April 14-17th Severe Weather (Day 3 Mod)

[patrick7032]

I didn't see this posted...so if I missed it bare with me...but one of our forecasters at the office came across this link which I found interesting. It deals with past day 3 MODS issued since 2000.

 

http://www.pmarshwx.com/2012/04/spc-day-3-moderates-in-context-what-do-they-become/

[yoda]

I think that was his way of saying, "we think the warm front may surge northward, but we aren't sure, so we will make it sound colder than it is to add emphasis". 

 

Thats what i figured as well... just seemed like an odd way to word how cold it was

[baroclinic_instability]

00z ECMWF is clear to the N OK/S KS border with the warm front, absolutely lights up the dryline (albeit a bit early).

[andyhb]

00z ECMWF is clear to the N OK/S KS border with the warm front, absolutely lights up the dryline (albeit a bit early).

 

Yeah I thought it might with that setup at the sfc and aloft.

 

Man, there is multiple rounds of that stuff as well from the looks of it...

[chase_stormz]

00z ECMWF is clear to the N OK/S KS border with the warm front, absolutely lights up the dryline (albeit a bit early).

 

how early? like early afternoon? 

[JoMo]

By 15z Wed, the Euro has the warm front along the KS/OK border. This is farther NW than it's 12z run. Precip breaking out in E OK and along the dryline but there's enough CAPE around for those to be severe....... Looks like a long day severe weather wise with multiple rounds possible. 

[baroclinic_instability]

how early? like early afternoon? 

Verbatim ECMWF, it is developing convection in the vicinity of the dryline as early as noon.

[chase_stormz]

Verbatim ECMWF, it is developing convection in the vicinity of the dryline as early as noon.

where is the dryline location at that time?

[baroclinic_instability]

where is the dryline location at that time?

Across the eastern TX Panhandle. It is all free here: http://www.wunderground.com/wundermap

 

 Just choose model data on right hand side, then ECMWF. 

[patrick7032]

Since SPC changed the SREF model...how good is a 60 value based on what everyone has seen? Even see a "hint" of 80 in southern Oklahoma.

[JoMo]

You guys in Norman feel the Earthquake?

[thewxmann]

Last three Euro runs...

 

 

 

[chase_stormz]

Last three Euro runs...

 

trending north i see..

[baroclinic_instability]

One major caveat that others have hinted at, and that one could expect with deep layer SW flow with a very well defined sloping warm front, is the potential for large areas of elevated convection across the ascending branch of the WCB. As one can expect with a broad zone of SW flow...lapse rates as indicated by all models will be approaching dry adiabatic through the midlevels with ample WAA ascent and moisture advection...especially Wed morning as the central/southern plains comes under the influence of an increasingly favorable region of the anticyclonic jet max to the N. All these combined would yield an environment favorable for potentially extensive elevated morning/early afternoon convection, with some of the models going as far to (i.e., the high res NAM) to suggest the potential formation of an early mesoscale convective system that slides east across OK through the day. I do believe there is a legitimate possibility for large amounts of crapvection to play a negative role in the overall setup...and will likely come down to last minute short term forecasting to determine how quickly and when the elevated convection clears east...and how it affects the thermodynamics and possibly local scale circulations. I do believe some of the activity the ECMWF is initiating is not legitimate dryline convection but early morning elevated, and it hints at the possibility that some of that activity congeals into larger clusters with time. Some potential caveats to consider.

 

 

SREF lapse rates Wed morning:

 

06z NAM jet:

 

00z GFS 309 K Isentropic/mixing ratio Wed morning:

 

06z NAM 850 hpa theta-e axis Wed morning:

[baroclinic_instability]

Animation of 06z NAM 250 hpa jet Wed morning into the afternoon. Note both the STJ nosing in late...and the increasingly favorable right entrance to the northern stream through mid morning. If elevated convection does not ruin the warm sector...it is pretty easy to see the incredible area of vertical forcing much of the mod risk area will be under...with a very impressive dual jet (especially the left exit of that 140 kt STJ).

