MD 0467 CONCERNING SEVERE POTENTIAL…WATCH POSSIBLE FOR PORTIONS OF CENTRAL/SOUTHERN/EASTERN KS…CENTRAL/WESTERN OK…WESTERN NORTH TX
Mesoscale Discussion 0467
NWS Storm Prediction Center Norman OK
0348 PM CDT Sun Apr 09 2017
Areas affected...Portions of central/southern/eastern
KS...central/western OK...western North TX
Concerning...Severe potential...Watch possible
Valid 092048Z - 092315Z
Probability of Watch Issuance...40 percent
SUMMARY...The area is being monitored for the possibility of
sporadic thunderstorm development this afternoon, with conditional
severe hail/wind potential spreading east-northeastward into the
evening. Watch issuance could be needed across portions of the
region, if sustained storm development were to become increasingly
possible.
DISCUSSION...Surface observations at 20Z indicate a dryline
extending from central KS near Salina, to northwest OK near Alva,
and then extending farther south into western North TX east of
Childress. East of the dryline, a steady influx of partially
modified Gulf moisture continues to extend northward, with surface
dewpoints around 60-63F. Breaks in mid/high-level cloud canopies,
attendant to a zone of DCVA preceding a midlevel shortwave trough,
are permitting diabatic surface-layer heating near and east of the
primary dryline circulation. The 18Z Lamont sounding reveals
substantial capping at the base of a prominent EML, though very
steep midlevel lapse rates (around 9.5 C/km in the 700-500-mb layer)
accompany this EML supporting 2000-3000 J/kg of MLCAPE.
There is considerable uncertainty regarding the exact details of
convective development -- if any -- along the dryline this
afternoon, as reflected by a wide variety of recent solutions from
convection-allowing models. Ultimately, the aforementioned capping
should greatly minimize convective coverage. However, modest ascent
preceding the aforementioned wave, coupled with diurnally steepened
low-level lapse rates, may adequately erode capping in proximity to
the dryline circulation for very isolated storm development --
perhaps in the 2130-2300Z time frame.
Observational data indicate a few potentially favored mesoscale
regimes for storm development:
(1) Western North Texas at the leading edge of a field of high-based
cumulus clouds intersecting a segment of the dryline that has been
locally sharpening and protruding eastward,
(2) Northwest OK into south-central KS near another dryline
protrusion/possible wave, and
(3) West-central OK where temperatures nearing 90F near/west of the
dryline are supporting deep dryline circulations along the southern
periphery of more substantial midlevel height falls.
If sustained deep convection were to evolve along the dryline,
supercell structures could ensue given 40-50 kt of effective shear
with a component orthogonal to the dryline. The aforementioned steep
midlevel lapse rates will be conditionally favorable for large hail
development -- perhaps significantly severe. Locally damaging wind
gusts may also conditionally occur. This activity would spread
east-northeastward into the evening hours, before somewhat greater
convective coverage potentially evolves across the lower Missouri
Valley vicinity this evening along a consolidating cold front.
..Cohen/Grams.. 04/09/2017
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...EAX...TSA...TOP...ICT...OUN...DDC...
LAT...LON 33979970 35359958 36849882 38009795 39379678 39439539
38739512 36799583 34909709 33799829 33559920 33979970
from SPC Mesoscale Discussions http://bit.ly/2pidyYK
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