May 7th-10th Severe Outbreaks

[andyhb]

Time to get this thread off the ground with what seems to be shaping up as a multi-day threat for the Southern Plains starting on Thursday/Friday as multiple lead impulses eject out ahead of the southwestern upper low, leading to periodic cyclogenesis and associated LLJ intensification with adequate instability/moisture/deep layer shear in place. I like both days for some good chaser events, perhaps with handfuls of tornadoes each thanks to favorably low LCL heights and backing low level flow, particularly in Texas (perhaps into OK on Friday as well).

 

The focus then turns to Saturday and Sunday as the primary system ejects towards the Plains. Models continue to waffle in timing and track of the system especially by Sunday, but the overall synoptic pattern would suggest potential for a bigger event, although there are a number of things that need to be worked out, as always, for that (antecedent convection, details of the wind fields, etc). This week does look to be the best so far we've seen for a sustained favorable period for chasers and it may continue beyond that based on ensemble guidance. May is arriving...

[Quincy]

No real surprise, but 30% severe probabilities up from SPC now from north Texas up into northern Kansas for Saturday, day 4. Day 5 has a 15% risk from northeast Texas to central Iowa.

[Ground Scouring]

For Saturday (9 May), I see a lot of problems with this set-up, +PDO/drought climatology and past performance not least, but also including the potential for back-veer-back at 850-500 mb, the relatively weak wind fields (making mesoscale factors like moisture return all the more critical), and the likelihood for drier low-level air to scour out low-level moisture in the eastern Gulf (thanks to our developing subtropical sloppy off the SE coast). The high model variability in the short term would favor the ECMWF solution, which is slower and delays the arrival of more significant large-scale forcing until early evening. If other factors conspire against this set-up, then the slower arrival of forcing would be a deal-killer. While early signs in other respects may appear promising, I would bet on a combination of a few factors limiting the tornado threat to perhaps a few brief touchdowns. I could be wrong, but I would not bet against the seasonal trend.

[andyhb]

For Saturday (9 May), I see a lot of problems with this set-up, +PDO/drought climatology and past performance not least, but also including the potential for back-veer-back at 850-500 mb, the relatively weak wind fields (making mesoscale factors like moisture return all the more critical), and the likelihood for drier low-level air to scour out low-level moisture in the eastern Gulf (thanks to our developing subtropical sloppy off the SE coast). The high model variability in the short term would favor the ECMWF solution, which is slower and delays the arrival of more significant large-scale forcing until early evening. If other factors conspire against this set-up, then the slower arrival of forcing would be a deal-killer. While early signs in other respects may appear promising, I would bet on a combination of a few factors limiting the tornado threat to perhaps a few brief touchdowns. I could be wrong, but I would not bet against the seasonal trend.

 

Except that this system really is too weak/too far east to thoroughly impact the main moisture trajectories for this system. Heck we have upper 60s dewpoints to the Red River already and plenty of deep layer moisture today and this was the day I was most concerned about that system impacting this.

 

The wind profile issue with the veer-back-veer is currently fairly subtle, although obviously this could change (it is almost always a concern so I don't see how this is something new). Wind field strength is something we won't get all the details of until closer in. I get the impression that the slower arrival of forcing might just shift the setup to the west rather than eliminating it (and might make Sunday a bigger deal for that matter).

 

How is the +PDO/drought climatology/seasonal trend going to prevent/hinder a bigger event if the ingredients come together? That makes no sense. You do realize how much rain the Southern Plains have received over the last few months, right?

[brettjrob]

Yeah, I don't think I agree with almost anything in that post. Drought is irrelevant, as the entire southern Plains have been absolutely deluged for the past 2-3 weeks and ET should be as good as you'll see this time of year. I'm just about fully onboard the #hypetrain for Saturday. It currently looks like a synoptically-evident outbreak, especially given the moisture quality and time of year. There are caveats, as always, but I think they'll simply modulate the severity of what's almost certainly a significant event (without major changes in the final 84 h). I'll go out on a limb and say this is "at least" a MDT risk event by D1, unless the absolute worst-case scenario regarding morning convection verifies (e.g., a massive, sweeping MCS moves through starting at sunrise and pinches off the warm sector as much as possible).

[andyhb]

I'm just about fully onboard the #hypetrain for Saturday.

 

I'm liking tomorrow and Friday more and more as well.

[Ian]

Agree with Brett. Mod tor seems a given Sat. High wouldn't be surprising.

