Apr. 2-4 Severe Threat

[tornadohunter]

The HRW WRF-ARW likes a long track supercell starting in indiana, crossing into kentucky and then ohio. Interesting...

[IWXwx]

41 minutes ago, andyhb said:

Probabilities seem fine, although I think I'd shift them a bit north too (closer to the track of the surface low).

In my wx briefing to local public safety officials this afternoon, I highlighted my concerns of the warm front stalling in our area, the surface low passing very near us, and the possible implications. I'm on a little higher alert then I normally would be under a slight risk.

[tornado_junkies]

5 minutes ago, tornadohunter said:

The HRW WRF-ARW likes a long track supercell starting in indiana, crossing into kentucky and then ohio. Interesting...

Only problem with that is it looks to be some kind of MCS feature, not necessarily a discrete storm.

[Hoosier]

9 minutes ago, IWXwx said:

In my wx briefing to local public safety officials this afternoon, I highlighted my concerns of the warm front stalling in our area, the surface low passing very near us, and the possible implications. I'm on a little higher alert then I normally would be under a slight risk.

Good approach.  Your area could be a little too far north for the better stuff but it's a close call.  The progged CAPE/shear parameters are sufficient for significant tornado(es), especially the case with any prefrontal development.

[Stebo]

I am also in agreement with respect to warm air aloft adverting in, I don't see it at all.

[tornado_junkies]

7 minutes ago, Hoosier said:

Good approach.  Your area could be a little too far north for the better stuff but it's a close call.  The progged CAPE/shear parameters are sufficient for significant tornado(es), especially the case with any prefrontal development.

I wouldn't be shocked at all to see a significant tornado or two tomorrow in the IN/OH/KY region with any discrete to semi-discrete storm that's able to establish itself in the warm sector or along the WF. 

[Hoosier]

[tornadohunter]

Simulated reflectivity at 12z. Have to imagine that would lay down a boundary or two...

[tornadohunter]

18z 3km NAM is interesting. Tried to fire pre frontal cells by 20z but subsequently kills them by 22z. 

[Tim from Springfield (IL)]

This has been discussed some in the short-term thread, but there is already an Enhanced Risk for tomorrow (Tuesday) from SW OH to NW MS.  Including Cincy, Indy, Louisville, Evansville, Paducah, and Memphis.  Plus Slight up to Toledo and knocking on the doors of CLE and STL:

http://www.spc.noaa.gov/products/outlook/day2otlk.html

 ...Synopsis...
   A compact shortwave trough, accompanied by a strong mid-level jet
   streak, is expected to move through the middle MO Valley and upper
   Midwest/lower OH Valley during the period. An attendant surface low
   will move just ahead of the upper system, moving from its initial
   position near the eastern KS/OK border quickly northeastward through
   the middle MS Valley and into southwestern Ontario. As this occurs,
   a strong cold front will sweep southward/southeastward through much
   of the southern Plains, lower/middle MS Valley, TN Valley, and OH
   Valley. Moisture return ahead of this cold front will result in at
   least modest instability from the southern Plains into the upper OH
   Valley and the expectation is for numerous thunderstorms, some
   severe, to develop along and ahead of this frontal zone at is pushes
   southward/southeastward. 

   ...OH Valley/Mid MS Valley/Southern Great Lakes...
   Showers and thunderstorms will likely be ongoing along and north of
   the warm front (i.e. over mid MS and lower OH Valleys) at the
   beginning of the period. A gradual destabilization of the warm
   sector is anticipated throughout the day as surface temperatures
   warm amidst daytime heating and modest moisture return. Broadly
   confluent southwesterly winds ahead of the front will likely result
   in sporadic warm sector development once convective inhibition is
   eroded. Warm temperatures aloft could mitigate the updraft strength
   of this open warm sector development but strong vertical shear is
   supportive of rotating updrafts with any more persistent
   development. All severe hazards are expected with a tornado or two
   possible, particularly near the warm front. Given uncertainty
   regarding the extent and intensity of the early period
   precipitation, there is some uncertainty to how far north the warm
   front progresses throughout the day. Current expectation is for the
   warm front to lie from central IL eastward into central OH during
   the early afternoon. 

   Greater thunderstorm coverage is then anticipated during the late
   afternoon along, or perhaps just ahead of, the cold front sweeping
   across the region. Strengthening mid-level flow will contribute to
   increasing vertical shear, particularly across the lower OH Valley.
   The best co-location of instability and vertical shear is
   anticipated across the mid MS Valley. In both of these areas, line
   segments capable of damaging wind gusts appear to be the primary
   severe threat. Given the steep mid-level lapse rates noted in
   forecast soundings, some hail is also possible but the linear nature
   of the forcing for ascent suggests a quick transition to a
   predominately linear mode. A tornado or two is also possible,
   particularly across portions of the lower/middle OH Valley, where
   the proximity to the surface low and strong low to mid level winds
   result in more favorable low-level vertical shear.

