Severe Potential March 2nd/3rd: OV, TN Valley, Mid-South, Deep South, Mid-Atlantic, Carolinas

[beneficii]

If someone offers a different insight to a process why can't you take it and learn from it instead of trying to rip it a part? And justify to yourselves it's wrong just because it isn't something that you learned? Why don't you take it, keep it in the back of your mind and watch it play out or analysis it after the event. NONE of you care about post analysis...it even showed when WXSTN74 posted he post analysis of why the storm under performed last week in Michigan and no one even commented on it or read it for that matter. You were all on to the next storm a week away. You can learn alot from going back over models and seeing what they did and didn't do wrong and what they were proging at different levels.

When you initially posted, I didn't have a problem with what you were saying. There was, however, something wrong with your approach, even if I can't quite pinpoint it. It seemed like you came in with a confrontantional manner from the start.

[QVectorman]

you mean like the cold front/dry line that will be blasting through the area

Yes, BUT the mid/upper level forcing is acting opposite of the sfc trigger. It's not a hard concept. What's hard to grasps here, you have a sfc trigger creating +lift. but the mid/upper level dynamics are producing -lift. What's the result...counter acting motion that results in crap convection. Verses great convection and strong updrafts when you have sfc. lift teaming up with +vv's

[baroclinic_instability]

Ok this is getting a little old. Please keep the disco on topic to the event, not on whether models show good UVV's or not. Personally could care less what the models are showing for UVVs since DMC is going to be parameterized and is dependent upon many things.

[baroclinic_instability]

If someone offers a different insight to a process why can't you take it and learn from it instead of trying to rip it a part? And justify to yourselves it's wrong just because it isn't something that you learned? Why don't you take it, keep it in the back of your mind and watch it play out or analysis it after the event. NONE of you care about post analysis...it even showed when WXSTN74 posted he post analysis of why the storm under performed last week in Michigan and no one even commented on it or read it for that matter. You were all on to the next storm a week away. You can learn alot from going back over models and seeing what they did and didn't do wrong and what they were proging at different levels.

Analysis is good, very good, but take a deep breath and calm down. You are definitely becoming confrontational now. I don't think anyone here wants a massive outbreak, but I do agree sometimes hype is overdone. I like your approach of looking for ways things may not all work out, but you are doing it all wrong with your posting style.

[PSUBlizzicane2007]

Yes, BUT the mid/upper level forcing is acting opposite of the sfc trigger. It's not a hard concept. What's hard to grasps here, you have a sfc trigger creating +lift. but the mid/upper level dynamics are producing -lift. What's the result...counter acting motion that results in crap convection. Verses great convection and strong updrafts when you have sfc. lift teaming up with +vv's

You know, you need to review the 18Z NAM anyways. After further review, vv are positive in the same location in C KY at 850, 700, and 500mb... so I'm not really sure anymore what the point of this discussion is.

[QVectorman]

Analysis is good, very good, but take a deep breath and calm down. You are definitely becoming confrontational now. I don't think anyone here wants a massive outbreak, but I do agree sometimes hype is overdone. I like your approach of looking for ways things may not all work out, but you are doing it all wrong with your posting style.

I apologize if my tone came off confrontation. Not trying to be rude. As I stated, my original intent was to share my ideas on the forecast and the reasons behind those ideas and I kept being critiqued saying my process is wrong/flawed. My apologizes though.

[QVectorman]

You know, you need to review the 18Z NAM anyways. After further review, vv are positive in the same location in C KY at 850, 700, and 500mb... so I'm not really sure anymore what the point of this discussion is.

Agreed, I said things would change, from run to run, they will change up to the event.

[baroclinic_instability]

These off hour runs the last two days keep going ballistic only to be "reeled" back in with the synoptic runs. GFS/NAM/RGEM at 18Z all went crazy. RGEM bombs the low 972 by 06Z on the third. Synoptic differences make notable potential difference on severe mode as well as placement of fronts. Guidance having sensitivity issues...likely to the upper level wave pattern and the backside wave ejecting the ROckies. Timing of rapid cyclogenesis/feedback makes huge differences on overall cyclone evolution.

