495
ACUS11 KWNS 200057
SWOMCD
SPC MCD 200056
NEZ000-SDZ000-KSZ000-200200-

Mesoscale Discussion 1534
NWS Storm Prediction Center Norman OK
0756 PM CDT Sat Aug 19 2017

Areas affected...Portions of NE and northern KS

Concerning...Severe Thunderstorm Watch 458...

Valid 200056Z - 200200Z

The severe weather threat for Severe Thunderstorm Watch 458
continues.

SUMMARY...A cluster of storms across north-central NE will continue
to pose an isolated large hail and damaging wind threat, while other
storms have struggled to intensify across western portions of WW
458.

DISCUSSION...Recent water vapor satellite imagery depicts a
low-amplitude shortwave trough with embedded vorticity maximum
moving eastward over NE this evening. At the surface, a lee
trough/dryline extends southward from a weak surface low over
central SD across western NE into eastern CO. Multiple attempts at
convective initiation have occurred along the axis of the lee trough
across western NE and northwestern KS over the past several hours,
with none of them being successful in sustaining organized
thunderstorms. The airmass across much of NE and northern KS remains
very unstable as of 0050Z, with the 00Z sounding from North Platte
NE indicating MLCAPE around 2800 J/kg. Low and mid-level flow
remains generally modest, but does veer with height, and this
veering is the primary contributor to about 25-35 kt of effective
bulk shear.

A south-southwesterly low-level jet is expected to undergo some
strengthening this evening to around 30-35 kt, which may allow for
the small cluster of ongoing convection in north-central NE (with
dominant supercell in Loup County NE) to persist. Isolated large to
very large hail and damaging winds will be the main threat with this
activity as it moves generally east-southeastward. Current low-level
radar velocity trends also suggest a very near-term threat for a
tornado, as effective SRH becomes maximized with the modestly
strengthening low-level jet. With time, increasing convective
inhibition should lessen the possibility for a tornado. If current
radar trends continue, western portions of WW 458 could be canceled
early.

..Gleason.. 08/20/2017

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...FSD...OAX...ICT...GID...LBF...DDC...GLD...

LAT...LON   41380196 42800020 42789748 40039740 40049800 39259800
            38709908 38260116 38270194 41380196