 

[Buckeye05]

Didn't April 14, 2012 start off with a lot of morning convection, including a bunch of messy junk? I was umm..skeptical to say the least after seeing that. Despite that, I remember we ended up seeing multiple rounds with that one, each stronger than the last. Not directly comparing the two, just food for thought.

[baroclinic_instability]

06z GFS remains north of everything, and it even managed to lift the front farther N into Kansas late Wed with a sub 994 hpa low across the western OK Panhandle. Most notably, the GFS clears out potential elevated convection early, and erodes capping near the dryline by late afternoon. Long, clockwise hodographs, low MLLCLs, very steep low level lapse rates, stronger upper level flow nosing in as the STJ advances east. I don't have EHI's available, but my guess is they are off the charts. Straight 06z GFS would be a potential tornado outbreak east of the dryline.

[brettjrob]

Didn't April 14, 2012 start off with a lot of morning convection, including a bunch of messy junk? I was umm..skeptical to say the least after seeing that. Despite that, I remember we ended up seeing multiple rounds with that one, each stronger than the last. Not directly comparing the two, just food for thought.

 

Yes. I've been adamant the last couple days that early warm sector convection won't be the end of the story for this threat. There are plenty of examples (4/14/12 and 5/5/07 immediately come to mind) in which, due to rich low-level moisture and very strong advection, an outbreak has still followed widespread morning dryline storms.

 

The difference when compared against 4/14/12 is the cold air lingering close by. Widespread elevated convection could have the effect of holding the boundary farther S than would otherwise be the case. Last year, the warm front was already clear into NE/IA the morning of the outbreak, hundreds of miles N of the main dryline action.

 

Glancing at current sfc obs, I must reluctantly admit I'm starting to share Tony's and Jim's concerns more seriously. This is such a typical mode of failure for events outside of the main Plains season (late April-June), and one that has absolutely trashed otherwise-tantalizing setups many times historically. We currently have 35/23 with a NE wind at 16 mph in the OK Panhandle. I don't see the front retreating into KS (at least W of US-81), so the question for me is whether it can at least make it significantly NW of I-44. Taking convection-resolving models like the 4 km WRF variants into account, that becomes a legitimate question.

 

[baroclinic_instability]

Yes. I've been adamant the last couple days that early warm sector convection won't be the end of the story for this threat. There are plenty of examples (4/14/12 and 5/5/07 immediately come to mind) in which, due to rich low-level moisture and very strong advection, an outbreak has still followed widespread morning dryline storms.

 

The difference when compared against 4/14/12 is the cold air lingering close by. Widespread elevated convection could have the effect of holding the boundary farther S than would otherwise be the case. Last year, the warm front was already clear into NE/IA the morning of the outbreak, hundreds of miles N of the main dryline action.

 

Glancing at current sfc obs, I must reluctantly admit I'm starting to share Tony's and Jim's concerns more seriously. This is such a typical mode of failure for events outside of the main Plains season (late April-June), and one that has absolutely trashed otherwise-tantalizing setups many times historically. We currently have 35/23 with a NE wind at 16 mph in the OK Panhandle. I don't see the front retreating into KS (at least W of US-81), so the question for me is whether it can at least make it significantly NW of I-44. Taking convection-resolving models like the 4 km WRF variants into account, that becomes a legitimate question.

 

tmfwnd36.png

I do share, to some degree, those concerns. We would be bad mets if we simply ignored potential failure modes. I will say synoptically this is a favorable setup for a rapid return, however, as the relatively low amplitude northern stream wave rapidly translates eastward and we almost immediately begin to build upper height rises as mid level warm air advection commences.  That surface ridge axis should rapidly weaken, and upstream soundings in the cold air do not exhibit classic arctic air mass characteristics. This is not the classic high pressure arctic ridge with a strong upper level trof across the east coast and cold, dense air plunging through the plains. Diurnal insolation alone will do a number on that airmass/ridge pretty quickly. The big caveat/question will indeed be the effect of late evening/overnight convection. It should be noted the very long sloping warm front the models are progging...there is the possibility elevated DMC along the nose of the LLJ remains well N of the low level boundary. I don't share your extensive experience in the S Plains, but I feel the larger caveat may be potential mid morning convection clustering into larger segments...wiping out the warm sector and creating unfavorable vertical circulations. I don't see this front getting shunted like the NAM suggests.

