Valid 302000Z – 311200Z
…THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
THE CENTRAL PLAINS…AND FROM SOUTHEAST MISSOURI EASTWARD INTO
Isolated severe thunderstorms are possible this afternoon and
evening across parts of the High Plains this afternoon, into central
Kansas overnight, and from southeast Missouri/southern Illinois into
…High Plains into central Kansas…
Capping remains over most of the area as of 20Z except over the
mountains. Ample heating will erode inhibition later today, with
isolated marginally severe storms capable of hail and gusty winds
from eastern WY into CO, supported by modest northwest flow aloft.
Overnight, additional storms in a separate regime are expected to
develop from southwest NE into central KS, where warm advection will
occur with strengthening southwest 850 mb winds. Lapse rates aloft
will remain relatively steep for this time of year, supporting
substantial elevated instability. Scattered storms are forecast by
many models, and may be capable of marginal hail. If a large enough
cluster of storms can form late in the period, severe wind gusts
will be possible as well despite the relatively cool boundary layer.
As such, have expanded 5% severe probabilities eastward into KS.
Storms propagating southward along a long-lived outflow boundary
continue to produce gusty winds, though nearly all below severe
limits. The presence of 2000 J/kg MLCAPE may support periodic
upticks in core intensity, but coverage appears to be decreasing
with time as winds aloft are weak. The 18Z FWD sounding also shows a
formidable midlevel subsidence inversion. As such, have opted to not
add any additional severe probabilities ahead of the outflow
…MO into OH…
A small area of unstable air ahead of an MCV may provide enhanced
shear for an isolated supercell, with either brief tornado, damaging
wind, or marginal hail threat. For more information see mesoscale
discussions 1900 and 1901.
.PREV DISCUSSION… /ISSUED 1129 AM CDT Fri Aug 30 2019/
Post-frontal upslope flow will be common from northeast New Mexico
to eastern Wyoming today, maintaining upper 40s to mid 50s surface
dewpoints at peak heating. This should support a plume of modest
MLCAPE of 500-1500 J/kg. Stronger/confluent mid-level westerlies
will generally be confined to the Wyoming portion of the region
where 500-mb flow of 35-45 kt is anticipated, with weaker winds
southward along the Front Range.
Isolated to scattered thunderstorms are expected to develop by mid
to late afternoon over the higher terrain. A few of these storms
should become supercellular for a couple hours across eastern
Wyoming to northeast Colorado. Abundant MLCIN with eastward extent
on the plains and lack of stronger forcing for ascent should keep
severe hail and wind coverage low.
…South-central/southeast Missouri to southern Ohio…
An MCV continues to move slowly eastward over west-central Missouri
late this morning. While this MCV may tend to weaken today, a belt
of modestly enhanced low/mid-level winds accompanying the MCV will
coincide with a front across south-central/southeast Missouri into
southern Illinois. There is a risk for a couple supercells capable
of a tornado and isolated damaging winds, particularly along and
south/southeast of I-44 in southeast Missouri, as well as southwest
Illinois. Farther to the east, a weakly convergent surface front
might aid in small multicell clusters capable of locally damaging
wind across southern Indiana/northern Kentucky to southern Ohio.
Composite outflow/effective front continues to progress
south/southwestward across the Texas Panhandle and Red River
vicinity. Surface-based late afternoon redevelopment will probably
be confined to the Texas Panhandle and possibly far western Oklahoma
near the intersection of the composite outflow/front and dryline. A
few severe thunderstorms are possible, but weakening deep-layer
shear across the region will serve to limit the overall risk.
On the immediate southern periphery of an upper ridge, isolated
thunderstorms are expected to develop over/near the mountains of
southeast Arizona and drift west-southwestward with aid of modestly
enhanced easterly mid-level winds. A reservoir of moist/unstable air
may allow for some relatively stout storms, with strong/gusty
outflow winds a possibility as they move across southeast Arizona.