MD 1072 CONCERNING SEVERE POTENTIAL…WATCH LIKELY FOR PORTIONS OF CENTRAL/SOUTHERN/EASTERN KS…WESTERN MO
Mesoscale Discussion 1072
NWS Storm Prediction Center Norman OK
0345 PM CDT Sat Jun 17 2017
Areas affected...Portions of central/southern/eastern KS...western
MO
Concerning...Severe potential...Watch likely
Valid 172045Z - 172315Z
Probability of Watch Issuance...80 percent
SUMMARY...While not imminent, Weather Watch issuance will be likely
at some point later this afternoon or early this evening -- for
portions of the region. Significant severe hail and wind will be
possible. The potential for a couple of tornadoes will also exist.
DISCUSSION...Very strong to extreme instability has developed along
and south of a surface boundary analyzed from south-central IA to
near St. Joseph MO to just north of a line from Topeka to Salina.
The boundary trails farther west into western KS. Near and south of
the boundary, widespread strong insolation amid generally
lower/middle 70s dewpoints and an EML characterized by 8-9-C/km
midlevel lapse rates has resulted in MLCAPE of 4000-6500 J/kg.
Deeper vertical mixing across western parts of southern KS is
associated with a somewhat drier low-level profile and lower
buoyancy.
While these factors are yielding large conditional severe potential,
there is substantial uncertainty regarding the timing of robust
convective development. This is the result of strong capping
aloft -- perhaps related to compensating subsidence peripheral to a
long-lived, decayed MCS presently crossing the Red River into far
northeast TX. In fact, the 20Z Topeka KS special sounding indicates
substantial capping, with MLCINH around 180 J/kg, associated with a
shallow inversion around 850 mb beneath the base of the EML.
Visible satellite trends suggest that the southern periphery of
ACCAS fields are becoming slightly agitated across far northeast KS.
This could be in response to a combination of slight midlevel
cooling grazing the sloped frontal surface peripheral to a midlevel
speed maximum, and/or diurnally enhanced boundary-layer
circulations -- augmented by frontal baroclinicity -- aided by
diabatic surface-layer heating. Convection could develop in these
areas of mesoscale ascent relatively soon despite the antecedent
capping. Needless to say, observational data trends and CAM guidance
are suggesting somewhat variable signals regarding timing/locations
of convective initiation, and confidence in the timing and exact
location of intense convective development are somewhat muted.
Present indications are that supercell development could occur
across parts of central and northeast KS and into northwest and
west-central MO after 2130Z through around 0100Z -- but increasingly
more likely after 2230-2330Z. This will be aided by continued
surface heating and follow initial updraft pulsations along the zone
of convergence attendant to the boundary -- and perhaps aided by the
glancing influence of peripheral midlevel ascent. Additional
development will be likely in the drier air westward along the front
in KS.
The presence of 40-50 kt of effective shear oriented obliquely to
the initiating boundary will initially support discrete and
semi-discrete supercell structures. Very large hail -- potentially
baseball-size hail -- may accompany initial updrafts. Despite
relatively weak low-level shear -- associated with slight diurnal
veering of surface winds south of the boundary amid weak low-level
flow -- intense stretching of pre-existing vertical vorticity will
likely occur with maturing incipient updrafts interacting with the
boundary. As such, some tornado risk could exist during early stages
of convective development. The area of greatest potential for
intense supercells capable of some tornado risk and significant
severe hail will extend within a narrow corridor from around and
south of the Salina and Fort Riley areas toward Topeka and Kansas
City.
However, there should be a tendency for convection to produce
intense outflows -- given DCAPE of 1400-1800 J/kg amid the
well-mixed boundary layer -- while increasing in coverage through
the late afternoon and evening. This will likely curtail the
spatiotemporal window of opportunity for tornado potential, while
the risk for damaging straight-line winds increases. Amalgamating
cold pools will have a tendency of supporting localized clusters of
upscale convective growth as storms spread southeastward and
east-southeastward into the evening hours. Severe winds --
potentially destructive with gusts upwards of 80 mph -- will become
increasingly likely as convection evolves into the evening hours.
..Cohen/Weiss.. 06/17/2017
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...SGF...EAX...TOP...ICT...DDC...
LAT...LON 37109867 37279953 37659969 38009953 38429896 39199744
39939509 40309396 40349325 39779312 38909344 38039459
37409662 37109867
from SPC Mesoscale Discussions http://bit.ly/2teGovX
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