[Tim from Springfield (IL)]

And I'd be shocked if anything came out of this, but a possible appetizer tonight--a Marginal for S MO/S IL/S IN/SW OH/far N KY:

http://www.spc.noaa.gov/products/outlook/day1otlk.html

...SUMMARY...
   Thunderstorms will occur over parts of the Mid Mississippi and lower
   Ohio Valleys tonight. The strongest cells may produce isolated hail.

   ...20Z Update...
   Thunderstorms are still expected tonight across portions of the
   middle MS and lower OH Valleys as the warm-air advection across the
   frontal zone increases. Guidance still suggests enough instability
   and vertical shear will exist to support updrafts capable of hail
   and no changes are needed to the previous outlook. Additional
   forecast details are available in the discussion appended below.

   ..Mosier.. 04/02/2018

   .PREV DISCUSSION... /ISSUED 1112 AM CDT Mon Apr 02 2018/

   ...Mid MS and Lower OH Valleys...
   Morning water vapor loop shows a strong upper trough moving across
   the northern Great Basin, while a smaller shortwave trough traverses
   NM.  These two features will result in mid-level height falls, lift,
   and increasing coverage of precipitation over the central United
   States this afternoon through tonight.

   Have made several adjustments to the previous outlook based on 12z
   CAM and operational model guidance.  The corridor of highest
   confidence in thunderstorm activity (along with isolated hail
   occurrences) will be from south-central MO late this afternoon into
   parts of southern IL/IN and northern KY tonight.  Forecast soundings
   along this axis show ample elevated CAPE, steep lapse rates, and
   deep-layer shear for at least small hail production, and the
   potential for isolated severe hail in the strongest cells.

   Trends in guidance suggest that the potential for late-night
   development of strong thunderstorms over northwest MO has decreased.
   Also, scattered thunderstorm potential has been added for this
   outlook to parts of the northern Plains and into western VA.

[andyhb]

3 hours ago, tornado_junkies said:

Only problem with that is it looks to be some kind of MCS feature, not necessarily a discrete storm.

Look at the reflectivity, that is definitely not an MCS.

[Stebo]

75 popping on latest SREF tomorrow afternoon

[Hoosier]

Eastern IN at 21z

 

Don't want to overlook closer to the cold front as well for at least some embedded tornado threat.  IND at 00z:

[tornadohunter]

14 minutes ago, Hoosier said:

Eastern IN at 21z

 

Don't want to overlook closer to the cold front as well for at least some embedded tornado threat.  IND at 00z:

Parameters are definitely there. Greensburg, In would be my chase target. Veering winds significantly limit tor threat though. I’d say 5-10 QLCS tors and 2-5 tornadoes along the warm front and/or the warm sector. Maybe 1 significant

[Benadrill]

Hoping I can get a good light show tomorrow night 

[hlcater]

This event has trended somewhat better over the past few days, but directional shear is still lacking due to veered surface winds. I'm not 100% sold on any organized prefrontal storms, but several CAMs have what resembles some sort of prefrontal axis that storms could perhaps organize off of. However, given the 0-1km helicity values well in excess of 300m2s2, I think there is quite the possibility of embedded circulations in the line of storms that looks almost certain to develop along the cold front. What I see with this event is a strongly forced QLCS capable of damaging wind and perhaps some tornadoes. The chance for a significant tornado hinges on whether we can score an organized prefrontal updraft.

[Quincy]

Three regimes for potentially severe convection can be identified from the short-term high resolution models:

1. Warm front from central Indiana to central Ohio.
2. Pre-frontal trough from southern Indiana into western/central Kentucky.
3. Cold front from west to east across the Ohio/Tennessee valleys.

As discussed, positioning of the warm front is a bit of a question mark, although models seem to be converging on a solution. It does look like storm modes may be mixed/messy in this area, but given the degree of wind shear, it won't take much instability for storms to rotate. We're talking about 0-1km shear in excess of 40 knots near the warm front... The question marks will probably boil down to how discrete storms can stay and if any updrafts are able to remain sustained. Given the lack of low level instability, these storms may produce more sporadic severe than anything else, although all severe hazards (hail, wind, tornado) will be possible.

