Feb 28th - March 1st Severe Weather Outbreak

[andyhb]

Seems as if there will be some potential for severe wx into this sub-forum (mainly southern sections) come Tuesday/Wednesday with the large trough shifting eastward out of the west (D4 and D5 highlighted by SPC currently that I suspect will expand if the current look maintains itself). The extent of adequate CAPE (thanks to an EML, very cold 500 mb temperatures and decent moisture) and high deep layer shear is rather impressive for this time of year across the models.

The shift recently in guidance is to have a deeper, more consolidated system moving into the S Plains by Wednesday, as a low amplitude, lead northern stream vort slides ahead of it on Tuesday. The rather neutral height falls on Tuesday do give me some pause regarding convective initiation early on, but the region also appears to be in a rather favorable position regarding the upper jet for a fair amount of large scale ascent. Curious to also see how the low level response goes with this since areas that have more southerly BL flow could easily have a tornado threat as it stands now (even SSW surface winds on the GFS are leading to some sizable curved hodographs in the low levels).

Wednesday catches my eye with a rather rapidly deepening surface low (this may lead to more of an isallobaric response than is currently indicated and if it does, tornado potential really may become substantial) and a stronger LLJ than Tuesday, although the extent of the warm sector might not be quite as impressive as it is Tuesday.

[janetjanet998]

Was just about to post this but in the TN valley forum...these events will overlap several sub forums including this one

 

 

 

 

[andyhb]

1 minute ago, janetjanet998 said:

Was just about to post this but in the TN valley forum...these events will overlap several subfourms 

Yeah I am thinking this may require the main forum since it looks like at least three different regions may be impacted to some extent.

[Hoosier]

3 minutes ago, andyhb said:

Yeah I am thinking this may require the main forum since it looks like at least three different regions may be impacted to some extent.

Haven't looked at this one whatsoever. Generally do the main forum for something higher ceiling, not just widespread.  How bad does this look, potentially?

[andyhb]

6 minutes ago, Hoosier said:

Haven't looked at this one whatsoever. Generally do the main forum for something higher ceiling, not just widespread.  How bad does this look, potentially?

Well at 21z Tues to 00z Wed on the 12z GFS, there is 55-70 kts of 0-6 km shear juxtaposed with >1000 J/kg SBCAPE from the eastern half of OK all the way to Evansville (northern extent is almost to I-72 in IL). 500+ CAPE extent (enough to cause problems with that degree of shear) is greater still.

Then there's also Wednesday, which has an even higher range of deep layer shear with the trough ejecting, although the warm sector is likely to be a bit more confined.

[Indystorm]

Yeah, the Ohio Valley looks prime on GFS at this time for Wednesday with temps near 70, dews in low 60's, 1700 surface CAPE, lapse rates around 8, and helicity in 200's.  If the low slows down and strengthens areas up into central IL and IN could really get into play as Andy mentioned.

[Hoosier]

Quick look at the end of the 00z NAM has dews of 60+, CAPE over 2000, LI of -10 in parts of IL/IN.  That's pretty damn good for the first of March.

[andyhb]

Lovely 300 mile difference in surface low position at 18z Wed on a 6 hr dprog/dt between the 18z and 00z GFS. 

[Anti tornado]

Happened to see this on twitter. Impressive cape and sufficient srh and shear. Wind profiles leave a lot to be desired though at this point

[bjc0303]

7 minutes ago, Anti tornado said:

Happened to see this on twitter. Impressive cape and sufficient srh and shear. Wind profiles leave a lot to be desired though at this point

Well 1) that's 12z and 2) 70 knots deep shear + 300+ SRH in low levels = lot to be desired? huh?

[Hoosier]

That's a nice looking hodo, especially in the low levels.  Sure it could look better above 850 mb, but overall I'm just amazed to see that much CAPE at that latitude at 6/7 am.  

