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MattPetrulli

April 5-6 Severe Threat

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Storm Prediction Center issued a day 3 enhanced citing strong tornadoes and also have a day 4 risk out for the Mid Atlantic. Models certainly have some impressive parameters Wednesday with 2000-3000 j/kg of CAPE, some impressive shear with 60-70 knots, a 500 MB jet streak, a 40-50 knot LLJ, and discrete cell development with 65-70 degree dews. Some cons though is that we may face a morning MCS and maybe not the best backing of the winds. Still an impressive Dixie setup nonetheless and could be one of the bigger setups we've seen this year. NWS Birmingham also stats long tracked tornadoes possible in their AFD.

 

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This is the latest from James Spann regarding this Wednesday 

 

 

A very dynamic system with strong wind fields will impact the state with a fairly complex scenario.

WEDNESDAY MORNING: One batch of storms will blow through early Wednesday morning with a warm front lifting northward. These are most likely from 4 until 9 a.m… and some of these could be severe, with the main threat coming from hail and strong straight line winds, although an isolated tornado can’t be totally ruled out.

WEDNESDAY AFTERNOON: After a midday break in the rain, more storms will develop Wednesday afternoon into the evening hours. Instability values are forecast to soar, with surface based CAPE values nearing 3,000-4,000 j/kg by 4-5 p.m. With a strong low level jet and favorable shear profiles, some of these storms could be supercells with potential for large hail, damaging wind, and a few tornadoes. A strong tornado or two is certainly possible in the “enhanced risk” area.. and I would not be surprised if SPC upgrades this to a “moderate risk” (level 4 out of 5) in future outlooks based on forecast parameters.

But, understand the impact of the morning storms isn’t known, and there remains uncertainty in how the afternoon convection evolves. The bottom line is that Wednesday looks like an active severe weather day for much of Alabama, especially the eastern half of the state. Just pay attention to the blog discussions tomorrow and have a way of getting watches and warnings.

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Full AFD from Bmx detailing Wednesday's severe threats 

The associated cold front with the today`s system will become
diffuse across the northern Gulf Tuesday night as a strong upper
trough moves into the Plains. As the warm front moves inland,
elevated supercell thunderstorms appear likely Wednesday morning
with a potential for large hail and damaging winds. If any storms
become surface based during the morning, tornadoes would also be
possible. The evolution of this activity and additional convection
during the late morning/early afternoon remains in question and will
impact the nature of the severe weather threat for the afternoon and
evening. Several models are quite aggressive with warm sector
development through 18z Wednesday, which would cause the strongest
low-level shear to become displaced across our South and East. I am
not sold on this idea as of now for two reasons. An elevated mixed
layer should be present, which argues for limited thunderstorm
development. Also, the surface low should be well to our north
across the Ohio Valley at 18z Wednesday along with the synoptic warm
front. Arguing in favor of a contaminated warm sector is the
presence of a subtropical jet streak, but is not particularly
impressive. If the warm sector remains more free of convection, a
more substantial area-wide risk would develop. With all of that
said, the highest confidence in supercell storms capable of
producing long-track tornadoes, large hail, and damaging winds is
currently along and east of a line from Selma to Anniston. This
threat could expand westward with time and will hinge on early day
warm sector development.

 

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MHX NWS write up on it....

 

Wednesday through Thursday...Dangerous severe weather aprroach
possible during this period. Large scale upper trough
amplification is expected over the Eastern US Wed/Thur in
response to upstream flow and phasing jet streams. This will
result in powerful cyclogenesis across the central Appalachian
region to the lower Great Lakes through Thursday. Some timing
differences remain with exact placement of synoptic features
during this time frame, though it appears that a potentially
widespread severe weather outbreak could affect the region. The
aforementioned trough attains a strong negative tilt as it
swings through the Southeast US and as a result deep rich
moisture gets advected into the region in tandem with very
strong dynamics to support severe thunderstorms. Tremendous
height and pressure falls occur early Thursday as the sfc low
deepens to around 980MB to the north. 03/00Z GFS/CMC/ECM global
suite continue to indicate 850H flow of 50-70 kt aided by 110+
kt 300MB jet, and PW values AOA 1.5". Even if timing of the
severe threat is relegated to Wednesday night and early
Thursday, instability parameters are quite high due to the sharp
height falls yielding steep mid level lapse rates, and sfc TD`s
rising through the 60s overnight Wednesday. Hodographs are
quite troubling in that strong SRH values aoa 400 M2/S2 are fcst
by the NAM/ECMWF with low LCLs present. If all these
ingredients come together the threat for a few strong tornadoes
and strong damaging winds would be present.

