2 replies to this topic

[Mike Puckett]

Didn't see a discussion about this 1 sooooooo here ya go  



SEVERE WEATHER EVENT WITH TORNADOES AND VERY LARGE HAIL APPEARS
   LIKELY ACROSS THE NRN PLAINS AND UPPER MS VALLEY THIS AFTERNOON INTO
   TONIGHT...
  
   ...NRN PLAINS/UPPER MS VALLEY...
   ZONAL WLY FLOW WILL EXIST ACROSS THE NCNTRL STATES TODAY AS THE EXIT
   REGION OF A MID-LEVEL JET MOVES INTO THE REGION FROM THE WEST. THIS
   FEATURE WILL HELP CREATE STRONG DEEP LAYER SHEAR PROFILES FAVORABLE
   FOR SEVERE STORMS. AT THE SFC...A LOW IS FORECAST TO DEEPEN ACROSS
   ECNTRL SD WITH A CORRIDOR OF LOW-LEVEL MOISTURE EXTENDING FROM THE
   MID-MO VALLEY NWD INTO ERN SD AND SW MN BY LATE AFTERNOON. SFC
   DEWPOINTS APPEAR LIKELY TO REACH THE MID TO UPPER 60S F WITH
   MODERATE TO STRONG INSTABILITY IN PLACE BY AFTERNOON ACROSS THE WARM
   SECTOR. THE MODELS ARE IN GENERALLY GOOD AGREEMENT DEVELOPING
   THUNDERSTORMS IN ERN SD AND MOVING AN CLUSTER OF STRONG CONVECTION
   EWD ACROSS SRN MN THIS EVENING.
  
   FORECAST SOUNDINGS AT 00Z/MON IN ERN SD SHOW MLCAPE FROM 2500 TO
   3000 J/KG WITH AN IMPRESSIVE SHEAR ENVIRONMENT. 0-6 KM SHEAR IS
   FORECAST TO INCREASE DURING THE DAY REACHING 50 TO 55 KT BY EARLY
   EVENING. THIS ALONG WITH A STRENGTHENING 40 TO 50 KT LOW-LEVEL JET
   SHOULD BE FAVORABLE FOR TORNADIC SUPERCELLS. FORECAST SOUNDINGS NEAR
   AND JUST EAST OF ABERDEEN AT 00Z/MON SHOW 0-3 KM STORM RELATIVE
   HELICITIES OF 350 TO 400 M2/S2 WITH LCL HEIGHTS AROUND 700 METERS
   SUGGESTING A THREAT FOR STRONG TORNADOES WILL BE POSSIBLE. IN
   ADDITION...SUPERCELLS SHOULD CONTAIN LARGE HAIL WITH HAIL GREATER
   THAN 2 INCHES IN DIAMETER POSSIBLE WITH THE MORE DOMINANT ROTATING
   STORMS. AS STORM COVERAGE INCREASES DURING THE EVENT...A LINE OF
   STORMS COULD ORGANIZE ACROSS SRN MN WITH DISCRETE ROTATING CELLS
   EMBEDDED IN THE LINE. THE STRONG SHEAR AND WELL-DEVELOPED LOW-LEVEL
   JET SHOULD HELP THE TORNADO THREAT TO CONTINUE INTO THE EVENING.
   HOWEVER...A GRADUAL TRANSITION TO A WIND DAMAGE THREAT SHOULD TAKE
   PLACE DURING THE EARLY TO MID EVENING. THE LINE COULD MOVE ESEWD
   INTO CNTRL AND ERN IA BY LATE IN THE EVENING. THE SEVERE THREAT
   SHOULD DROP OFF QUICKLY TO THE SOUTHWEST OF THE MCS MAINLY DUE TO
   WARMING MID-LEVEL TEMPS.
  
   ...LOWER GREAT LAKES/UPPER OH VALLEY...
   A SHORTWAVE TROUGH IS FORECAST TO MOVE ACROSS THE GREAT LAKES REGION
   TODAY. AHEAD OF THE SHORTWAVE TROUGH...AN AXIS OF MODERATE
   INSTABILITY SHOULD DEVELOP FROM THE OH VALLEY NEWD INTO THE LOWER
   GREAT LAKES. THUNDERSTORM DEVELOPMENT SHOULD OCCUR ALONG THE
   INSTABILITY AXIS THIS AFTERNOON AS SFC TEMPS WARM. FORECAST
   SOUNDINGS NEAR CLEVELAND AND CINCINNATI THIS AFTERNOON SHOW MLCAPE
   VALUES AROUND 2000 J/KG WITH 20 TO 25 KT OF LOW-LEVEL FLOW. THIS
   ALONG WITH STEEP LOW-LEVEL LAPSE RATES COULD BE SUFFICIENT FOR
   MARGINALLY SEVERE WIND GUSTS WITH THE STRONGER CELLS LATE THIS
   AFTERNOON.
  