[PatrickSumner]

These off hour runs the last two days keep going ballistic only to be "reeled" back in with the synoptic runs. GFS/NAM/RGEM at 18Z all went crazy. RGEM bombs the low 972 by 06Z on the third. Synoptic differences make notable potential difference on severe mode.

I thought the 18Z runs were just as good as the others now...

[CUmet]

Ok this is getting a little old. Please keep the disco on topic to the event, not on whether models show good UVV's or not. Personally could care less what the models are showing for UVVs since DMC is going to be parameterized and is dependent upon many things.

This. All this talk of UVV gradients in the model is meaningless when it doesn't have explicit convection. As far as I understand it, you need UVV gradients for vorticity generation and tornadogenesis, true, but this occurs at a scale smaller than is being resolved by the global models that are being referenced here.

[baroclinic_instability]

I thought the 18Z runs were just as good as the others now...

I think they are useful tools in the forecast process...especially for shorter range events. They can also be useful in dprog/dt analysis, etc. From a global modeling standpoint longer range, I think they lose their effectiveness. Even then, the 00/12Z guidance still has a huge advantage of global raob data ingested into the analysis.

[QVectorman]

This. All this talk of UVV gradients in the model is meaningless when it doesn't have explicit convection. As far as I understand it, you need UVV gradients for vorticity generation and tornadogenesis, true, but this occurs at a scale smaller than is being resolved by the global models that are being referenced here.

You need it on the large scale in order to enhance the small scale. But again...taken out of context. I am looking at vv on a synoptic/ dynamic scale to gauge the potential strength of up drafts that do form over the region. Which would there by produce stronger storms in general.

That was also my other point is is that if convection is not showing on the radar simulated or q p f forecast and there is,-vv being shown over the region its most likely because the mid and upper level forcings are not there due to a cold air advection NVA or whatever

[AtticaFanatica]

The only thing that's bothered me about this conversation is: it's "tornadogenesis" and "updraft", one word, at least in the lit.

[QVectorman]

The only thing that's bothered me about this conversation is: it's "tornadogenesis" and "updraft", one word, at least in the lit.

first 1 is my fault second 1 sorry posting from the phone and did not feel like trying to make my phone take up draft as one word when I'm typing fast

[Calderon]

Umm, wow. OHX/BNA hardly ever goes with wording this strong, they're a well-known conservative office.

AREA FORECAST DISCUSSION

NATIONAL WEATHER SERVICE NASHVILLE TN

329 PM CST THU MAR 1 2012

.DISCUSSION...A BIG SEVERE WX OUTBREAK IS EXPECTED FOR MID TN

FRIDAY. STRONG LONG TRACK TORNADOES...DAMAGING WINDS AND LARGE

HAIL ARE ALL POSSIBLE. SPC CONTINUES TO POST A MODERATE RISK FOR

SEVERE WEATHER OVER THE MID STATE. THIS EVENT LOOKS MORE

WIDESPREAD AND SUBSTANTIAL THAN THE SEVERE THREAT WE HAD

YESTERDAY...PROBABLY THE BIGGEST OUTBREAK OF TORNADOES SINCE

APRIL 27, 2011. THIS EVENT COULD BE ONE OF THE GREATER IMPACT

EVENTS IN THE PAST FEW YEARS. THE PUBLIC SHOULD BE STRONGLY ADVISED

TO TAKE THIS THREAT VERY SERIOUSLY.

[Superstorm93]

Umm, wow. OHX/BNA hardly ever goes with wording this strong, they're a well-known conservative office.

