ACUS01 KWNS 211958
SPC AC 211957
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0257 PM CDT Wed Aug 21 2019
Valid 212000Z - 221200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
THE NORTHEAST AND MID ATLANTIC REGION...AS WELL AS OVER PARTS OF THE
COLORADO FRONT RANGE...
Severe thunderstorms will continue this afternoon and evening across
parts of the Northeast/Mid-Atlantic States, while a few severe
storms will be possible across the central high Plains.
The overall outlook remains on track, with respect to prior forecast
reasoning. The main changes in this update will be to extend the
eastern U.S. SLGT risk a bit farther south across parts of the mid
Atlantic region, while removing northern portions of the risk in
parts of New England, and to include a small SLGT risk over the
Colorado Front Range.
In the East, clouds remain dense, and the airmass stable, over
northern portions of Vermont and New Hampshire, with the primary
severe risk likely to remain south of these areas. Meanwhile, with
recently issued WW #610 extending southward to the Chesapeake Bay
region, SLGT risk is correspondingly being expanded slightly
In Colorado, shear remains modest -- particularly with southward
extent. However, with moderate destabilization occurring, and thus
risk for locally intense cells within a narrow corridor, potential
for hail/wind with a few of the strongest storms warrants upgrade to
a small SLGT risk in this area.
Otherwise, no major changes to the outlook are required at this
.PREV DISCUSSION... /ISSUED 1132 AM CDT Wed Aug 21 2019/
A shortwave trough will continue to progress east-northeastward from
eastern New York toward northern New England, while a warm front
slowly spreads northward across southern New England. With broken
cloud cover lingering in most areas, modest overall destabilization
is expected along/south of the warm front where low-level/deep-layer
shear will be maximized. The environment will support the
possibility of supercells/bowing segments particularly across
southeast New York and southern New England, with severe hail/wind
possible along with some tornado risk. Multicells with damaging
winds are possible farther south within the warm sector. For
additional short-term details, see Mesoscale Discussion 1825.
...Kansas/Missouri/far southeast Nebraska to Missouri/Illinois...
The remnants of overnight convection continue to decay across the
region with cloud cover/outflow influencing an effective boundary
across southern portions of Kansas/Missouri. Surface-based
thunderstorms should develop/intensify later this afternoon
particularly across southern/eastern Kansas into western Missouri
within a moist/unstable environment. Relatively weak tropospheric
winds may limit overall storm organization, but the strongest storms
will pose a damaging wind/severe hail risk.
...Wyoming/Colorado Front Range to central High Plains...
Isolated to widely scattered thunderstorms should develop this
afternoon over the eastern mountains and foothills from northern
Wyoming across central/southern Colorado, offering the potential for
isolated severe hail and gusts. Activity is expected predominantly
in the post-frontal/upslope region where lift is maximized by a
combination of upslope flow and diabatic surface heating of the
higher terrain (minimizing MLCINH). Mid-level flow is forecast to be
modest; however, vertical shear will be stronger than over lower
elevations ahead of the front because of the backed boundary-layer
winds and relatively extended low-level hodographs. As such, a
mixture of supercellular and multicellular structures are possible.