Storm Development in
an Unfavorable Environment...Part II

Mark Cunningham NWSFO Jackson

 

Peter Wolf NWSO Wichita, KS

 

 

 

 

 

 

    Synoptic Composite Chart at 00 UTC on 5/15/97

     

  • Large, thick arrows are upper level jets
  • Large thin arrows is the low level jet
  • Small arrows indicate surface flow
  • The 16 degree Celcius surface dew point contour

 

 

 

 

 

    May 15, 1997, 00 UTC Jackson, MS modified sounding

     

  • Cape = 1426 JK/g
  • 500 mb LI= -6
  • K-index = 26
  • SWEAT Index= 328
  • 700-500mb lapse rate = 7.2 deg/Ckm
  • WBZ level = 10,026 ft

 

 

 

 

 

 

    May 15, 1997 00 UTC Jackson, MS hodograph

     

  • 0-3km SR Hel=33 m2/s2
  • 0-6km shear vector= 22 m/s
  • 0-1km swise vort= 5/s
  • storm motion from 281 degrees at 31 knots

 

 

 

 

 

 

 

May 15, 1997, 00 UTC, Jackson, MS modified hodographs

 

 

    Top hodograph

     

  • observed storm motion 305 degrees at 29 knots
  • 0-3km SRH=126 m2/s2

 

    Bottom hodograph

     

  • 0-3km SRH = 261 m2/s2
  • 0-6km Shr vector = 30 m/s
  • 0-1km swise vort = 32/s

 

 

 

 

 

 

    0.5 degree reflectivity at 2131Z on 5/14/97

     

  • Hail size= 2.25 in
  • Vil= 56
  • 68 DBZ to 11,000 ft
  • Cell located at azran 359 degrees at a range of 57 nm or over northern Holmes county.

 

 

 

 

 

 

    0.5 degree reflectivity at 2152Z

     

  • Hail size > 3.00 in
  • Vil = 63
  • 69 DBZ at 10,000 ft
  • cell located at azran 5 deg at range 52 nm or over northeast Holmes county

 

 

 

 

 

 

Cell has a bounded weak echo region and greater than 65 DBZ up to 26,000 ft

 

 

 

 

 

 

    0.5 degree storm relative velocity at 2212Z

     

  • Cell has a defined TLS
  • TLS has a base of 4000 ft and a top of 23,000 ft
  • Max low altitude gate to gate rotational velocity is 32 knots

 

 

 

 

 

 

    0.5 deg reflectivity at 2217Z

     

  • Cell has a hook
  • Hail size > 3.00 in
  • Vil = 59
  • 72 DBZ at 18,000 ft
  • Cell located at azran 19 degrees at a range of 47 nm or over western Attala county

 

 

 

 

 

 

    0.5 degree reflectivity at 2232Z

     

  • Hail size = 3.00 in
  • Vil = 55
  • 70 DBZ at 18000 ft
  • Cell located at azran 29 degrees at a range of 46 nm or over Attala county

 

 

 

 

 

 

    Time-height series plot of rotational velocity

     

  • Height is from 2 km to 9 km
  • Time is from 2132Z to 2232Z
  • A thin 12m/s contour is drawn
  • Bold numbers indicate rotational velocities greater than 15m/s

 

 

 

Conclusion

 

  • On May 14, 1997 a thunderstorm became supercellular as it tracked southeast along an apparent outflow boundary produced by organized convection to the east.
  • As this cell interacted with the boundary, strong horizontal streamwise vorticity was ingested into the updraft, leading to the formation of a strong low level mesocyclone.
  • KJAN WSR 88-D indicated supercell signatures, including a bounded weak echo region, strong low level mesocyclone, and low level hook echo in the reflectivity pattern.

     

     

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