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This could develop into a significant risk but it all depends on the low-level jet and the other ingredients coming into play all at the same time.  However, I will be on the watch for how the morning convection with the warm front will impact things, but we have seen situations where things can recover (see 04/27/11 for example) 

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Wednesday has all the makings of a significant severe weather outbreak across the Southeast, with an amplified/neutral-tilt 90kt upper-level trough and deepening surface low across the Ohio River Valley. Models are in good agreement dewpoints should progress into the upper 60s to near 70F as far north as central Alabama/Georgia by Wednesday afternoon. In addition, there will be a large area of steep lapse rates, a good elevated mixed layer, and unstable broad warm sector. Upper-end potential may be realized with this system if we can work two things, the first being the structure of the low-level jet (which looks quite weird on the NAM) and the second being the impact of the morning mesoscale convective system. Sometimes these MCSs ruin the day, other times it doesn't have a negating factor. Either way, I expect SPC to start with a Day 2 Moderate risk across central Alabama into southwestern Georgia.

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NAM 3k really has a high-end solution with the MCS coming through and rapid airmass recovery occurring. A line of discrete supercells forms in a very favorable airmass for tornadoes and begins an outbreak across TN/AL/GA with multiple long tracked UH tracks evident. Could certainly be big if the MCS doesn't ruin it.

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12 minutes ago, MattPetrulli said:

NAM 3k really has a high-end solution with the MCS coming through and rapid airmass recovery occurring. A line of discrete supercells forms in a very favorable airmass for tornadoes and begins an outbreak across TN/AL/GA with multiple long tracked UH tracks evident. Could certainly be big if the MCS doesn't ruin it.

Hey Matt.....haven't had a chance to check out the NAM.......roughly what time does it have the MCS pushing out of the eastern Alabama, north Georgia area?  Usually around here if the cloud cover and destabilization isn't off to a start by 11AM - 1PM, you can forget about any higher end severe event.  Hell, I didn't even hear a rumble of thunder today.  

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4 minutes ago, audioguy3107 said:

Hey Matt.....haven't had a chance to check out the NAM.......roughly what time does it have the MCS pushing out of the eastern Alabama, north Georgia area?  Usually around here if the cloud cover and destabilization isn't off to a start by 11AM - 1PM, you can forget about any higher end severe event.  Hell, I didn't even hear a rumble of thunder today.  

Cloud breaks begin in MS/AL by about 11-12. Supercells fire 4-5 PM according to NAM 3k. Will say 3k did preform very well yesterday, which really makes me think. 

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25 minutes ago, audioguy3107 said:

Hey Matt.....haven't had a chance to check out the NAM.......roughly what time does it have the MCS pushing out of the eastern Alabama, north Georgia area?  Usually around here if the cloud cover and destabilization isn't off to a start by 11AM - 1PM, you can forget about any higher end severe event.  Hell, I didn't even hear a rumble of thunder today.  

This looks to be an event focused on developing in East Alabama and West Georgia, so Metro Atlanta might have a significant risk of severe weather.  Remember usually when North Georgia faces severe weather is when the focus area is either East Alabama or along or near the AL/GA stateline.  I spent a huge portion of my life in East Alabama, and remember the majority of the tornado outbreaks that affected the Atlanta area begin right on top of the Anniston/Oxford/Gadsden/Talladega and/or Auburn/Opelika areas and moved east or northeast.

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This is not a good look for The Southern Piedmont and SC, especially given the timing. I'm growing more concerned for us late Wednesday into Thursday then I was for today. 

 

 

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latest update from the Alabama WX Weather Blog

 

James Spann | April 3, 2017 @ 9:17 pm

 

We will be watching new model data pouring in over the next few hours, with the highest interest in developments Wednesday, when severe thunderstorms are possible statewide.