[Anti tornado]

3 minutes ago, Hoosier said:

That's a nice looking hodo, especially in the low levels.  Sure it could look better above 850 mb, but overall I'm just amazed to see that much CAPE at that latitude at 6/7 am.  

That's what I meant by the wind profile could be better/leaves some to be desired. When I saw the 2000+ cape at 12z I had to post it. That's impressive by itself for this time of year. 

 

[Hoosier]

Curious to see what SPC does on the day 3 outlook for Tuesday.  Some differences between the NAM and GFS but in either case, some threat would extend northward into the I-80 corridor.

[bjc0303]

1 minute ago, Hoosier said:

Curious to see what SPC does on the day 3 outlook for Tuesday.  Some differences between the NAM and GFS but in either case, some threat would extend northward into the I-80 corridor.

Very broad/large slight risk from southern plains east/northeast into ov...unless they decide to hold for better model clarity 

[Stebo]

1 hour ago, Anti tornado said:

That's what I meant by the wind profile could be better/leaves some to be desired. When I saw the 2000+ cape at 12z I had to post it. That's impressive by itself for this time of year. 

 

That is a great wind profile, not sure what you are talking about, the best shear is in the lowest km and there is speed shear above that which would help for tilting of the storm and venting at jet level. Not to mention the instability combined with it, I mean the EHI is around 5, that is damn good any time of the year.

[Hoosier]

2 hours ago, andyhb said:

Lovely 300 mile difference in surface low position at 18z Wed on a 6 hr dprog/dt between the 18z and 00z GFS. 

Looks like about a dozen of the GEFS members are slower than the op, which certainly is cause to throw up a caution flag.

[Stebo]

1 minute ago, Hoosier said:

Looks like about a dozen of the GEFS members are slower than the op, which certainly is cause to throw up a caution flag.

If the storm is slower that goes a big way for a better event.

[nwburbschaser]

4 minutes ago, Hoosier said:

Looks like about a dozen of the GEFS members are slower than the op, which certainly is cause to throw up a caution flag.

A few of those certainly point towards the Ohio Valley for Wednesday. 

[Anti tornado]

27 minutes ago, Stebo said:

That is a great wind profile, not sure what you are talking about, the best shear is in the lowest km and there is speed shear above that which would help for tilting of the storm and venting at jet level. Not to mention the instability combined with it, I mean the EHI is around 5, that is damn good any time of the year.

Critical angle is 43. My understanding is around 90 is ideal. 

 

Also, the surface to 6km wind barbs are not ideal. 

 

Additionally, after reviewing more soundings in the area, they are more veered at the surface. 

 

On a side note, won't that subsidence inversion coupled with fairly close temps and dew points lead to low level clouds? 

[Stebo]

1 minute ago, Anti tornado said:

Critical angle is 43. My understanding is around 90 is ideal. 

 

Also, the surface to 6km wind barbs are not ideal. 

 

Additionally, after reviewing more soundings in the area, they are more veered at the surface. 

 

On a side note, won't that subsidence inversion coupled with fairly close temps and dew points lead to low level clouds? 

90 is ideal, but how often do you get an ideal sounding. The winds are WSW at 850, which means you have 45 degrees of turning from surface to 850mb that is pretty good turning.  As for the inversion, it is a 12 sounding... that inversion would mix out as you get later in the day or the surface would warm so the inversion would be irrelevant.

[Anti tornado]

1 minute ago, Stebo said:

90 is ideal, but how often do you get an ideal sounding. The winds are WSW at 850, which means you have 45 degrees of turning from surface to 850mb that is pretty good turning.  As for the inversion, it is a 12 sounding... that inversion would mix out as you get later in the day or the surface would warm so the inversion would be irrelevant.

 

I guess I brought up the last part because it appears the models under did temps for Friday. Do morning inversions impact how models handle temps throughout the day or not really?

[Hoosier]

1 hour ago, Stebo said:

90 is ideal, but how often do you get an ideal sounding. The winds are WSW at 850, which means you have 45 degrees of turning from surface to 850mb that is pretty good turning.  As for the inversion, it is a 12 sounding... that inversion would mix out as you get later in the day or the surface would warm so the inversion would be irrelevant.

