has the area
outlooked in a Day 3 enhanced.
 

[downeastnc]

18Z NAM is just a wee bit concerning.........seriously some of the most insane sounding for NC you will ever see....also this line of semi discrete cells over central eastern NC would be exactly the kind of stuff we don't wanna see.....then the line its self is gonna be crazy efficient at getting those 70-80 knt winds just off the surface down.....could be a heck of a event if the NAM is right.

 

 

[ryan1234]

18Z NAM is just a wee bit concerning.........seriously some of the most insane sounding for NC you will ever see....also this line of semi discrete cells over central eastern NC would be exactly the kind of stuff we don't wanna see.....then the line its self is gonna be crazy efficient at getting those 70-80 knt winds just off the surface down.....could be a heck of a event if the NAM is right.

 
 

That’s definitely not something you want to see. The NAM may very well be onto something. If so it’s time to batten down the hatches and prepare some significant weather. GSP had a pretty good discussion and even mentioned they wouldn’t be surprised seeing the enhanced risk spread westward.


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[shaggy]

1 hour ago, ryan1234 said:

 

 

That’s definitely not something you want to see. The NAM may very well be onto something. If so it’s time to batten down the hatches and prepare some significant weather. GSP had a pretty good discussion and even mentioned they wouldn’t be surprised seeing the enhanced risk spread westward.


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The nam was pretty bullish on a big set of supercells last weekend developing ahead of the front and it was worse case and it didnt happen. When I see such extreme solutions I always suspect it as being bogus. 

[ryan1234]

2 hours ago, shaggy said:

The nam was pretty bullish on a big set of supercells last weekend developing ahead of the front and it was worse case and it didnt happen. When I see such extreme solutions I always suspect it as being bogus. 

I couldn't agree more! Last weekend was a huge bust for my area. It's too bad too. I know models aren't perfect, but when severe weather bust like that, it causes people to lose faith and interest in severe weather. I just feel like when the time comes for another outbreak, people are going to be unprepared. Heck, the Joplin tornado occurred on a Moderate risk day. I really wish people would take the time to educate themselves on tornadoes in the Carolina's. Brad P. posted an awesome and very informative video on tornadoes in our region/state. 

[downeastnc]

5 hours ago, ryan1234 said:

I couldn't agree more! Last weekend was a huge bust for my area. It's too bad too. I know models aren't perfect, but when severe weather bust like that, it causes people to lose faith and interest in severe weather. I just feel like when the time comes for another outbreak, people are going to be unprepared. Heck, the Joplin tornado occurred on a Moderate risk day. I really wish people would take the time to educate themselves on tornadoes in the Carolina's. Brad P. posted an awesome and very informative video on tornadoes in our region/state. 

There are a ton of reasons to not buy in totally to the NAM, but even if its over done by half thats still a rough day.....really I think its a safe bet that at the minimum we see several broken line segments all of which will produce severe criteria wind gust over a fairly large area, it should not be hard to get some impressive winds to the surface given the wind field aloft......the real question is do we get enough instability to fire those semi discrete supes with a leeside surface low.....