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4/18/06 FCST: IA/MO/IL/AR/TX

Updated 2100Z image rectified for severe distortion from GOES-WEST.

Tim

18apr21z.jpg
 
It's nice to see a 21z sounding from KSGF --> http://www.spc.noaa.gov/exper/soundings/06041821_OBS/SGF.gif , which shows an essentially-uncapped environment (CINH negligible for surface-based parcel, weak for a mixed-layer parcel) with strong to extreme instability (observed CAPE >4500 j/kg is respectable any time of the year). I would a bit surpised to see how quickly the cap eroded between the 18z and 21z soundings. Initiation is occurring in northwestern MO right now, near the intersection of two boundaries / fronts seen on the EAX radar (cold front and dryline most probably, though the lack of surface obs between the boundaries makes that identification a little difficult). 40kt 0-6km shear observed at SGF would support supercells given the strong instability, though the weakness in the midlevel flow (25kts at 500mb) makes me think HP. At least the anvil-level flow (~200mb) is decent (60-70kts). Current visible sat imagery indicates Cu developing along the dryline, from east of Kansas City to near Springfield. The most favorable area for tornadoes, IMO, appears to be setting up near I70, with Jefferson City (south of Columbia) sitting at 90/64. LCLs are quite high, but the backed flow near I70 may enhance low-level shear to compensate a bit. Lathrop profiler showing that the vertical shear is favorable for a decent supercell and tornado threat.

Edit: CoD is showing that the 21z SGF sounding has 3100j/kg CAPE vs. the 4600 j/kg CAPE per the SPC page...
Edit2: Looking at the CoD sounding, it looks like they take some sort of mixed-layer / mean-layer parcel when computing CAPE, which makes sense since the CoD-derived CAPE compares pretty well with the SPC MLCAPE.
 
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