Significant Severe Events: June 14th-19th

[andyhb]

There's no D4-8 outlook area yet, but I thought I'd get a thread started on what looks to be a rather favorable pattern for a lengthy duration of severe potential from this weekend extending into the middle of next week.

 

First off is a shortwave trough/ULL that looks to eject this Saturday from the central/northern Plains into the Upper Midwest. The instability axis on Saturday through the central Plains looks to be displaced from the best shear so it doesn't look to have a very high ceiling (although the 00z GFS did raise an eyebrow). Sunday looks to have MCS potential from whatever develops on Saturday and possible new development throughout the day.

 

The potential for more serious fireworks comes with the pattern afterward. The GFS has been pretty shoddy run to run so until it shows better continuity, I'm not really taking it into account much for this. The Euro/GGEM/UK trio have been indicating for several runs in a row now that a pretty large/broad longwave trough will open up in the West towards the beginning of next week, with the possibility of multiple shortwave troughs ejecting into the Plains/Midwest. On top of that, a large pool of very high instability (owing to an excess of moisture being fed from deep in the Caribbean and even the tropical Atlantic) appears to be in place for these s/w ejections. There still appears to be considerable spread amongst the ensemble means about how this will evolve (which is also modulated by how the lead trough on Sat/Sun develops eastward), but generally an active jet like this in June with the instability being shown across the suite will lead to something.

 

Most recent D4-8 outlook, mostly touches on Sat/Sun, and leaves the rest.

 

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0344 AM CDT WED JUN 11 2014

VALID 141200Z - 191200Z

...DISCUSSION...
MEDIUM RANGE GUIDANCE IS IN FAIRLY GOOD AGREEMENT THROUGH DAY
5/SUNDAY. ON SATURDAY...A SHORTWAVE TROUGH ROTATING THROUGH
LARGER-SCALE MEAN TROUGH OVER THE WEST WILL TRACK ACROSS THE
NORTHERN PLAINS. A SFC LOW WILL INTENSIFY AND LIFT E/NE FROM SD
TOWARD NRN MN...WITH A DRYLINE/COLD FRONT EXTENDING S/SWWD THROUGH
THE CNTRL/SRN PLAINS. WIDESPREAD THUNDERSTORMS ARE EXPECTED BOTH
ALONG THE COLD FRONT DURING THE LATE AFTERNOON/EVENING OVER THE
NRN/CNTRL PLAINS AND IN WAA REGIME NEAR THE WARM FRONT OVER ND/MN.
ONE OR MORE MCS/S MAY DEVELOP FROM THIS AFTERNOON CONVECTION AND
TRACK EWD OVERNIGHT ACROSS THE MID/UPPER MS AND MID-MO VALLEYS. ON
SUNDAY...THE SHORTWAVE TROUGH WILL CONTINUE EWD THROUGH THE UPPER
MIDWEST AND GREAT LAKES IN CONJUNCTION WITH THE SFC LOW. THIS WILL
BRING A COLD FRONT THROUGH THE UPPER MS VALLEY INTO THE CNTRL
PLAINS...ONCE AGAIN SERVING AS FOCUS FOR THUNDERSTORMS DURING THE
AFTERNOON INTO THE OVERNIGHT...AND MCS DEVELOPMENT WILL ONCE AGAIN
BE POSSIBLE ACROSS PARTS OF THE MID/UPPER MS VALLEY INTO THE OH
VALLEY. WHILE GUIDANCE IS IN GENERAL AGREEMENT OVER THIS
SCENARIO...DIFFERENCES EXIST IN THE PLACEMENT OF THE SFC LOW AND IN
THE PLACEMENT OF STRONGER MIDLEVEL FLOW. ALTHOUGH SEVERE CONVECTION
IS EXPECTED DURING THE WEEKEND FROM EASTERN PORTION OF THE NRN/CNTRL
PLAINS INTO THE MID/UPPER MS VALLEY...CONFIDENCE IS LOW WHERE
EXACTLY THIS WILL OCCUR AND EVOLVE DUE TO THE AFOREMENTIONED MODEL
DISPARITIES.

BY DAY 6...GUIDANCE BEGINS TO DIVERGE QUITE A BIT WITH LARGE PHASING
ERRORS IN THE EVOLUTION OF THE WESTERN TROUGH/EASTERN
RIDGE...LEADING TO LOW CONFIDENCE IN SEVERE POTENTIAL LATER IN THE
FORECAST PERIOD.