   ...SRN PLAINS...
   MODERATE TO STRONG INSTABILITY IS SHOULD BE IN PLACE THIS AFTERNOON
   ACROSS MUCH OF THE SRN PLAINS WHERE THE MODELS DEVELOP SCATTERED
   THUNDERSTORMS. ALTHOUGH DEEP LAYER SHEAR IS FORECAST TO BE AT OR
   BELOW 30 KT ACROSS MUCH OF THE WARM SECTOR...STEEP LOW-LEVEL LAPSE
   RATES AND SFC DEWPOINTS IN THE MID 60S F MAY BE ENOUGH FOR A
   MARGINAL WIND DAMAGE THREAT WITH THE STRONGER UPDRAFTS. HAIL MAY
   ALSO OCCUR IN AREAS WHERE CONVECTION HAS ACCESS TO MAXIMIZED
   INSTABILITY.



I think I'd be pretty dang scared right about now if I was over there how bout you?

Edited by Mike Puckett, 17 June 2012 - 02:12 AM.

[andyhb]

The 4 km NAM blows up a line of discrete supercells in that general area around 22z, keeps them discrete for at least 3 hrs, before merging them into an intense complex that propagates eastward, as the outlook suggests. The thing this has going for it is definitely the LCL heights, which look to be quite favorable for potentially significant/large tornado action should this play out. Capping looks less than impressive, so initiation shouldn't be too difficult to achieve in the presence of average mid level temps and associated EML strength for this time of year.

Considering the magnitude of the deep layer shear, strong low level shear and a favorable thermodynamic environment, there is certainly a possibility of a regional tornado outbreak this evening across the locations highlighted within the MDT risk.

Caveats to watch for would be dewpoint mixing (which has screwed up several setups in this area this year), the possibility that the models are underestimating sfc temps, leading to higher dewpoint depressions and accordingly higher LCL heights, as well as possible EML inhibition (if mid level temps turn out higher than forecasted).

Looking at forecast soundings within the MDT risk area, hodographs certainly look nice, with a strongly curved low level vector and substantial length to it between 0 and 3 km as well, with strong veering with height and no veer-back-veer nonsense thanks to the westerly to even west-northwesterly mid/upper level winds. Hopefully people in the area are keeping tabs on the situation, given that there will probably be many outside celebrating Father's Day.

[ZackH]

andyhb, on 17 June 2012 - 02:42 AM, said:

The 4 km NAM blows up a line of discrete supercells in that general area around 22z, keeps them discrete for at least 3 hrs, before merging them into an intense complex that propagates eastward, as the outlook suggests. The thing this has going for it is definitely the LCL heights, which look to be quite favorable for potentially significant/large tornado action should this play out. Capping looks less than impressive, so initiation shouldn't be too difficult to achieve in the presence of average mid level temps and associated EML strength for this time of year.

Considering the magnitude of the deep layer shear, strong low level shear and a favorable thermodynamic environment, there is certainly a possibility of a regional tornado outbreak this evening across the locations highlighted within the MDT risk.

Caveats to watch for would be dewpoint mixing (which has screwed up several setups in this area this year), the possibility that the models are underestimating sfc temps, leading to higher dewpoint depressions and accordingly higher LCL heights, as well as possible EML inhibition (if mid level temps turn out higher than forecasted).

Looking at forecast soundings within the MDT risk area, hodographs certainly look nice, with a strongly curved low level vector and substantial length to it between 0 and 3 km as well, with strong veering with height and no veer-back-veer nonsense thanks to the westerly to even west-northwesterly mid/upper level winds. Hopefully people in the area are keeping tabs on the situation, given that there will probably be many outside celebrating Father's Day.

Some definite tornadoes have touched down and with the significant wind this MCS will put up along with the monster hail from the storms when they were still discrete/semi-discrete the moderate could still end up verifying... but this setup could have been much worse.  I actually think the lack of a decent cap (at least near the warm front) is what did this in.  Convection started firing too early and became a convective mess very quickly allowing it to start the transition into an MCS sooner than they originally anticipated.  This still has been a fun event to follow.

Edited by ZackH, 17 June 2012 - 08:52 PM.