...THERE IS A HIGH RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF WEST
AND NORTHWEST TEXAS...THE EASTERN TEXAS PANHANDLE AND WESTERN
OKLAHOMA...
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
SOUTHEAST NEW YORK AND NEW ENGLAND...
...SUMMARY...
An outbreak of strong tornadoes and severe thunderstorms is expected
today across parts of the southern and central Plains. In addition,
many of the storms will have very large hail and wind damage. The
severe threat will be concentrated from west Texas and the Texas
Panhandle eastward across Oklahoma, Kansas into western Missouri and
western Arkansas. Additional severe storms with wind damage and hail
will be possible this afternoon from southeast New York into
southern and central New England.
...Tornado Outbreak Expected Across the Southern Plains Today Into
Tonight...
...Southern and Central Plains...
An impressive and potent upper-level trough will move quickly
eastward across the Desert Southwest today as a powerful 75 to 90
knot mid-level jet rounds the base of the trough. Ahead of the
system, a corridor of strong instability is forecast across the
Southern Plains from west Texas into the eastern Texas Panhandle and
eastward into western and central Oklahoma. This combined with steep
mid-level lapse rates and strong low-level shear will be very
favorable for severe storms. As the mid-level jet ejects
northeastward across the southern High Plains this afternoon and
evening, a tornado outbreak is likely across the southern Plains.
The tornado outbreak is expected to continue into the overnight
period. This event should result in a significant threat to life and
property.
RAP forecast soundings late this afternoon along the instability
corridor from Childress, Texas northeastward to Clinton, Oklahoma
show MLCAPE values of 3000 to 4500 J/kg with 0-6 km shear in the 50
to 65 kt range. In addition, hodographs are large and looped with
0-1 km shear values in the 30 to 40 kt range. This environment
should be very favorable for supercells and tornadoes. 0-3 km
storm-relative helicities are forecast to steadily increase from
about 300 m2/s2 in the late afternoon to about 450 m2/s2 by early
evening as an anomalously strong low-level jet becomes better
focused. This will be ideal for a tornado outbreak with strong
tornadoes upstream and to the west of the low-level jet.
The current thinking concerning the details is that the first round
of severe storms will begin early as thunderstorms initiate in west
Texas and move northeastward into the eastern Texas Panhandle by mid
to late morning. Initially, large hail will be the main threat but
as these storms mature, tornadoes will be possible with the stronger
and more dominant cells. Additional supercells with tornado
potential are expected to initiate near the warm front in western
and central Oklahoma. A tornado threat will transition to large hail
and wind damage as the storms move into Kansas to the north side of
the boundary. This first round of severe storms is forecast to move
northeastward, away from the warm sector, allowing for the
development of extreme instability during the mid to late afternoon
from northwest Texas into southwest Oklahoma.
The second round of severe storms is expected to start during the
late afternoon as repeat initiation takes place in west Texas. Rapid
supercell formation is forecast along the I-27 corridor from the
vicinity of Lubbock northward to just south of Amarillo. A cluster
of tornadic supercells is then forecast to move northeastward into
northwest Texas and the southeastern Texas Panhandle during the
early evening. Additional tornadic supercells are forecast to
rapidly develop in southwest Oklahoma and move northeastward into
west-central Oklahoma. At that time, the strengthening low-level jet
will couple with a highly progressive and seasonably strong
mid-level jet, making conditions favorable for long-track strong
tornadoes and possibly violent tornadoes.
The greatest threat for long-track tornadoes will exist along the
corridor from near Lubbock northeastward to Childress, Altus,
Lawton, Clinton to just west of the Oklahoma City and Enid
vicinities. After considerable deliberation, a High risk will be
issued for parts of west Texas, the southeastern Texas Panhandle
into western Oklahoma.
In addition to the tornado threat, conditions will be very favorable
for large hail and wind damage. Strong instability, enhanced
deep-layer shear and steep mid-level lapse rates will make
hailstones of greater than 2 inches in diameter possible with the
more intense supercells, mainly in west Texas and the western half
of Oklahoma. A wind-damage threat will also exist across much of the
southern Plains due to the expected intense nature of the storms.
The wind-damage threat, including some gusts above 70 kt, should
become widespread during the late evening into the overnight period
as squall line organizes and moves quickly eastward across the
southern Plains.
...Southeast New York/New England...
An upper-level trough will move across southern Quebec and the
Northeast today. At the surface, a cold front will advance eastward
across New York and into western New England. Ahead of the front,
surface dewpoints in the mid 60s F should result in destabilization
of the airmass by afternoon from southeast New York into much of
southern and central New England. Scattered thunderstorm development
is expected around midday along the cold front with this convection
moving eastward across the moist sector during the afternoon.
Forecast soundings along the instability axis from Springfield,
Massachusetts northeastward into Vermont at 21Z show MLCAPE values
peaking in the 1000 to 1500 J/kg range and have steep low-level
lapse rates. This combined with 0-6 km shear values around 35 kt
should be sufficient for multicells with wind damage potential. A
few rotating storms with a large-hail threat may also develop.
..Broyles/Wendt.. 05/20/2019
