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Severe WX Severe Threat 25 March 2021

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uhhhhh...no please
 
Weatherphreak said:
I know it’s just a model but a lot of famous tracks on that map. The Cullman, Marshall streak has been on every run I’ve seen. Hadn’t seen the Guin>Huntsville track till this one.
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my thoughts also. Pretty remarkable how those classic tracks show up on modeling (I am thinking of past events as well)
 
There are a couple of red flag type things that are starting to stand out to me while hyper-analyzing everything....

1. When you look at the 12-18z timeframe over north AL, as the more steady rain is shifting north through TN, the sfc winds are not disrupted by the ongoing cellular showers or storms. Low-level winds keep flowing right through. That tells me there is no cold pool reinforcement and that warm air/moisture advection is not interrupted.

2. Watch the HRRR as the supercells start in the afternoon and then mature. Think back to last week. Last week, the evolution was that a few clean supercells developed, and then storms immediately started forming everywhere and getting more and more widespread and more and more messy. However, with this system, it is the 180 degree polar opposite. As the supercells develop and mature in the environment, the weaker updrafts get weeded out and the projected radar screen gets cleaner and cleaner with time. This is a testament to the difference in the forcing/height falls/large scale ascent and the nature of the EML between the two events. In this event, what you have modeled is the geometry/nature of the large scale ascent, the EML, and the supercells themselves all working in tandem to weed out the smaller and weaker updrafts.
 
andyhb said:
View attachment 7409

That is an incredibly large region of ≥5 STP from the 15z SREF. For reference, the black contour is the mean, while the color shading represents probabilities of the STP reaching or exceeding that value.
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1616617098303.png
Here is your mean STP value. An area that large of 8 with nothing higher also tells me that they don't contour above 8 on there...
 
I find it very interesting (concerning) at how much higher the STP numbers are over western AL this week compared to last week. Don't get me wrong, they were noteworthy last week, with quite a few areas being above 5, but the numbers are maxed out significantly higher this week. Many counties in the 10+ range. Honestly, the STP map looks more similar to April 27, 2011, than it does to St. Patrick's Day imo.
 
Fred Gossage said:
Here is your mean STP value. An area that large of 8 with nothing higher also tells me that they don't contour above 8 on there...
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Yeah they max out at 8. The last time I saw anything like that there was... well I probably don't need to say it.
 
BMX's AFD for Thursday.

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Fred Gossage said:
There are a couple of red flag type things that are starting to stand out to me while hyper-analyzing everything....

1. When you look at the 12-18z timeframe over north AL, as the more steady rain is shifting north through TN, the sfc winds are not disrupted by the ongoing cellular showers or storms. Low-level winds keep flowing right through. That tells me there is no cold pool reinforcement and that warm air/moisture advection is not interrupted.

2. Watch the HRRR as the supercells start in the afternoon and then mature. Think back to last week. Last week, the evolution was that a few clean supercells developed, and then storms immediately started forming everywhere and getting more and more widespread and more and more messy. However, with this system, it is the 180 degree polar opposite. As the supercells develop and mature in the environment, the weaker updrafts get weeded out and the projected radar screen gets cleaner and cleaner with time. This is a testament to the difference in the forcing/height falls/large scale ascent and the nature of the EML between the two events. In this event, what you have modeled is the geometry/nature of the large scale ascent, the EML, and the supercells themselves all working in tandem to weed out the smaller and weaker updrafts.
Click to expand...
Fred, I see what your saying...supercells maturing and controlling the surrounding environment, a very scary thought.
 
Fred Gossage said:
There are a couple of red flag type things that are starting to stand out to me while hyper-analyzing everything....

... As the supercells develop and mature in the environment, the weaker updrafts get weeded out and the projected radar screen gets cleaner and cleaner with time...
Click to expand...

I was noticing that on the 18Z HRRR, as well. Reminds me of that day almost 10 years ago now (no, not calling for a repeat).

All things considered, tomorrow has a much more classic tornado outbreak look at the synoptic level than did last Wednesday. Honestly, I got caught up in the hype a little bit last Wednesday. I should have stuck with my gut and kept my amateur self-forecast capped at moderate risk/15 hatched. Granted this is with the benefit of hindsight, but there were a couple of strong potential limiting factors that stuck out (primarily the progged weakness of the LLJ until the last minute, and the influence of the "wedge"). Yes for tomorrow the evolution of prior warm sector convection ("junk") is a potential fly in the ointment, but so it was for last Wednesday (and even for that day), too. I'm not even seeing much if any veer-backing on any forecast soundings. I thought some of the forecast hodos going into last Wednesday were classic, but some were a little wonky. Not so this go-around.

The problem for SPC/local WFOs and local media now is, after all the nearly maxed out probabilities and very strong wording they used for last Wednesday, and for as bad as it was (and how close it was to being much worse); how to convey the message that tomorrow has the potential to be several orders of magnitude worse than that?
 
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Huntsville AFD
The warm front will be lifting through the area early Thursday
morning. The low-level jet is rather strong and expect the front
should not have as much issue pushing through the forecast area like
last week. Additionally, one of the main difference is the lack of
the wedge front to the east. Due to these two factors, expect the
warm front will push well to the north of the forecast area with
dewpoints climbing into the mid to upper 60s. The precipitation
associated with the warm front should push to the north of the area
late in the morning.

As the warm front exits to the north, this will be the key timeframe
to see how much destabilization happens ahead of the main round of
storms. The latest model guidance continues to tick up slightly on
the amount of destabilization. SBCAPE values of 1000-1500 J/Kg will
be realized Thursday afternoon with the warm front to the north. High
temperatures tomorrow will warm into the low to mid 70s with
dewpoints in the mid to upper 60s which will create a rather
volatile atmosphere. Another surge of the low-level jet is forecast
tomorrow afternoon and evening with 850 mb winds increasing to 50-60
kts. This low level shear will lead to 0-1 km SRH values of 250-400
m2/s2. Deep layer shear will be around 60-70 kts for 0-6 km bulk
shear. These values will be more than sufficient to support sustained
rotating updrafts. The surface low will also be deepening as it
tracks to the north of the forecast area. Supercells are supported
based of these parameters and shear vectors. Based on the shear
vectors, expect these storms will be moving quickly across the area
Thursday afternoon and evening. Shear vectors support speeds around
60 kts. All of these factors support all modes of severe weather
including tornadoes, damaging winds, large hail, and flooding. Based
on the latest guidance a few strong/long track tornadoes cannot be
ruled out. The main timeframe will be from roughly 1PM through 11PM
on Thursday. The entire forecast area is now in the moderate risk for
severe weather for Thursday. Please remain weather aware throughout
the day Thursday.
 
This set up parameter wise looks 5x worse than last week. It's going to be bad tomorrow, the only thing keeping it being from a top 5 event is if everything is messy like last week. HRRR is showing that being possible, but if the sun is out tomorrow for a little bit, pray and have a way of getting warnings.
 
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