No doubt the synoptic scale suggests it could be a big severe day, with a deep surface low northwest of Alabama supported by an upper trough with strong wind fields. As usual, the devil will be in the details.

We expect a batch of early morning storms as a warm front moves northward; generally in the 4-10 a.m. time frame. These, most likely, will be elevated, with the main risk coming from strong straight line winds and hail. But, this is the first week in April, and we will have to watch for any surprises. Should the morning storms be rooted in the boundary layer, there could be a tornado or two.

But, the main action should come during the afternoon and evening hours, generally between 2:00 p.m. and 7:00 p.m. The one thing that really sticks out is the very high surface based instability; some model guidance suggests surface based CAPE values could exceed 4,000 j/kg by mid-afternoon…

 

hires_cape_birmingham_52-600x450.jpg

 

 

This will create a “power keg” type atmosphere with high buoyancy with little in the way of a capping inversion. Storms should explode during the peak of the daytime heating process, and based on forecast parameters such as bulk shear, lapse rates, and the lack of convective inhibition, the storms are expected to become severe quickly, with all modes of severe weather possible, including tornadoes. And, maybe even a strong/violent tornado or two.

I would imagine the guys at SPC will put parts of the state under a “moderate risk” (4 out of 5) on their new outlook that comes out later tonight. One way or another, it looks like an active day with potentially dangerous storms.

PLACEMENT: Seems like the best combination of shear and instability will come over the eastern two-thirds of Alabama, but the entire state will see some risk of severe storms.

It is important to note we really don’t know how the morning storms will impact the state of the atmosphere, and exactly how the parameters will phase up during the afternoon. But, considering the time of the year and the setup, we all need to pay attention.

There is no need to be anxious, or overly concerned now, but just prepare.

CALL TO ACTION: Be sure you have a way of getting warnings; a NOAA Weather Radio is the baseline, and a good smart phone app is the other tier. Identify the safe place in your home, and be sure everyone knows where it is. And, in that safe place have helmets for everyone, along with hard sole shoes and preferably a portable airhorn in case you need help.

Be sure you have the ABC 33/40 app on your phone so you can watch our live severe weather coverage, if needed:

 

 

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7 minutes ago, weatherextreme said:

latest update from the Alabama WX Weather Blog

 

James Spann | April 3, 2017 @ 9:17 pm

 

We will be watching new model data pouring in over the next few hours, with the highest interest in developments Wednesday, when severe thunderstorms are possible statewide.

No doubt the synoptic scale suggests it could be a big severe day, with a deep surface low northwest of Alabama supported by an upper trough with strong wind fields. As usual, the devil will be in the details.

We expect a batch of early morning storms as a warm front moves northward; generally in the 4-10 a.m. time frame. These, most likely, will be elevated, with the main risk coming from strong straight line winds and hail. But, this is the first week in April, and we will have to watch for any surprises. Should the morning storms be rooted in the boundary layer, there could be a tornado or two.

But, the main action should come during the afternoon and evening hours, generally between 2:00 p.m. and 7:00 p.m. The one thing that really sticks out is the very high surface based instability; some model guidance suggests surface based CAPE values could exceed 4,000 j/kg by mid-afternoon…

 

hires_cape_birmingham_52-600x450.jpg

 

 

This will create a “power keg” type atmosphere with high buoyancy with little in the way of a capping inversion. Storms should explode during the peak of the daytime heating process, and based on forecast parameters such as bulk shear, lapse rates, and the lack of convective inhibition, the storms are expected to become severe quickly, with all modes of severe weather possible, including tornadoes. And, maybe even a strong/violent tornado or two.

I would imagine the guys at SPC will put parts of the state under a “moderate risk” (4 out of 5) on their new outlook that comes out later tonight. One way or another, it looks like an active day with potentially dangerous storms.

PLACEMENT: Seems like the best combination of shear and instability will come over the eastern two-thirds of Alabama, but the entire state will see some risk of severe storms.

It is important to note we really don’t know how the morning storms will impact the state of the atmosphere, and exactly how the parameters will phase up during the afternoon. But, considering the time of the year and the setup, we all need to pay attention.