..LEITMAN.. 06/11/2014

[Thundersnow12]

Saturday looks absolutely awesome on the 12z GFS. 

 

First thought was 4/14/12 and no I'm not calling for a big outbreak and I know the trof shape was different but looking at the N/S orientation of the dryline. Actually looks to have better directional shear with a more westerly component in model land compared to that day. 

[andyhb]

 The instability axis on Saturday through the central Plains looks to be displaced from the best shear so it doesn't look to have a very high ceiling (although the 00z GFS did raise an eyebrow).

 

Scratch that if the 12z GFS is on the right track.

 

Also, it has a another powerful trough across the northern Plains pre-truncation.

 

12z Euro kind of goes to crap after the first trough, there's not enough ridge amplification for the second trough to develop properly. However, it also puts out a string of pearls on the dryline in NE on Saturday within an explosive looking environment.

[bdgwx]

Comments on the 12Z ECMWF? It is initiating convection along the dryline Saturday evening. 0-6 km shear is generally < 40 kts, but most of that is in the lowest 1 km with winds significantly backed. There is definitely plenty of instability to work with.

[Thunder Road]

I'm probably going to target Sioux Falls Saturday.  Haha

 

The guy I went out with last time is in Brazil for the World Cup, so if it continues to look good and someone wants to tag along, PM me.

 

I've been downplaying it, but the 12z GFS looked better, even up here (although any farther east and you're capped).  It was throwing out 0-1 km bulk shear of around 15-20 kts up here, which is sufficient.  And bases look like they'll be plenty low enough too. (maybe even too low?)

 

I still have concerns though.  It's another setup with a narrow sector where things are primed.  Too far east and you're capped, too far west and you're outside of the LLJ.  And it still looks like the boundary will be playing catch-up to the LLJ up here, which raises the question of storm mode, since low-level shear will probably be less than ideal at initiation.

 

Nonetheless, something to watch!

[andyhb]

I'm quite surprised by the small/low probability D3 outlook, despite the uncertainties, both the Euro and GFS have some really robust looking parameters setting up across the Central Plains including an unseasonably strong LLJ, strong/well developed leeside cyclogenesis, breakable cap, rather broad axis of strong instability becoming better co-located with the LLJ axis with each run, etc.

 

In addition to that, this trough screams supercells as the dominant mode given its broad base and adequate mid/upper level flow spreading well out ahead of the main trough axis. The 00z Euro reminds me a bit of 5/29/04 shifted north (mainly looking at 500 mb, 850 mb and the surface here). The 500 mb flow over the Plains that day actually wasn't exceptionally strong, generally in the 40-50 kt range, which looks to be attainable here.

 

 

Honestly a lot of other June Plains setups would blush at what the general model consensus is for Saturday. While it might not be saying much, it looks like the best setup for the Plains we've seen all year.

[andyhb]

Meanwhile, the entire model suite has gone to absolute la-la land on what happens afterward, with four completely different solutions among the 00z Euro, GFS, UK and GGEM (and equal madness among the ensembles), pretty much the definition of a crapshoot at this juncture.

[brettjrob]

I'm quite surprised by the small/low probability D3 outlook, despite the uncertainties, both the Euro and GFS have some really robust looking parameters setting up across the Central Plains including an unseasonably strong LLJ, strong/well developed leeside cyclogenesis, breakable cap, rather broad axis of strong instability becoming better co-located with the LLJ axis with each run, etc.

 

In addition to that, this trough screams supercells as the dominant mode given its broad base and adequate mid/upper level flow spreading well out ahead of the main trough axis. The 00z Euro reminds me a bit of 5/29/04 shifted north (mainly looking at 500 mb, 850 mb and the surface here). The 500 mb flow over the Plains that day actually wasn't exceptionally strong, generally in the 40-50 kt range, which looks to be attainable here.

 

Honestly a lot of other June Plains setups would blush at what the general model consensus is for Saturday. While it might not be saying much, it looks like the best setup for the Plains we've seen all year.

 

Even setting aside my 2014 bias, this is a tough one to crack. I also thought 5/29/04 almost immediately upon looking at the H5 forecast a few days ago. Right now, I'd say the one glaring difference is that we're looking at a somewhat more positive-tilt trough, and the H25 jet streak is much farther north (relative to surface features). Add in the Southwest drought, and IMHO, this signifies much bigger capping issues down the dryline. I have a hard time envisioning a full-fledged outbreak down the dryline in S/C KS or OK, for example.