[Stebo]

Yeah, I don't think I agree with almost anything in that post. Drought is irrelevant, as the entire southern Plains have been absolutely deluged for the past 2-3 weeks and ET should be as good as you'll see this time of year. I'm just about fully onboard the #hypetrain for Saturday. It currently looks like a synoptically-evident outbreak, especially given the moisture quality and time of year. There are caveats, as always, but I think they'll simply modulate the severity of what's almost certainly a significant event (without major changes in the final 84 h). I'll go out on a limb and say this is "at least" a MDT risk event by D1, unless the absolute worst-case scenario regarding morning convection verifies (e.g., a massive, sweeping MCS moves through starting at sunrise and pinches off the warm sector as much as possible).

Completely agree with this. Moisture definitely will not be a problem at this point for Saturday.

[Ground Scouring]

While I'll concede that the drought has been alleviated somewhat, the long-term conditions (per U.S. Drought Monitor) still indicate a fairly substantial area of ≥D2 conditions over the TX Panhandle/N TX, western OK, and extreme southwestern KS. Although recent trends are in the right direction, we will need to see much more substantial rainfall over a longer period of time--and over a wider section of the worst-impacted areas. Tonight's heaviest rainfall (especially in the OKC metro) is mostly falling outside the worst drought areas mentioned previously. The Red River area of N TX / SW OK needs a lot more rain than it is currently receiving. So I will still stand by my statements, with a modification that the drought conditions, as I mentioned, are but one factor.

 

While Saturday, 9 May, may see a widespread severe event, whether it is chase-worthy will still depend on the other caveats (non-drought-related) that I and others mentioned. As of now, I do not like the relatively weak deep-layer shear on the models, which is not much greater than that which occurred today over the warms sector. Thus, we may well see many HP events with the supercells that go tornadic. We will need to see major changes in both the ECMWF and GFS solutions toward stronger wind profiles to offset this threat. The back-veer-profile will obviously be a concern as well, even though trends indicate that early convection may (and that is a big if) not be a significant impediment to the overall set-up. And overall trends favoring a delay in the arrival of stronger forcing are a third negative factor. So we will need to see changes in both the timing (unlikely as the ECMWF is superior within 84 hr) and the form (also somewhat unlikely) of the trough on 9 May.

[andyhb]

While I'll concede that the drought has been alleviated somewhat, the long-term conditions (per U.S. Drought Monitor) still indicate a fairly substantial area of ≥D2 conditions over the TX Panhandle/N TX, western OK, and extreme southwestern KS. Although recent trends are in the right direction, we will need to see much more substantial rainfall over a longer period of time--and over a wider section of the worst-impacted areas. Tonight's heaviest rainfall (especially in the OKC metro) is mostly falling outside the worst drought areas mentioned previously. The Red River area of N TX / SW OK needs a lot more rain than it is currently receiving. So I will still stand by my statements, with a modification that the drought conditions, as I mentioned, are but one factor.

 

You should really stop with this. I don't have time to pick this apart, but the drought has basically become a moot point at this juncture. Have you not seen the tornadic activity over W TX this year?

 

I don't want to bring up anecdotes, but your material before the 4/27-28 event last year and then the constant downplaying (even clearly making things up at times without looking at the data) during both the Atlantic and E Pacific tropical seasons is making me question your judgment.

 

The 18z GFS is showing 40-50 kts of 0-6 km shear across the dryline at 00z Sunday. Also, your analysis of veer-back-veer/back-veer-back limiting the tornado potential around OKC today didn't make any sense. I went to mesoanalysis and there was no trace of it where you were indicating. I don't know if you're trolling with this "anti-weenie" moniker you've adopted, but stop, seriously.

[Stebo]

While I'll concede that the drought has been alleviated somewhat, the long-term conditions (per U.S. Drought Monitor) still indicate a fairly substantial area of ≥D2 conditions over the TX Panhandle/N TX, western OK, and extreme southwestern KS. Although recent trends are in the right direction, we will need to see much more substantial rainfall over a longer period of time--and over a wider section of the worst-impacted areas. Tonight's heaviest rainfall (especially in the OKC metro) is mostly falling outside the worst drought areas mentioned previously. The Red River area of N TX / SW OK needs a lot more rain than it is currently receiving. So I will still stand by my statements, with a modification that the drought conditions, as I mentioned, are but one factor.