A pre-frontal trough type feature extending south from the warm front and well ahead of the cold front may be the most intriguing aspect of this event. By early and especially mid-afternoon, the parameter space in vicinity of the trough will become increasing supportive of severe thunderstorms. Mid-level warmth is not as big of an issue as it may be farther west, but the biggest question here is how long of a window do updrafts have to be maintained. With eastward extent, the area becomes more and more displaced from stronger large scale forcing, as models suggest that convection may struggle to remain sustained, if develop much at all, south of the OH/KY border. Simulated radar data seems to suggest that although discrete/semi-discrete storm modes will be favored, storms may only have a 2-4 hour window for severe. Even if the window may be somewhat limited, the wind fields could support a relatively long-lived supercell or two (in excess of an hour) with an isolated strong tornado threat. If the warm sector up in southeastern Indiana to southern Ohio remains relatively debris-less through the morning, there may be a narrow area to support a longer-lived severe threat, but mesoscale details will need to be assessed before having any sort of high confidence in such a scenario. Either way, mid-level lapse rates would also support large to possibly very large hail with any robust convection in this vicinity, but such lapse rates do drop off with eastward extent as well, narrowing the threat zone a bit, to if this were later in the season.

The cold front is another interesting case. Wind fields aren't totally unidirectional and there is enough low to mid-level curvature in the hodographs to support embedded supercell structures, if not just a broken line of semi-discrete supercells. This is where mid-level warmth actually becomes a net positive, in terms of severe. In the wake of the pre-frontal trough, some warming in the mid-levels will cap the atmosphere (for the most part) until stronger forcing arrives with the cold front. This means that areas such as southern Indiana and north-western/north-central Kentucky may see some convection around midday or early afternoon, but the area is able to support yet another round of potentially intense convection by late afternoon. Immediately ahead of the cold front, we'll have a scenario where 700-500mb lapse rates should easily be 8 C/km, if not 8.5 C/km or steeper, which is moving into uncharted territory, given climatology. There is actually consensus with the HRRR/HRRRX/3km NAM that at least some area should see these lapse rates reach 9 C/km for a time. That's remarkable. If any supercells near the cold front do remain isolated, very large hail would be possible, as well as a few tornadoes.

Overall, it's a complex setup that holds a lot of potential given the parameter space. Looking at the details, there are multiple areas to watch and it's conceivable that some places could see two rounds of severe convection. Considering parts of the area just had snow yesterday and it's only early April, that would be pretty impressive. There is a fair amount of conditionality involved as well, so I don't think we're going to see a widespread outbreak. With that said, I think there's reason to believe there will be at least a few significant severe storms.

[tornadohunter]

4 minutes ago, Quincy said:

Three regimes for potentially severe convection can be identified from the short-term high resolution models:

1. Warm front from central Indiana to central Ohio.
2. Pre-frontal trough from southern Indiana into western/central Kentucky.
3. Cold front from west to east across the Ohio/Tennessee valleys.

As discussed, positioning of the warm front is a bit of a question mark, although models seem to be converging on a solution. It does look like storm modes may be mixed/messy in this area, but given the degree of wind shear, it won't take much instability for storms to rotate. We're talking about 0-1km shear in excess of 40 knots near the warm front... The question marks will probably boil down to how discrete storms can stay and if any updrafts are able to remain sustained. Given the lack of low level instability, these storms may produce more sporadic severe than anything else, although all severe hazards (hail, wind, tornado) will be possible.

A pre-frontal trough type feature extending south from the warm front and well ahead of the cold front may be the most intriguing aspect of this event. By early and especially mid-afternoon, the parameter space in vicinity of the trough will become increasing supportive of severe thunderstorms. Mid-level warmth is not as big of an issue as it may be farther west, but the biggest question here is how long of a window do updrafts have to be maintained. With eastward extent, the area becomes more and more displaced from stronger large scale forcing, as models suggest that convection may struggle to remain sustained, if develop much at all, south of the OH/KY border. Simulated radar data seems to suggest that although discrete/semi-discrete storm modes will be favored, storms may only have a 2-4 hour window for severe. Even if the window may be somewhat limited, the wind fields could support a relatively long-lived supercell or two (in excess of an hour) with an isolated strong tornado threat. If the warm sector up in southeastern Indiana to southern Ohio remains relatively debris-less through the morning, there may be a narrow area to support a longer-lived severe threat, but mesoscale details will need to be assessed before having any sort of high confidence in such a scenario. Either way, mid-level lapse rates would also support large to possibly very large hail with any robust convection in this vicinity, but such lapse rates do drop off with eastward extent as well, narrowing the threat zone a bit, to if this were later in the season.