There is no need to be anxious, or overly concerned now, but just prepare.

CALL TO ACTION: Be sure you have a way of getting warnings; a NOAA Weather Radio is the baseline, and a good smart phone app is the other tier. Identify the safe place in your home, and be sure everyone knows where it is. And, in that safe place have helmets for everyone, along with hard sole shoes and preferably a portable airhorn in case you need help.

Be sure you have the ABC 33/40 app on your phone so you can watch our live severe weather coverage, if needed:

 

 

Wow some strong wording from James Spann. 

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10 minutes ago, MattPetrulli said:

00z NAM guidance coming in less intense, but with still dangerous warm sector supercells forming. 

Could you please specify further what is less intense?

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2 minutes ago, kayman said:

Could you please specify further what is less intense?

Some areas don't recover as good as others projected in 18z. As a result, instability is down. LLJ is also weaker this run.

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Well the 00Z 4km NAM certainly is pretty terrifying.... uh yeah...Multple/waves of open warm sector discrete supercells within a very moist, highly unstable, and strongly sheared environment. 

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pretty classic looking setup for this region. Multiple corridors of supercell development likely, with discrete/semi-discrete mode expected given lack of linear forcing. Multiple CAMs back this up. Again - a pretty classic looking setup for widespread, significant severe east of the MS

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Bmx AFD with strong wording

Area Forecast Discussion
National Weather Service Birmingham AL
437 AM CDT Tue Apr 4 2017

.SHORT TERM...

...Severe weather outbreak possible Wednesday...

A stalled front to our south will begin to return northward
tonight as a classic 500 mb trough takes shape over the Plains. A
surface low should intensify and track from eastern Oklahoma
tonight toward the Ohio Valley on Wednesday, eventually putting
Alabama in the warm sector. Before that occurs, a warm front will
move inland and accelerate northward early Wednesday morning across
the forecast area. Scattered storms are expected to develop
around 4 AM as warm/moisture advection occurs near the warm
front. Additional storms could also form along a trailing
confluence band which may extend from central Alabama to the
southwest. With MLCAPE possibly as high as 2500 J/kg in the warm
sector and strong wind shear already in place through the entire
column, any surface-based storms could produce long-track
tornadoes. It is unclear how widespread this activity will be and
if storms will become more organized. This is an important
question we cannot answer at this time, but the morning activity
will greatly impact what happens later in the day.

One possible outcome is storms becoming organized and moving into
Georgia, focusing the low-level jet to the east with veering
surface winds to the west across Alabama. This could somewhat
reduce instability and shear and the overall threat for the
afternoon. A threat for tornadoes, very large hail and damaging
winds would still exist in this scenario. Several models are
buying into this idea, but with the presence of a elevated mixed
layer, it is possible they are too bullish with morning
thunderstorm development.

If the warm sector remains preserved, very strong instability and
shear would develop across much of the area, possibly leading to
an outbreak of long-track, destructive tornadoes trough 9 PM. The
westward extent of the afternoon threat is in question due to
timing of initiation, but the greatest chance for supercells would
probably occur east of a line from Birmingham to Selma. We should
have a better handle on this situation 24 hours from now.

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If the warm sector tomorrow is able to survive the overnight storms from the advancing warm front, I wouldn't be surprised if SPC goes with a high risk in their overnight day one outlook tonight/tomorrow.  This has real potential, the likes we haven't seen in quite a few years down here.  The wording from BHM is concerning and they are very good.

- Buck

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8 minutes ago, audioguy3107 said:

If the warm sector tomorrow is able to survive the overnight storms from the advancing warm front, I wouldn't be surprised if SPC goes with a high risk in their overnight day one outlook tonight/tomorrow.  This has real potential, the likes we haven't seen in quite a few years down here.  The wording from BHM is concerning and they are very good.

- Buck

I agree.  FFC seems to always take things too lightly and doesn't handle forecasting severe weather well at all.  I'm going to be monitoring what BMX, HUN, and James Spann take on the things as this system moves towards West and North Georgia.  I hope Metro Atlantans do not lull themselves into the false belief of never seeing a tornado because the conditions misses the area so often.

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