 

While Saturday, 9 May, may see a widespread severe event, whether it is chase-worthy will still depend on the other caveats (non-drought-related) that I and others mentioned. As of now, I do not like the relatively weak deep-layer shear on the models, which is not much greater than that which occurred today over the warms sector. Thus, we may well see many HP events with the supercells that go tornadic. We will need to see major changes in both the ECMWF and GFS solutions toward stronger wind profiles to offset this threat. The back-veer-profile will obviously be a concern as well, even though trends indicate that early convection may (and that is a big if) not be a significant impediment to the overall set-up. And overall trends favoring a delay in the arrival of stronger forcing are a third negative factor. So we will need to see changes in both the timing (unlikely as the ECMWF is superior within 84 hr) and the form (also somewhat unlikely) of the trough on 9 May.

The drought isn't going to be an issue, I am not sure why you are still going down that road. Today proved that moisture isn't an issue, and that is not including all the rain that has fallen. If there are any caveats to Saturday it is early initiation or morning convection, though the latter of the two has been going away on the models except for the Euro. Early Initiation isn't a complete deal breaker though as anything that goes will probably be significant. As for the wind fields, they are forecast to be stronger on Saturday than they were today, and we are around 40 tornado reports for today.

[andyhb]

If there is any indication of the moisture, today is a great one, since we still have 6 tornado warnings well after dark in the Plains. The deep boundary layer moisture/strong low level flow is helping keeping it coupled.

[jojo762]

Not sure how having widespread upper 60's DP's/lower 70's will create a problem at all. (As all models indicate really).. Lmao the shear argument also makes no sense at all, all the models indicate at least moderate shear really.

[andyhb]

00z GFS lights up a string of pearls at 21z in W KS/OK on Saturday along the dryline. CAPE of 2000-3000 J/kg (actually increases at bit by 00z Sunday) and low level wind profiles seem solid without looking at any forecast soundings yet (if you add surface backing into the picture). I am not seeing why it isn't backing the surface winds given the orientation/location/deepening of the lee cyclone through the day Saturday, then again it didn't show this along the warm front on 4/9 in N IL and we know how that worked out. However, veer-back-veer is becoming prominent in the GFS forecast soundings, which could throw a big wrench in things.

 

I'll add that the 00z NAM (72 hrs out so take what you will) would likely be a high end event in this same corridor (lights up the same stretch with supercells and stronger low level shear).

[tornadotony]

Saturday is about as synoptically-evident as it gets for the southern Plains, and we are as distanced as the Cubs are from their last World Series win to having BL moisture being a problem.  Any talk of that is complete hogwash.  Any talk of drought being a factor shows complete ignorance to mesoscale meteorology and to what is currently already occurring.  Upper-level flow appears sufficient, if not better than today (and, hello, we just had an outbreak with multiple large tornadoes).  Low-level flow appears to remain backed given the strengthening low and the and the negative-tilt shortwave trough associated with the upper-level low.  The GFS and NAM both paint pretty significant precip east of I-35, but southerly low-level flow and EML advection aloft should counteract any stabilizing effects of that activity W of I-35.  Simply put, Saturday probably has the potential to be a classic tornado outbreak for Oklahoma between the TX Panhandle border and I-35, maybe the most intense Plains event in several years.

[tornadotony]

00z GFS lights up a string of pearls at 21z in W KS/OK on Saturday along the dryline. CAPE of 2000-3000 J/kg (actually increases at bit by 00z Sunday) and low level wind profiles seem solid without looking at any forecast soundings yet (if you add surface backing into the picture). I am not seeing why it isn't backing the surface winds given the orientation/location/deepening of the lee cyclone through the day Saturday, then again it didn't show this along the warm front on 4/9 in N IL and we know how that worked out. However, veer-back-veer is becoming prominent in the GFS forecast soundings, which could throw a big wrench in things.

 

I'll add that the 00z NAM (72 hrs out so take what you will) would likely be a high end event in this same corridor (lights up the same stretch with supercells and stronger low level shear).

I feel the veer-back-veer on the GFS is likely due to convective feedback.  While there will likely be significant convection to the east of the interest area, and it will have some effect on upper-level flow, I don't know that it will have as significant of an effect on upper-level flow as the GFS suggests.  The NAM also develops significant precip, but it appears to be a little more realistic than the GFS.  The result is no veer-back-veer profiles during the peak time of interest.  It can be a gamble, and it's something to watch, but for right now, I'd trust the NAM more with upper-level flow progs than I would the GFS.

[andyhb]

I feel the veer-back-veer on the GFS is likely due to convective feedback.  While there will likely be significant convection to the east of the interest area, and it will have some effect on upper-level flow, I don't know that it will have as significant of an effect on upper-level flow as the GFS suggests.  The NAM also develops significant precip, but it appears to be a little more realistic than the GFS.  The result is no veer-back-veer profiles during the peak time of interest.  It can be a gamble, and it's something to watch, but for right now, I'd trust the NAM more with upper-level flow progs than I would the GFS.