The cold front is another interesting case. Wind fields aren't totally unidirectional and there is enough low to mid-level curvature in the hodographs to support embedded supercell structures, if not just a broken line of semi-discrete supercells. This is where mid-level warmth actually becomes a net positive, in terms of severe. In the wake of the pre-frontal trough, some warming in the mid-levels will cap the atmosphere (for the most part) until stronger forcing arrives with the cold front. This means that areas such as southern Indiana and north-western/north-central Kentucky may see some convection around midday or early afternoon, but the area is able to support yet another round of potentially intense convection by late afternoon. Immediately ahead of the cold front, we'll have a scenario where 700-500mb lapse rates should easily be 8 C/km, if not 8.5 C/km or steeper, which is moving into uncharted territory, given climatology. There is actually consensus with the HRRR/HRRRX/3km NAM that at least some area should see these lapse rates reach 9 C/km for a time. That's remarkable. If any supercells near the cold front do remain isolated, very large hail would be possible, as well as a few tornadoes.

Overall, it's a complex setup that holds a lot of potential given the parameter space. Looking at the details, there are multiple areas to watch and it's conceivable that some places could see two rounds of severe convection. Considering parts of the area just had snow yesterday and it's only early April, that would be pretty impressive. There is a fair amount of conditionality involved as well, so I don't think we're going to see a widespread outbreak. With that said, I think there's reason to believe there will be at least a few significant severe storms.

So the SPC in Norman should hire Q. Nice write up Q. 

Is the lack of forcing why the 3k nam kicks off some pre frontal activity but diminishes rapidly? Latest HRRR tries to get a few pre frontal cells as well...

[Hoosier]

First warning for quarter size hail just south of St. Louis.

[tornado_junkies]

Well, HRRRX certainly looks interesting.

[RCNYILWX]

Some interesting top CIPS analogs based off 00z NAM, #1 is 4/19/11, #2 was an active day on 4/4/03 and #6 is 3/2/12. A few other pretty big days mixed in among the top 15 as well.

Sent from my SM-G935V using Tapatalk

[Quincy]

10 minutes ago, RCNYILWX said:

Some interesting top CIPS analogs based off 00z NAM, #1 is 4/19/11, #2 was an active day on 4/4/03 and #6 is 3/2/12. A few other pretty big days mixed in among the top 15 as well.

Sent from my SM-G935V using Tapatalk
 

4/19/11 is an example of what this event would look like if it were later in the season and the downstream pattern was more favorable (larger, much more unstable warm sector), and near-surface winds were more backed. Nearly everything was going for that event. It is interesting to note that deep layer shear orientation to the cold front is very similar to what's expected tomorrow. Some of the bigger differences come in the warm sector.

[andyhb]

1 hour ago, Quincy said:

4/19/11 is an example of what this event would look like if it were later in the season and the downstream pattern was more favorable (larger, much more unstable warm sector), and near-surface winds were more backed. Nearly everything was going for that event. It is interesting to note that deep layer shear orientation to the cold front is very similar to what's expected tomorrow. Some of the bigger differences come in the warm sector.

I'd tend to think the shear magnitude here is on an order above that one, despite CAPE being substantially less. 4/2011 was a truly incredible month thermodynamically.

[Chicago Storm]

This is not a 10% hatched kind of day.

Broyles’d again.


.

[OHweather]

27 minutes ago, Chicago Storm said:

This is not a 10% hatched kind of day.

Broyles’d again.


.

I'm on the fence.  I think the parameter space is there for a significant tornado, but questions over whether or not the storm mode remains too messy are still there and are what give me some doubt.  Edwards definitely wrote the body of that outlook text.  The HRRR does have perhaps enough semi-discrete cells that it'd be an issue...could be a situation where one or two cells can take full advantage of the environment for a time and produce while everything else remains messy. 

Congrats on the new tag btw. 

[buckeye]

If this warm front doesn't start moving it's butt a little quicker,  radar indicates there's going to be some pretty impressive rainfall totals along i-70 between Indy and CMH.

[tornadohunter]

Sat shows a nice clearing over sw Indiana and temps are soaring...

Dews already in the high 50s...

[andyhb]

1 hour ago, Chicago Storm said:

This is not a 10% hatched kind of day.

Broyles’d again.


.

Care to offer a reason why? Broyles was not the only one on that forecast.

Usually when you see the SREF tornado ingredients popping a 90...there's some credence to a significant tornado threat.

[tornadohunter]

Sounding off latest HRRR for NE of Connorsville, In at 22z