AREA FORECAST DISCUSSION

NATIONAL WEATHER SERVICE NASHVILLE TN

329 PM CST THU MAR 1 2012

.DISCUSSION

Full Disco

DISCUSSION...A BIG SEVERE WX OUTBREAK IS EXPECTED FOR MID TN

FRIDAY. STRONG LONG TRACK TORNADOES...DAMAGING WINDS AND LARGE

HAIL ARE ALL POSSIBLE. SPC CONTINUES TO POST A MODERATE RISK FOR

SEVERE WEATHER OVER THE MID STATE. THIS EVENT LOOKS MORE

WIDESPREAD AND SUBSTANTIAL THAN THE SEVERE THREAT WE HAD

YESTERDAY...PROBABLY THE BIGGEST OUTBREAK OF TORNADOES SINCE

APRIL 27, 2011. THIS EVENT COULD BE ONE OF THE GREATER IMPACT

EVENTS IN THE PAST FEW YEARS. THE PUBLIC SHOULD BE STRONGLY ADVISED

TO TAKE THIS THREAT VERY SERIOUSLY.

FOR TONIGHT...CLEAR SKIES EARLY WITH HIGH PRESSURE. DEEP MOISTURE

WILL SURGE INTO THE AREA AFTER MIDNIGHT AS A WARM FRONT LIFTS

NORTHWARD AND LOW PRESSURE DEEPENS OVER THE MID MS VALLEY. A

CHANCE FOR THUNDERSTORMS WILL DEVELOP OVER MID TN LATE IN THE

NIGHT...AND SOME MAY PRODUCE HAIL. A FEW REPORTS OF MARGINALLY

SEVERE HAIL ARE NOT OUT OF THE QUESTION AS A 40-50KT LLJ HELPS

DESTABILIZE THE MID LAYER.

ON FRIDAY...LOW PRESSURE WILL DEEPEN AS IT MOVES FROM THE MID MS

VALLEY TO THE GREAT LAKES. HEIGHTS WILL FALL AS A BROAD DEEP

TROUGH APPROACHES. A COLD FRONT WILL MOVE TO NW MID TN BY 00Z

SAT. WE EXPECT EARLY MORNING THUNDERSTORMS TO LIFT TO THE

NORTHEAST WITH THE WARM FRONT. THEN PARTLY SUNNY...WARM AND BREEZY

CONDITIONS WILL DEVELOP. TEMPERATURES WILL WARM WELL INTO THE 70S

AND PERHAPS LOWER 80S. THE BNA RECORD FOR MARCH 2ND IS 80 FROM

1951. FORECAST SOUNDINGS SHOW VERY IMPRESSIVE PARAMETERS WITH STRONG

WINDS AND INSTABILITY. NEW DEVELOPMENT OF STORMS COULD BEGIN BY

NOON...AND WHEN STORMS GET GOING...RAPID INTENSIFICATION WILL

OCCUR. THE EXPECTED TIMES OF HIGHEST IMPACT SEVERE WEATHER ARE

NOON TO 4 PM NEAR THE TN RIVER...2 PM TO 6 PM FOR BNA AND THE I 65

CORRIDOR...AND 3 PM TO 8 PM ON THE CUMBERLAND PLATEAU.

SEVERE WEATHER POTENTIAL WILL LINGER INTO THE EARLY EVENING OVER

THE EAST HALF...BUT THE COLD FRONT SHOULD BE PUSHING WELL EAST OF

OUR AREA BY MIDNIGHT.

[dtk]

I think they are useful tools in the forecast process...especially for shorter range events. They can also be useful in dprog/dt analysis, etc. From a global modeling standpoint longer range, I think they lose their effectiveness. Even then, the 00/12Z guidance still has a huge advantage of global raob data ingested into the analysis.

Not this again...In terms of the medium range global modeling, I don't necessarily agree with what you're saying. There is a thread on this in the Met101 subforum.

[tmagan]

18Z RGEM

[baroclinic_instability]

Not this again...In terms of the medium range global modeling, I don't necessarily agree with what you're saying. There is a thread on this in the Met101 subforum.