Yeah... we'd almost never get tornadoes/tornado outbreaks if we needed ideal/perfect conditions all the time.  I don't know about elsewhere but many tornado outbreaks in this region have occurred with good directional shear in the lowest km and very modest, or in some cases even close to nonexistent directional shear above that level.  I could rattle off a bunch of dates. Obviously when you get a situation where you have great directional/speed shear deep through the column and favorable synoptics, those are the ones you really pay close attention to.

As far as this Tuesday/Wednesday setup, just too much uncertainty in timing/evolution at this point. 

 

[csnavywx]

00Z Euro and GFS in pretty good agreement. That stout EML will likely cap warm sector development until large scale lift and the arrival of the cold front can erode it. Both models suggest right after dark on Tues evening, and the cap unzips along the front NE-SW. Very steep mid-level lapse rates, a stout CAPE profile across the hail growth zone (40-50% of total instability is right across the zone), and low WBZs (<10kft) should favor hail. Very strong speed shear in the CAPE zone should favor supers until it congeals into a line. Clouds and time of day will probably inhibit any tornado activity though.

[Hoosier]

8 minutes ago, csnavywx said:

00Z Euro and GFS in pretty good agreement. That stout EML will likely cap warm sector development until large scale lift and the arrival of the cold front can erode it. Both models suggest right after dark on Tues evening, and the cap unzips along the front NE-SW. Very steep mid-level lapse rates, a stout CAPE profile across the hail growth zone (40-50% of total instability is right across the zone), and low WBZs (<10kft) should favor hail. Very strong speed shear in the CAPE zone should favor supers until it congeals into a line. Clouds and time of day will probably inhibit any tornado activity though.

Do you think there's a chance that the steep lapse rates aloft and low level moisture advection still occurring after dark (at least per progs) could keep a surface based threat going even after dark?

[Chinook]

SPC day-3 outlook shows ENH for northern AR, southern MO. Slight risk extends from Texarkana AR to north of Indianapolis to Columbus. Here is a quote from the SPC's 2nd paragraph: "Strong shear profiles (60-70 kt effective shear) will result in a supercell-wind profile.  A wide array of possibilities are plausible at this time, including a risk for warm-air-advection storms developing during the late afternoon/evening over portions of AR and the MS Valley and yielding a tornado and hail risk."

[csnavywx]

43 minutes ago, Hoosier said:

Do you think there's a chance that the steep lapse rates aloft and low level moisture advection still occurring after dark (at least per progs) could keep a surface based threat going even after dark?

It could, but the moisture needs to be there to turn that critical EML base layer into a convectively unstable layer (near saturated underneath immediately underneath the capping layer). We know how dewpoints have been verifying lately, so don't hang your hat on that one just yet. Also, to prevent too much diurnal cooling, there needs to be a decent cloud canopy.

Regardless, a QLCS overturning that ridiculous EML could get pretty fun.

[janetjanet998]

maybe this should be moved to the main forum since it will eventually effect many subforms? all the way to the east coast?

 

edit: already 3 subforums discussing  this event now  (here,  western. TN valley)

 

looks like a moderate risk will be needed from southern MO/IL/IN back SSW into AR and TN if trends continue

 

 

[janetjanet998]

12z GFS stronger then 00z and seems to break CAP tuesday afternoon over AR area while NAM holds 

[Chambana]

Liking the looks of this. Especially for the extreme  southern portion of the sub. Glad to see severe season getting off to an early start. Last 2 years have been a drag. 

[Thundersnow12]

12 hours ago, Anti tornado said:

Happened to see this on twitter. Impressive cape and sufficient srh and shear. Wind profiles leave a lot to be desired though at this point

Huh? That's plenty of shear. Just look at the hodograph and a right mover would be almost moving ESE. Great directional and shear shear in the lowest few km.