Valid 241200Z – 251200Z
…THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
THE CENTRAL AND SOUTHERN PLAINS THIS AFTERNOON THROUGH TONIGHT…
…SUMMARY…
Severe storms capable of widespread damaging winds, very large hail
and a couple of tornadoes are expected late this afternoon into
tonight across parts of the central and southern Plains. Additional
isolated severe storms capable of hail and strong gusts are possible
across parts of western North Dakota this afternoon and evening.
…Central/Southern Plains…
Decaying remnants of overnight convection will move across the
central/southern Plains vicinity during the morning. Cloud cover is
likely to inhibit convective redevelopment for much of the day, but
south/southeasterly low level flow will maintain mid 60s to low 70s
dewpoints across much of OK/KS westward toward a surface trough
across far eastern CO into the OK/TX Panhandles. Cloud cover will
remain across much of NE to the north of an effective warm front
just north of the NE/KS border. However, partial clearing west of
the I-35 corridor in OK/KS will aid in a corridor of strong
destabilization by late afternoon. While the main mid/upper level
trough will shift eastward across the northern Plains, guidance is
in good agreement that a strong shortwave impulse will migrate
through northwest flow aloft from eastern CO into western KS/OK.
Forecast soundings depict unusually strong vertical shear for this
time of year, with effective shear values from 35-50 kt.
Furthermore, strong, vertically veering winds through around 3 km
will result in large, curved low-level hodographs. Finally, during
the evening, a southerly low-level jet is forecast to increase to
around 40 kt across the southern Plains.
Most guidance, CAMs and otherwise, are remarkably consistent in
developing isolated cells by late afternoon/early evening in
convergent low level flow near a strengthening surface low over
eastern CO. Initial cells are expected in the vicinity of the CO/KS
border into southwest NE and perhaps southward along the surface
trough toward the OK/northern TX Panhandles. Any cells that remain
discrete during this initial development will pose a threat for very
large hail (possibly greater than 2 inches in diameter) given
midlevel lapse rates greater than 8 C/km and supercell wind
profiles. Additionally, aforementioned low level hodographs and deep
boundary-layer moisture will support potential for a couple of
tornadoes. As ascent increases with the approach of the midlevel
shortwave in conjunction with the increasing low-level jet, storms
are expected to grow upscale into one or more bowing segments
tracking east/southeast across KS/OK and perhaps the northeast TX
Panhandle. Given the overall thermodynamic environment and the
expectation that a strong cold pool will be generated given the
extent of forecast convection, widespread damaging winds appear
possible across portions of western and central KS/OK into parts of
the OK/TX Panhandles during the evening and nighttime hours.
…Western North Dakota…
The main upper-level shortwave trough will pivot eastward from the
northern Rockies to the northern Plains today. However, stronger
deep-layer flow will remain displaced to the west of the northern
Plains. Midlevel lapse rates also are forecast to be somewhat
modest, from around 6.5-7.5 C/km, despite stronger height falls and
cooling aloft after 00z. Nevertheless, southerly low-level flow will
maintain low to mid 60s dewpoints and 1000-2000 J/kg MLCAPE will
develop by late afternoon. Isolated cells are expected to develop as
ascent increases toward 00z. Effective shear around 25-35 kt will be
sufficient for a few organized storms capable of hail. Steep
low-level lapse rates and weak 0-3 km winds will also support a few
strong downbursts.
..Leitman/Wendt.. 08/24/2019
$$