May 15th - 20th Plains Storm/Severe disco

[baroclinic_instability]

Thread for the first plains-wide severe threat. Lots of question marks remain, however, including capping near the dryline, speed/placement of trough ejection, wave tilt (EC/UK depicting a slower/deeper neg tilt wave) elevated DMC farther N near the WF, etc. Boundary layer moisture return is not going to be a problem, however.

[wxmeddler]

   DAY 4-8 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0344 AM CDT MON MAY 13 2013
   
   VALID 161200Z - 211200Z
   
   ...DISCUSSION...
   FOCUS FOR WIDESPREAD SEVERE WEATHER REMAINS ACROSS THE CENTRAL
   PORTION OF THE U.S. FOR LATE THIS WEEK /FRI. THROUGH SUN. MAY
   17-19/...AS A WRN U.S. TROUGH PROGRESSES EWD INTO THE PLAINS.
   
   THE GFS AND ECMWF CONTINUE TO DIFFER WITH RESPECT TO THE EJECTION OF
   THIS FEATURE...WITH DIFFERENCES BETWEEN THE MODELS GRADUALLY
   INCREASING WITH TIME.  STILL...A CONSISTENT SIGNAL FOR CENTRAL U.S.
   SEVERE WEATHER HAS BEEN HINTED AT FOR SEVERAL DAYS...WITH CURRENT
   INDICATIONS THAT THE GREATEST THREAT MAY EXIST BEGINNING DAY 6 /SAT.
   5-18/.  WHILE THE GFS HINTS AT SOME POTENTIAL FOR DAY 5/FRIDAY --
   PARTICULARLY ACROSS THE NRN PLAINS VICINITY...THE SLOWER ECMWF
   MAINTAINS RIDGING ACROSS THE PLAINS DAY 5.  THUS...FOCUS THIS
   FORECAST WILL BE ON DAY 6...WITH THE ZONE OF OVERLAP OF THE TWO
   MODEL SOLUTIONS EXISTING ACROSS THE CENTRAL PLAINS VICINITY.  WITH
   STRONG INSTABILITY EXPECTED AND SHEAR LIKELY SUPPORTIVE OF
   SUPERCELLS...LARGE HAIL AND DAMAGING WINDS WILL BE POSSIBLE...ALONG
   WITH SOME TORNADO RISK.
   
   ADDITIONAL SEVERE POTENTIAL WOULD LIKELY PERSIST -- THOUGH FARTHER E
   -- FOR DAY 7/SUNDAY...BUT WITH DIFFERENCES IN MODEL SOLUTIONS
   INCREASING AND WITH LIKELIHOOD FOR WIDESPREAD CONVECTION DAY 6
   INFLUENCING DAY 7 CONVECTIVE POTENTIAL...WILL REFRAIN ATTM FROM ANY
   AREAL ISSUANCE BEYOND DAY 6.
   
   ..GOSS.. 05/13/2013

 

[andyhb]

For reference in terms of area, that risk is around as large as the D6 issued for 4/14 last year.

[jojo762]

For reference in terms of area, that risk is around as large as the D6 issued for 4/14 last year.

4-14 hmmm.... Wouldn't that be nice to see again, a tornado producing factory. Probably won't get that this time, but who knows.

[Chrisrotary12]

Someone mentioned this in the other pinned thread.  About there not being a beastly cap in South Dakota on Friday.  

 

Any chance the lack of a cap screws us over?

[brettjrob]

Someone mentioned this in the other pinned thread.  About there not being a beastly cap in South Dakota on Friday.  

 

Any chance the lack of a cap screws us over?

 

In this low-amplitude pattern, I'd be much more worried about the cap than lack of one, as a general rule. If the timing of an embedded shortwave proves ill-timed on any given day, the result is usually veered low-level flow, which advects horrendously hot air around H85-H7 over the dryline. It's tough to envision a scenario either Fri/Sat where a bust results from too many storms in close proximity, but then we are still 4-5 days out, so it's possible.

[ZackH]

The GFS verbatim has a very breakable cap on Friday in the SD if there is enough forcing, but as Brett somewhat eluded to, this far out those details are not handled well in the models.  That's probably something we won't get a great handle on until a day or two before.

[HM]

The 5/12 12z GFS run was a clear outlier against the ensemble mean by being faster/less amplified. However, from the 5/12 18z run through this morning's 6z run, it was nestled nicely if not more amplified and slower than the ensemble members. Today's 12z run continues to slow down a bit and grow more amplified. We may possibly see the ECMWF and GFS converge on a solution today with regards to Saturday's evolution.  

[Ian]

The 5/12 12z GFS run was a clear outlier against the ensemble mean by being faster/less amplified. However, from the 5/12 18z run through this morning's 6z run, it was nestled nicely if not more amplified and slower than the ensemble members. Today's 12z run continues to slow down a bit and grow more amplified. We may possibly see the ECMWF and GFS converge on a solution today with regards to Saturday's evolution.

Yeah noticed it looked slower.. On phone so not sure how much. Good news for us.

[Derek30]

The 5/12 12z GFS run was a clear outlier against the ensemble mean by being faster/less amplified. However, from the 5/12 18z run through this morning's 6z run, it was nestled nicely if not more amplified and slower than the ensemble members. Today's 12z run continues to slow down a bit and grow more amplified. We may possibly see the ECMWF and GFS converge on a solution today with regards to Saturday's evolution.  

Heck, the 12z GFS has 60+ dews all the way up into far southern MB. Not sure if I buy that quite yet.