 

Good stuff. I need to check the Euro to see if this is prominent as well, my guess is that it might be closer to the NAM.

 

Thinking Friday could be a substantial, possibly widespread "lead-up" day too. That lead impulse that ejects is pretty healthy looking. Tomorrow might be a bit more localized particularly WRT tornado potential, but chasers should be licking their chops for this upcoming period (following a tornado outbreak no less).

 

Edit: Appears Carbin agrees with me for Friday, heh. Enhanced risk added and 30% sig hatched. Mention of a possible upgrade once mesoscale details become clearer.

[RCNYILWX]

Southern Plains CIPS analogs off 00z GFS for Saturday are pretty incredible/ominous and certainly indicative of the potential that's been discussed. 84 sig and 122 long track tors amongst top 15. 4/14/12 is currently #3 analog.

[andyhb]

Discussion for tomorrow's threat has been moved here at my request.

[Torchageddon]

Just for the few seconds I was looking at the SPC page, they went MOD for Saturday right before my very eyes  .

[andyhb]

D3 moderate added for Saturday, will post for posterity.

 

DAY 3 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK
0255 AM CDT THU MAY 07 2015

VALID 091200Z - 101200Z

...THERE IS A MDT RISK OF SVR TSTMS ACROSS PORTIONS OF OKLAHOMA AND
KANSAS...

...THERE IS AN ENH RISK OF SVR TSTMS AROUND THE MDT RISK AREA FROM
NORTH TX TO KANSAS...

...THERE IS A SLGT RISK OF SVR TSTMS AROUND THE ENH RISK AREA FROM
TX RIO GRANDE VALLEY TO WRN MO AND WEST TO A SMALL PART OF ERN CO...

...THERE IS A MRGL RISK OF SVR TSTMS FROM TX TO THE MIDWEST...

...SUMMARY...
A SEVERE WEATHER OUTBREAK APPEARS POSSIBLE ACROSS PARTS OF THE GREAT
PLAINS ON SATURDAY. WIDESPREAD INTENSE THUNDERSTORMS SHOULD DEVELOP
OVER PORTIONS OF OKLAHOMA...KANSAS...AND TEXAS DURING THE AFTERNOON.
TORNADOES...VERY LARGE HAIL...AND DAMAGING WINDS ARE LIKELY IN THESE
AREAS.

...SOUTHERN AND CENTRAL PLAINS...
THERE IS INCREASING CONFIDENCE IN THE LARGE SCALE PATTERN EVOLUTION
ACROSS THE SRN AND CENTRAL PLAINS THROUGH SATURDAY AS A POTENT AND
PROGRESSIVE MID/UPPER DISTURBANCE EMERGES FROM THE ROCKIES AND
SPREADS HEIGHT FALLS/ASCENT AND STRONG SHEAR ACROSS A WARM AND
UNSTABLE AIRMASS.

BY LATE SATURDAY AFTERNOON...THE INGREDIENTS SHOULD COME TOGETHER TO
SUPPORT A SEVERE WEATHER OUTBREAK ACROSS THE SRN/CENTRAL PLAINS.
ALTHOUGH THERE REMAIN UNKNOWN DETAILS WITH RESPECT TO MOST
SIGNIFICANT THREAT AND STORM EVOLUTION...GENERAL PATTERN RECOGNITION
AND REMARKABLE AGREEMENT IN LATEST GUIDANCE WITH RESPECT TO LARGE
SCALE FORCING FOR ASCENT ASSOCIATED WITH HEIGHT FALLS/UPPER TROUGH
AND JUXTAPOSITION OF INSTABILITY AXIS...AND CLIMATOLOGY...ALL
SUPPORT A RELATIVELY HIGH CONFIDENCE FORECAST OF NUMEROUS INTENSE
STORMS/SUPERCELLS CAPABLE OF PRODUCING VERY LARGE/DAMAGING HAIL AND
A FEW STRONG/LONGER-LIVED TORNADOES IN THE MODERATE RISK AREA.

