Valid 221630Z – 231200Z
…THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE
SOUTHERN PLAINS TO THE MID-ATLANTIC STATES AND THE NORTHERN/CENTRAL
HIGH PLAINS…
…SUMMARY…
Isolated damaging winds are possible this afternoon and evening from
the southern Plains and Mid-South to the Mid-Atlantic States.
Isolated severe hail and wind are also possible over the northern
and central High Plains.
…Mid-Atlantic States/Carolinas…
A belt of cyclonically curved/moderately strong westerlies aloft
will persist over the Upper Ohio Valley and Mid-Atlantic region,
with a cold front gradually progressing southeastward across these
regions through tonight. Thunderstorms are expected to
develop/increase over the mountains and/or in association with
ongoing persistent clusters. As low-level lapse rates steepen,
damaging winds will be the primary risk. A few
sustained/semi-organized clusters of storms may materialize this
afternoon, particularly from south-central Pennsylvania southward to
near/east of the Blue Ridge in Virginia/Northern Carolina. However,
current thinking is that the overall severe storm coverage/risk
magnitude will be a bit lower as compared to prior days across the
region.
…Southeast Wyoming/Central High Plains…
To the north of an eastern Colorado-centered surface low, low-level
upslope flow and differential heating in vicinity of the higher
terrain is likely to contribute to isolated thunderstorm development
this afternoon. Storms should intensify as they move
east-southeastward within a moist/increasingly unstable environment.
A few instances of isolated severe hail will initially be possible.
Storms may gradually cluster with localized severe-caliber wind gust
potential this evening across the southern Nebraska
Panhandle/northeast Colorado vicinity, and possibly southwest
Nebraska/northwest Kansas.
…Southern/eastern Montana to northern High Plains…
Isolated to scattered thunderstorms are expected to develop across
this area during the afternoon, and into evening with eastward
extent. Isolated severe gusts/hail are the main concerns. A relative
concentration of convection is possible during about
00Z-06Z across portions of eastern Montana and perhaps northeastern
Wyoming. During that time frame, some of the stronger low-level mass
response and convergence (related to the approaching shortwave
trough), and perhaps the leading fringe of mid/upper synoptic
forcing, will impinge upon a narrow plume of relatively maximized
buoyancy and boundary-layer moisture. Pre-convective MLCAPE of
1000-2000 J/kg is possible this evening near an axis from RAP-GGW,
amidst well-mixed subcloud layers supporting strong-severe gust
potential. However, weak mid/upper-level winds suggest that severe
potential should remain fairly disorganized and/or short-lived.
…Southern Plains to Mid-South/Tennessee Valley…
Within a moist/unstable environment, surface-based thunderstorm
development later this afternoon will be focused along zones of
residual outflow/differential heating. While weak westerlies will
generally prevail, ample heating/buoyancy could support localized
severe-caliber downdrafts late this afternoon/early evening.
..Guyer/Bunting.. 08/22/2019
$$