You are the data assimilation man, so I am not going to disagree with you, but from a user stand point, the off hour guidance seems to be more prone to odd "blips"/weird runs on occasion, more often than the synoptic guidance, even if scores look identical. That is just my standpoint after using this guidance daily as forecasting tools, and I try my best to remain objective when making criticisms/comments on the guidance. I should note these seem to relatively uncommon as a whole, and I do find off-hour guidance quite useful, especially with intense systems in the short range as they can fill a nice "gap" regarding dprog/dt trends in significant features of a storm--especially feedback scenarios.

[Superstorm93]

18z RGEM anyone?

[LouWX]

Typically don't post here much, but I did want to share a few thoughts (Louisville centric post, btw):

LL Jet that passes through around 1PM as the warm air just arrives as well as the moisture. If some storms can develop on this leading edge of the jet streak passing by, we could see severe weather develop early in the afternoon and race northeastward.

CAP develops in the afternoon according to latest NAM sounding at 21Z, which could put a lid on things.

Front arrives in the 21Z to 0Z time frame. The jet I mentioned will be moving over and perhaps northeast of us by then, which may promote divergence in the low layers and a decreased storm threat. Plus, with storms maybe popping up to our south, a potential for our storms to get disrupted exists.

Despite that, I still am impressed with and fell that the sharpness of the cold front may be able to overcome the above and keep a thin line of convection on the boundary going, actually quite similar to Hi-Res WRF solution 18Z run.

I said this earlier today on another outlet...

I don’t think it is wise right now for a meteorologist in this part of the world to say any thing “absolute” about this system… saying things like we will see tornadoes -or- severe weather will occur only serves to panic folks… and I really think it is critical to reserve these comments for when we absolutely know and feel that storms are going to happen.

I find myself somewhere in the middle of the extensive conversation in this thread today about the storm setup tomorrow. I am impressed with the indices and numbers on paper, but seem to be finding myself looking at this thing just having a gut feeling it may have bust written on it - it just seems all a little disjointed and that new 18Z NAM cap certainly is not helping the situation become any clearer.

I welcome your thoughts... on my comments above. Yep, it's a good looking setup on paper. But POTENTIAL energy does not always translate into an outbreak, so I'm keeping that in mind while also realizing that if storms decide to get going, yeah --watch out!

[Superstorm93]

Exactly.

Potential means nothing until it is actually utilized

[Hoosier]

18Z RGEM

Where did you get those maps?

[QVectorman]

Typically don't post here much, but I did want to share a few thoughts (Louisville centric post, btw):

LL Jet that passes through around 1PM as the warm air just arrives as well as the moisture. If some storms can develop on this leading edge of the jet streak passing by, we could see severe weather develop early in the afternoon and race northeastward.

CAP develops in the afternoon according to latest NAM sounding at 21Z, which could put a lid on things.

Front arrives in the 21Z to 0Z time frame. The jet I mentioned will be moving over and perhaps northeast of us by then, which may promote divergence in the low layers and a decreased storm threat. Plus, with storms maybe popping up to our south, a potential for our storms to get disrupted exists.

Despite that, I still am impressed with and fell that the sharpness of the cold front may be able to overcome the above and keep a thin line of convection on the boundary going, actually quite similar to Hi-Res WRF solution 18Z run.

I said this earlier today on another outlet...

I don’t think it is wise right now for a meteorologist in this part of the world to say any thing “absolute” about this system… saying things like we will see tornadoes -or- severe weather will occur only serves to panic folks… and I really think it is critical to reserve these comments for when we absolutely know and feel that storms are going to happen.

I find myself somewhere in the middle of the extensive conversation in this thread today about the storm setup tomorrow. I am impressed with the indices and numbers on paper, but seem to be finding myself looking at this thing just having a gut feeling it may have bust written on it - it just seems all a little disjointed and that new 18Z NAM cap certainly is not helping the situation become any clearer.

I welcome your thoughts... on my comments above. Yep, it's a good looking setup on paper. But POTENTIAL energy does not always translate into an outbreak, so I'm keeping that in mind while also realizing that if storms decide to get going, yeah --watch out!