 

For N KS and S NE, though, it sure looks like a powder keg. Even there, the cap makes me nervous, but a large portion of the modeling has convective signals. I agree that from this stage, the probability of a significantly-tornadic supercell with this setup looks better than most have this year, little as that's saying. I think the biggest question for chasers will be HP vs. classic.

[andyhb]

I have a hard time envisioning a full-fledged outbreak down the dryline in S/C KS or OK, for example.

 

Oh yeah, I agree with this. The main threat is going to be in NE (again) and vicinity. I do like how we're not focusing on a warm front for initiation for the umpteenth time.

 

5/29/04 wasn't widespread further south either to be fair, but you had two supercells become tornado producing machines across south central KS (Attica pt. II/Argonia/Conway Springs) and central OK. The KS one produced some of the most photogenic tornadoes I've ever seen.

[Thunder Road]

Looking at the 12z NAM, this has the makings of a sleeper setup.  And as andy said, for once a good set-up not on a warm front!

 

I already like the triple point in south central NE.  But pay close attention to the surface temp field at 21z.  It looks like there's a second subtle warm front running up from SE KS into the triple point.  Trace the surface wind vectors back and you see the difference is between air being advected straight up from the Gulf and air coming in from the Southeast, over land longer.  

 

The NAM has that boundary intersecting the N-S boundary right at the triple point.  You can see this in 0-1 km helicity, which is maximized right at that intersection, as there's probably a little bit of backing right there.  If this signal is persistent, it would probably have me making a bee line for Grand Island.

 

Not too worried about capping north of the NE/KS border.  Yes, there is a cap (h7 temps around 13 C at their warmest) but it looks breakable.  Or at least, the NAM thinks so.  It convects all of eastern NE after 21z, and you can even see it trying to resolve individual cells/reflectivity maxima.  The GFS has had a precip signal for several runs too.

[andyhb]

Holy moly at the convective signal in NE on the 12z Euro by 03z Sunday.

[MCS_hunter]

Holy moly at the convective signal in NE on the 12z Euro by 03z Sunday.

The NAM's sig tor parameter really ramps up at this time too along with a line of convection on the simulated reflectivity.

[Chinook]

Looking at the 12z NAM, this has the makings of a sleeper setup.  And as andy said, for once a good set-up not on a warm front!

 

I already like the triple point in south central NE.  But pay close attention to the surface temp field at 21z.  It looks like there's a second subtle warm front running up from SE KS into the triple point.  Trace the surface wind vectors back and you see the difference is between air being advected straight up from the Gulf and air coming in from the Southeast, over land longer.  

 

The NAM has that boundary intersecting the N-S boundary right at the triple point.  You can see this in 0-1 km helicity, which is maximized right at that intersection, as there's probably a little bit of backing right there.  If this signal is persistent, it would probably have me making a bee line for Grand Island.

 

Not too worried about capping north of the NE/KS border.  Yes, there is a cap (h7 temps around 13 C at their warmest) but it looks breakable.  Or at least, the NAM thinks so.  It convects all of eastern NE after 21z, and you can even see it trying to resolve individual cells/reflectivity maxima.  The GFS has had a precip signal for several runs too.

 

3500 J/kg of CAPE and 40 kts of shear is a sleeper?  Looks like a big sign saying, "chasers travel here."  (12z NAM @ 57 hours)

[andyhb]

3500 J/kg of CAPE and 40 kts of shear is a sleeper?  Looks like a big sign saying, "chasers travel here."  (12z NAM @ 57 hours)

 

I think he means the fact that this was pretty much nothing on the models 2 days ago.

[Thunder Road]

3500 J/kg of CAPE and 40 kts of shear is a sleeper?  Looks like a big sign saying, "chasers travel here."  (12z NAM @ 57 hours)

 

 

I think he means the fact that this was pretty much nothing on the models 2 days ago.

 

Yeah.

 

Not that it'll be a day-of surprise, but that until last night I wasn't excited about it at all, and now today I'm mapping out travel times to cities in Nebraska, haha.

[brettjrob]

12z ECMWF looks fantastic for much of the southeastern half of NE. CIPS analog guidance has consistently matched a slew of events with tornado reports near and along the Hastings-Omaha corridor, and I'm beginning to think that Saturday will fit right in with those.