 

Edit: That low stratus deck under the inversion may be more of a problem, however. There is a legit chance that hangs around until Wed. They have a tendency to be tough to erode. My guess is we will be evaluating how quickly that erodes during the day Wed.

[baroclinic_instability]

That stratus deck is deep, very deep. 

[brettjrob]

12z NAM has the cold wedge about 60-70 mi. S of last night's run in the Panhandle and SW OK. Thinking Wed. might be starting to come off the rails.

[tornadotony]

If the moderate risk area verifies anything more than a low-end to maybe middle-of-the-road slight risk tomorrow, I'll eat a shoe.  Given the orientation of that warm front, even if there are good parameters in the warm sector, I don't expect they'd be fully tapped, given either a 2/10/09 scenario I discussed yesterday or upscale growth into a convective mess.

[baroclinic_instability]

12z NAM has the cold wedge about 60-70 mi. S of last night's run in the Panhandle and SW OK. Thinking Wed. might be starting to come off the rails.

The 12z NAM still eventually ends up farther N than both the 00/06z runs, but yeah, low stratus is going to be challenging to forecast how far it eventually erodes. 

[Buckeye05]

Well it seems that confidence is dropping here, with all these potential caveats stacking up. Think we could see the MOD dropped tomorrow morning?

[OSUmetstud]

I think the set up favors multiple rounds of severe convection along with lewps and hp supercells.  Might be a tough chase day as tornadoes could be embedded within the hp supercells and lewps.  Coverage of severe weather should be very good but the highest end potential of strong tornadoes could be squandered.

[OSUmetstud]

I'd think that SW OK and far northern TX has the best potential of strong tornadoes.  That area would be further removed from the isentropic lift and have more potential for decent heating in the mid/late afternoon.  

[baroclinic_instability]

Well it seems that confidence is dropping here, with all these potential caveats stacking up. Think we could see the MOD dropped tomorrow morning?

Doubt it...unless the front is clearly not going to make northward progression. The low stratus deck is a worry, but there remains continued northward trend in every piece of numerical guidance. The high will be rapidly weakening, and broad scale mass ascent will aid in weakening the inversion. That said, there are no guarantees to how far it erodes. I would surprised if SPC dropped the mod given the potential. Going day 3 mod, in some ways, put them into this bind. 

[OUGrad05]

Well it seems that confidence is dropping here, with all these potential caveats stacking up. Think we could see the MOD dropped tomorrow morning?

I think it's far too early to call that.  There's a wide discrepancy betweent he models at this point but even the NAM is bringing the front back to just north and west of I44 in SW OK and just west of I35 by 6pm tomorrow.  Upper end severe probabilities may prove to be limited with ongoing convection and/or cloud deck tomorrow morning.  But it seems likely that there will be severe weather tomorrow even if the front only makes it back to the NAM solution.  If it's much farther south that woudl be problematic but I'm not willing to throw in the towel on this just yet.

[OSUmetstud]

I'd go with the euro frontal position any day of the week over the NAM at 36 hours...but that's just me

[baroclinic_instability]

I'd go with the euro frontal position any day of the week over the NAM at 36 hours...but that's just me

The ECMWF is having as much difficulty with this setup as all the other models. Sensitivity to latitude of the wave ejection, boundary layer params, vertical levels and subsequent depiction of the lee low, elevated convection (and the various params) mean it is not a good idea to ride any one model. The NAM and ECMWF are the two most similar operational models with respect to the southern WF placement here.