Agreed! Thank you. Much more eloquent conveying your thoughts than I was but same none the less

[CUmet]

You need it on the large scale in order to enhance the small scale. But again...taken out of context. I am looking at vv on a synoptic/ dynamic scale to gauge the potential strength of up drafts that do form over the region. Which would there by produce stronger storms in general.

That was also my other point is is that if convection is not showing on the radar simulated or q p f forecast and there is,-vv being shown over the region its most likely because the mid and upper level forcings are not there due to a cold air advection NVA or whatever

But that's the thing...you can't really do this. The updraft associated with a supercell does not scale with the magnitude of the synoptic scale vertical velocity (at any vertical level) in the real world. You can't even do this in the global model world because the model resolution is too coarse to resolve convection, so the model's vv may not necessarily correspond with it trying to show convective vv.

This is not to say that the model's vertical velocity output is completely useless in convective forecasting, as there are things you can infer from it. But one has to be very cautious and keep the above points in mind.

For what it's worth, I don't think this will be a high risk type of tornado outbreak either, but my skepticism has very little to do with the synoptic scale or model output vertical velocities.

[QVectorman]

But that's the thing...you can't really do this. The updraft associated with a supercell does not scale with the magnitude of the synoptic scale vertical velocity (at any vertical level) in the real world. You can't even do this in the global model world because the model resolution is too coarse to resolve convection, so the model's vv may not necessarily correspond with it trying to show convective vv.

This is not to say that the model's vertical velocity output is completely useless in convective forecasting, as there are things you can infer from it. But one has to be very cautious and keep the above points in mind.

For what it's worth, I don't think this will be a high risk type of tornado outbreak either, but my skepticism has very little to do with the synoptic scale or model output vertical velocities.

At this point as I said, you're not arguing with some hair brain idea I came up with myself. 2 PhD's of meteorology taught this process to me (using the same map/model/website) who are well respected in the academic community for their contribution to modeling of convective processes. I am done defending your guys nit picking of it. Take it up with Markowski and Fritsch if you don't like it.

We are talking about east of the Mississippi too. Supercells are hard to produce, most convection quickly turns into squall lines. I am not taking the model's output of vv's as bible. You use it as a GUIDANCE to get a ROUGH idea/ESTIMATE of the potential strength of the updrafts that will form. Categorically...weak or strong. A supercell or any convective storm's updraft can not compete with synoptic scale forces working against it. It will ultimately lose. You factor the information of potential for strong/weak updrafts in with everything else you look at. It's just another piece of the puzzle.

[QVectorman]

http://www.theweathe...n.com/precipfx/

You can obviously use this and insert -vv's for his comments and figure out the opposite.

METEOROLOGIST JEFF HABY

(1) Study the 700mb vertical velocity progs on the NAM, and GFS, paying close attention to your forecast area. Take note whether the vertical velocity is upwards or downwards. Upward motion (+UVV's) are caused by low level convergence and/or upper level divergence. A UVV of 6 to 9 is moderate, 10+ is large.

(2) Study the 850mb progs and see if your forecast area will be experiencing warm air advection, cold air advection or neutral advection. Low level warm air advection leads to upward vertical velocity while low level cold air advection leads to downward vertical velocity. Neutral thermal advection will neither inhibit nor enhance upward vertical velocity. Examine 1000-mb prog for low level convergence resulting from fronts, topography, low pressure, WAA and moisture advection.

(3) Study the 500mb vorticity panels and see if your forecast area will be experiencing positivevorticity advection or negative vorticity advection. PVA will lead to upward vertical velocity while NVA will lead to downward vertical velocity. Small values of vorticity will neither inhibit nor enhance upward vertical velocity.

(4) Study 300mb panels. See if any jet streaks will influence your forecast region. The divergence sector of a jet streak will lead to upward vertical velocities. These sectors are the right rear and left front quadrants. If the jet is in a highly curved flow, then the divergence occurs anywhere just north of the jet axis in the Northern Hemisphere. If the upper level winds are weak, this will neither inhibit nor enhance upward vertical velocity.