THIS SCENARIO WILL UNFOLD AMIDST A VERY MOIST WARM SECTOR WHERE SFC
DEW POINTS AROUND 70F SHOULD RESIDE AHEAD OF A SHARPENING DRYLINE
EXTENDING SOUTH FROM DEEPENING LEE CYCLONE FROM SWRN KS SWD INTO W
TX. 50-60 KTS OF SWLY 500 MB FLOW WILL PIVOT AROUND MID/UPPER LOW
AND ACROSS OK/KS AS A SFC LOW CONTINUES TO STRENGTHEN THROUGH EARLY
EVENING. BACKED LOW LEVEL FLOW BENEATH THE STRONG SWLY 500MB FLOW
WILL RESULT IN HIGH SRH SUPPORTIVE OF POTENTIAL STRONG TORNADOES AS
WELL AS VERY LARGE HAIL. INITIAL DISCRETE CONVECTION SHOULD GROW
UPSCALE INTO CLUSTERS OR LINES THROUGH THE EVENING WITH SEVERE
WIND...HAIL...AND FLOODING THREATS CONTINUING INTO THE NIGHT EAST
ACROSS THE MISSOURI VALLEY AND SOUTH INTO TX.

..CARBIN.. 05/07/2015

[CoastalWx]

That's a classic look for an outbreak. Probably one of those deals where you pick your poison chasing. Western Kansas will probably have a ton of SRH, but stuff may line out quicker due to better forcing. Perhaps faster moving as well. Srn end a bit more capped, but more discrete cells. Pretty awesome.

[Quincy]

For today...winds are fairly backed across most of Texas as of 6 a.m. In the vicinity of a boundary draped from Caprock to near the Red River down to DFW, winds are SE to E. I'll be curious to see some satellite imagery soon, because that might be one of several features to locally enhance the threat today. The HRRR is going bonkers suggest least 4 to 5 corridors of storm initation this afternoon. Will post some 12z soundings as they are released.

[Quincy]

One of the better looking soundings at 12z was AMA. FWD had strong low level directional shear, but was also fairly saturated. OUN was contaminated a bit. Best recovery zone should be west of there.

[andyhb]

I'm starting to wonder whether a D2 moderate risk will be issued for tomorrow with the later D2 update this morning. Both the NAM and GFS have a favorable parameter space over a large area and the ascent from that lead impulse should be substantial enough to encourage fairly widespread initiation. Forcing is fairly diffuse too which may encourage a rather long-lived discrete mode.

[OUGrad05]

I'm starting to wonder whether a D2 moderate risk will be issued for tomorrow with the later D2 update this morning. Both the NAM and GFS have a favorable parameter space over a large area and the ascent from that lead impulse should be substantial enough to encourage fairly widespread initiation. Forcing is fairly diffuse too which may encourage a rather long-lived discrete mode.

I agree. It seems the conditions should warrant and upgrade to mdt for tomorrow along and West of I35.

Okc metro will be under the gun again.

[andyhb]

NAM is already going bonkers with STP over W OK/KS on Saturday, and even well before the usual ramp up after 00z.

 

Forecast soundings from the NAM are reminding me of 10/4/13, except over a significantly larger area of real estate.

[Smokey_mountain_vols]

NAM is already going bonkers with STP over W OK/KS on Saturday, and even well before the usual ramp up after 00z.

Forecast soundings from the NAM are reminding me of 10/4/13, except over a significantly larger area of real estate.

I wonder if Moore ever thinks "why always me" In these situations?

[andyhb]

Veer-back-veer seems to have improved on the 06z/12z GFS runs, but it still seems to be breaking out an awful lot of convection before primetime on Saturday and still refuses to appreciably increase its low level shear values.

[Ground Scouring]

Veer-back-veer seems to have improved on the 06z/12z GFS runs, but it still seems to be breaking out an awful lot of convection before primetime on Saturday and still refuses to appreciably increase its low level shear values.

Actually, I like the fact that the heaviest convection over E OK before 12Z is much less widespread/moves out more quickly on the 12Z as opposed to previous runs. Plus, the overall evolution of the trough has been to favor a more rapid ejection and a broader, more consolidated mid-level feature, thereby greatly alleviating the veer-back-veer not just before 00Z, but also well into the overnight and early morning hours. The ECMWF and the GFS now seem to be inching toward better agreement on the timing of large-scale ascent and ejection, and the overall net trend is faster and more favorable for a significant severe outbreak on Saturday--one with a potentially long-lived threat for supercells/significant tornadoes overnight. So my concerns at this point are starting to diminish. As far as low-level shear is concerned, doesn't the GFS have a low bias in these cases? To me, what matters is the overall synoptic set-up, the improving thermodynamic prospects (at least before 18Z), and the strengthening low-level jet into the evening hours/overnight. Initiation time will still need to be nailed down, but fortunately there is ample time for change. The GFS is probably suffering from convective feedback due to WAA.