[Jayhawkers]

Dang, if any storms were to initiate further south in Kansas on saturday, they could go absolutely nuts as well, and last well into the overnight hours, and would have the potential to produce some tornadoes... Environment really lights up on the NAM after 00Z on saturday, with widespread 0-1KM EHI's of 3+ and widespread 0-3KM EHI's of 6-12... All being produced by 0-1KM SRH of 200-300m2/s2 and 0-3KM SRH of 500-700m2/s2. Combined with sfc-500mb SHR of 40-65kts and LLVL SHR of 30-40kts... But instability appears to  diminish after 03Z so maybe not a prolonged night threat, but still something to pay attention too imo. Cap is obviously pretty strong, but if any storms did form it would be quite a show. Besides central KS, Nebraska looks like a much safer bet to see convection that would be just as intense, if not more.Thoughts? FWIW: NAM has been fairly consistent showing this scenario so figured i'd just throw this in to the convo. Also the environment it depicts along the KS/NE border on saturday for much of the day is nuts.

[Quincy]

Beyond Saturday, the 12z Euro is looking fairly active for Mon-Wed as well. Each day features a fairly large area with >4500 SBCAPE with decent wind fields. Slow-moving trough moves into the Rockies as a surface low ejects from eastern CO into the Dakotas. The models have not been in the best agreement, but I would have to imagine at least one or two days next week could feature good severe potential as well.

[Thunder Road]

I'm not crazy with how the 0z NAM handles Saturday.  CIN is gone by 21z with convection going up in eastern NE, ahead of the front.  Then at 0z that stuff all has died and new convection on the front is forming, while CIN is back up to 100 J/kg or more.  Just seems kinda weird.

[andyhb]

I'm not crazy with how the 0z NAM handles Saturday.  CIN is gone by 21z with convection going up in eastern NE, ahead of the front.  Then at 0z that stuff all has died and new convection on the front is forming, while CIN is back up to 100 J/kg or more.  Just seems kinda weird.

The NAM has been really poor with both synoptic and mesoscale features as of late (or more like the entire year).

[brettjrob]

Not overly worried about the NAM/BMJ convective output right now, but I am concerned that both NAM and GFS soundings increasingly point toward the dreaded H7 kink, i.e. "S-shaped" hodographs in the low-levels. Aside from that, surface winds will need to back more than progged for a widespread tornado threat to materialize. They probably will to some extent, though. Anyhow, both the S-shape and the potential for moisture to underperform a bit -- and the resultant cap implications -- are worries I have at this stage.

[Thundersnow12]

IMO, IA looks much better on Monday on the new GFS than how Saturday is looking

[tornadotony]

The GFS looks just fine on Saturday in ern NE.  And given how the NAM has performed lately, I'd take that as an encouraging sign.

[tornadotony]

IMO, IA looks much better on Monday on the new GFS than how Saturday is looking

No.  I don't buy IA being much better than just about anything so long as we're analyzing a warm frontal situation.  There could be a decent event, but if we're comparing apples to apples (GFS progs) instead of apples to cow manure (GFS to NAM), then Saturday looks better in ern NE than Monday in IA.

[Quincy]

The GFS looks just fine on Saturday in ern NE. And given how the NAM has performed lately, I'd take that as an encouraging sign.

Even using NAM-based analogs, the signal is fairly strong. More than half of the analogs featured 10 or more severe reports in eastern NE. The most severe analogs suggest a 75% probability of a severe report (SPC equivalent) over eastern NE with tornado probs maxing out at 15% near the eastern NE/KS border. Probs for significant/widespread tornadoes are on the lower end though.

[Thunder Road]

Wow.  D2 Moderate.  Was only expecting a 30 hatched.

[Jayhawkers]

That escalated quickly from D3 low-end, low-confidence SLGT risk to D2 "high-confidence" MDT risk. Mentioned "giant" hail lol, whatever the threshold is for that...

[Thunder Road]

That escalated quickly from D3 low-end, low-confidence SLGT risk to D2 "high-confidence" MDT risk. Mentioned "giant" hail lol, whatever the threshold is for that...

 

I believe 4.0"

[Jayhawkers]

I believe 4.0"

literally? I wasn't aware that there was an actual diameter threshold for giant hail. Lol. Only seen that mentioned by the SPC a few times...

[andyhb]

IMO, IA looks much better on Monday on the new GFS than how Saturday is looking

 

The mid level height rises the GFS is showing on Monday probably wouldn't be good for initiation especially within that really impressive environment in IA.