(5) Study thermodynamic diagrams to assess the potential for convective precipitation and precipitation type. Pay attention to moist/dry layers, wind profile, and indices.

(6) Ask yourself which phenomena (WAA, PVA, Streaks) are leading to upward vertical velocity and which phenomena (CAA, NVA, Streaks) are leading to downward vertical velocity.

(7) Take note of the variation between the graphical forecast models on the forecasting of

synoptic scale precipitation.

If vertical velocities are positive, and no precipitation is progged, then there is likely not enough available moisture. Check RH panels to see if uplift is enough to saturate atmosphere. PBLdewpoints can be used to assess how much moisture can be lifted.

(8) Decide whether precipitation is likely or unlikely and decide if severe weather is likely or unlikely. Decide on the following characteristics of the precipitation:

*Convective or stratiform

*Heavy or light

*Widespread or numerous

*Severe or non-severe

*Long lasting or brief

*Wintry or non-wintry

(9) Read NWS convective discussion, zones forecast, state forecast discussion and state forecast.

(10) Examine MOS precipitation data from several synoptic scale forecast models

(11) Look at national and local satellite and radar data as well as a current surface map. Note the features on each of these three sources and ask yourself how they will move through time.

(12) Write out your precipitation forecast, and the expected character of the precipitation if you expect precipitation to occur. Forecast should include amount, duration, type, intensity and other unique characteristics of the precipitation given in (8).

NOTES:

*If vertical velocity is significantly upwards and PVA and jet streaks are not present, then precipitation development is expected to be thermodynamic in origin (low level buoyancy, low level forcing) or the result of low level convergence.

*If vertical velocity is significantly upwards and little WAA or low level convergence is present, then precipitation development is expected to be dynamic in origin (upper level forcing by PVA and / or jet streak).

*If all three +UVV mechanisms are significantly present in the same vacinity (WAA, PVA, Streak), then expect severe storms or heavy precipitation. (must also have low level moisture, deep instability)

*If none of these UVV mechanisms are present, then precipitation can only occur by a mesoscale process (outflow boundaries, sea breeze, orographic lifting, shallow fronts, air mass thermodynamic thunderstorms).

*All forecasting rules of thumbs have exceptions. Add your own intuition to determine precipitation potential.

[audioguy3107]

I know this probably belongs in some type of banter thread, but I personally cannot wait to see what happens tomorrow, not only from the severe aspect, but to see who comes out of this debate with the stronger arguments. This is almost as entertaining as armchair chasing.

[Hoosier]

One of the keys to the magnitude of this event might be how much instability develops farther north in areas closer to the surface low. Looking at the SREF sig tor ingredients, I think that is the main thing holding it back from going bonkers because every other parameter on there is favorable.

Will be curious to see the trends on the 00z runs, particularly if the extreme rapid/quicker deepening trend continues.

[dtk]

You are the data assimilation man, so I am not going to disagree with you, but from a user stand point, the off hour guidance seems to be more prone to odd "blips"/weird runs on occasion, more often than the synoptic guidance, even if scores look identical. That is just my standpoint after using this guidance daily as forecasting tools, and I try my best to remain objective when making criticisms/comments on the guidance. I should note these seem to relatively uncommon as a whole, and I do find off-hour guidance quite useful, especially with intense systems in the short range as they can fill a nice "gap" regarding dprog/dt trends in significant features of a storm--especially feedback scenarios.

Fair enough (though even the scores aren't identical). I suspect that regional models that utilize partial cycling are more susceptible to this type of phenomena than the globals (I've seen for myself some funky things in the NAM, for example, for particular cycles).

I trust your judgement and you may very well be right (particularly for certain types of events). I'm actually glad to hear you say that it is at least relatively uncommon, and I think we definitely agree there.

I just think that perpetuating the notion (regarding the off-hour runs being poor) gives ammunition to folks that want to conveniently disregard solutions that don't agree with their (wishing or) thinking.