Valid 021630Z – 031200Z
…THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS THIS
AFTERNOON/EVENING FROM NORTHERN OK TO NORTHERN MO…AND FROM
NORTHEAST PA TO PARTS OF SOUTHERN NEW ENGLAND…
…SUMMARY…
Isolated damaging gusts will be possible this afternoon/evening from
northern Oklahoma to northern Missouri, and from northeast
Pennsylvania to parts of southern New England.
…Northern OK to northern MO this afternoon/evening…
A midlevel shortwave trough over the central/northern Rockies will
eject east-northeastward to the upper MS Valley by the end of the
period, around the northwest periphery of the persistent ridge over
the Southeast. A weak surface wave is expected to develop
east-northeastward along a quasi-stationary surface front from
eastern KS later this afternoon to IL/IN overnight. The wave will
remain weak as the stronger large-scale forcing for ascent is
displaced largely to the cool side of the surface front. A broken
band of convection will likely accompany the weak wave along the
front from eastern KS into MO late this afternoon through late
evening.
Multiple days of convection across the southern High Plains have
reduced midlevel lapse rates near the front from the TX Panhandle/OK
to MO. Thus, buoyancy will be rather modest (MLCAPE 500-1500 J/kg),
driven primarily by surface heating and boundary-layer dewpoints
near 70 F. There will be a narrow zone of enhanced deep-layer shear
along the front this afternoon/evening, which could support a few
organized/marginal supercell storms capable of producing isolated
damaging gusts, and perhaps a brief tornado. Still, the rather
modest buoyancy/lapse rates and marginal low-level shear in the warm
sector suggest that only low wind and tornado probabilities are
warranted this afternoon/evening.
…Northeast PA to parts of southern New England this afternoon…
A series of subtle perturbations will move east-southeastward from
the lower Great Lakes to southern New England through this evening,
coincident with surface cold front that will continue moving
southward. Surface heating south of the front, where boundary-layer
dewpoints are in the mid-upper 60s, will contribute to some
destabilization and the potential for convection along the front
this afternoon. However, warm temperatures aloft and poor lapse
rates will limit the depth of buoyancy and updraft intensity.
Still, deep-layer west-northwesterly shear of 35-40 kt and steep
low-level lapse rates will support some potential for low-topped,
organized convection with strong outflow winds.
..Thompson/Kerr.. 10/02/2019
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