[andyhb]

4-14 hmmm.... Wouldn't that be nice to see again, a tornado producing factory. Probably won't get that this time, but who knows.

 

That was a completely different synoptic setup to this one, that was just a comparison of the outlook area.

[HM]

Yeah noticed it looked slower.. On phone so not sure how much. Good news for us.

 

 

Heck, the 12z GFS has 60+ dews all the way up into far southern MB. Not sure if I buy that quite yet.

 

The 12z GGEM and UKMET are also more amplified, closing things off sooner and going negatively tilted sooner (slower than GFS).

[Ian]

That was a completely different setup to this one, that was just a comparison of the outlook area.

Sat looks like a mod as is tho maybe I'm weenieing. I just want to have a sun play too which the GFS does well.

[andyhb]

The 12z GGEM and UKMET are also more amplified, closing things off sooner and going negatively tilted sooner (slower than GFS).

 

I also noticed with the 12z suite so far that the UL jet on the days after Saturday has more of a tendency to eject out of the bottom of the trough (in a westerly/west-northwesterly heading), which would decrease backing in the upper levels and improve the vertical wind profile for Sunday/etc.

[HM]

The one thing I keep seeing run to run is the amazing upper level jet structure and divergence on Saturday. The divergence aid from two different streaks right over OK-KS-NE is pretty sick, regardless of the smaller details right now.

[KSWx]

Anyone else thinking the models are showing western/central Kansas to have more potential than further east? My parents live in the dead center of Kansas so I'm thinking I might stay out there Friday night as opposed to staying out east. I know it's fairly early to tell for sure but I'm getting giddy.

[andyhb]

The Euro is still stubbornly coming in less amplified on Saturday, ala the 12z run yesterday. It actually looks quite nice at 96, but flattens out after that (which leads to a veering LLJ).

 

The upstream ridging in behind is clearly not as amplified as on the 12z GFS/GGEM.

[Ian]

The Euro is still stubbornly coming in less amplified on Saturday, ala the 12z run yesterday.

 

The upstream ridging in behind is clearly not as amplified as on the 12z GFS/GGEM.

 

It and the GFS like to switch places potentialwise. 

 

Given the euro ens looked solid last night... well, I'd wait for that.

[Dsnowx53]

The Euro is still stubbornly coming in less amplified on Saturday, ala the 12z run yesterday. It actually looks quite nice at 96, but flattens out after that (which leads to a veering LLJ).

 

The upstream ridging in behind is clearly not as amplified as on the 12z GFS/GGEM.

 

 

The one thing the Euro has been consistent on is not having nearly as much upstream ridging as the other guidance does. 

 

Edit: That being said, however, its upstream ridging increases as the system amplifies and moves east. That's actually a bit of a shift towards the GFS. 

[andyhb]

I'd imagine there's some sort of setup in the Mid MS Valley region around 180 hrs with that second vort max rotating around the base of the ULL, which induces a sfc cyclone that rockets from the Plains to the Central Great Lakes region in 24 hours.

[Amped]

12z Euro also looks good in the sun-tue timeframe and continues the outbreak into the great lakes ov.

[wx_chip]

Really wouldn't mind if the system would just crash into a more amplified ridge over the East Coast and keep that warm sector a bit stronger in the central Plains. Take this event and keep it active in the Plains through early next week... the more the models slow, the better chance it will have to strengthen that ridge.

[andyhb]

Really wouldn't mind if the system would just crash into a more amplified ridge over the East Coast and keep that warm sector a bit stronger in the central Plains. Take this event and keep it active in the Plains through early next week... the more the models slow, the better chance it will have to strengthen that ridge.

 

Which ridge are you referring to? The one that Dsnow and I were referring to is the one in behind this system in the Eastern Pacific.

[HM]

The ECMWF suggests that the second wave crashing into the PAC NW will prevent a total closed low / wrapped up scenario (something like the GGEM e.g.) from happening over the NW/High Plains. This seems to be one of those situations where the blocking may not help you pick a camp; rather, only teleconnect on a large scale of having a l/wv feature over the West. The embedded s/w will not be ironed out probably until really close. Convective processes will affect these by the way.

[Ian]

Euro ens mean looks better than the op for Sat.. at least a bit. Plus it doesn't bog down the low in the lakes.. got that dual trough thing going most of the run.

[HM]

Euro ens mean looks better than the op for Sat.. at least a bit. Plus it doesn't bog down the low in the lakes.. got that dual trough thing going most of the run.

I wish I could see the individual members of the EPS to rule out smoothing. Having said that, I agree with you. Hands down, the best 200mb structure is on the op GFS.

[ZackH]

Not a huge fan of the 18z GFS... hopefully its just an anomaly.  Best instability is not collocated with the more impressive shear.

[jojo762]

That was a completely different synoptic setup to this one, that was just a comparison of the outlook area.

I know what ya meant, I was just saying it would be awesome to see an outbreak that produces 100+ tornadoes. And was saying that we really don't have a chance of that happening this time.

[andyhb]

I know what ya meant, I was just saying it would be awesome to see an outbreak that produces 100+ tornadoes. And was saying that we really don't have a chance of that happening this time.

 

If that's what is going to meet your expectations, then you are going to be disappointed a lot.

[ZackH]

I'd be just dandy with an outbreak of 10+ photogenic tornadoes that I can get to.  Actually if there's only one and its photogenic and I'm there, I'm fine with that... and no matter how many there are, I hope they are all over open fields.