Definitely a rarity;
SPC AC 180730
Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0230 AM CDT Sat May 18 2019
Valid 201200Z - 211200Z
...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS THE
EASTERN TX PANHANDLE...NORTHWEST TX...WESTERN/CENTRAL OK...AND FAR
SOUTH-CENTRAL KS...
...SUMMARY...
Severe thunderstorms capable of all severe hazards, including strong
tornadoes, are expected across portions of the southern Plains on
Monday.
...SIGNIFICANT SEVERE WEATHER EVENT POSSIBLE ACROSS THE SOUTHERN
PLAINS ON MONDAY...
...Synopsis...
Active upper pattern will continue on Monday as one shortwave trough
progresses through the Northeast while another ejects through the
base of the deep upper trough over the western CONUS late in the
period.
Subtropical ridging will remain in place over the Gulf of Mexico and
Southeast, resulting in the development of strong southwesterly flow
aloft ahead of the western CONUS shortwave. This strong flow will
remain in place throughout the day, likely increasing to near 100 kt
at 500 mb early Tuesday morning.
Surface pattern will feature a deepening lee cyclone over the
central High Plains with a dryline extending southward across the
eastern TX Panhandle and a warm front quickly moving northward
through OK.
...Southern Plains...
Guidance is in good agreement that the ingredients are in place for
a potentially significant severe weather event on Monday. A sharp
warm front is expected to move northward throughout the day,
starting from an early day position near the River Red and reaching
the OK/KS border by 00Z. Air mass south of this warm front will be
very moist (i.e. dewpoints in the upper 60s/low 70s) and unstable.
Consequently, moderate to strong instability will likely to develop
across the eastern TX Panhandle, northwest TX and much of OK, even
if strong diurnal heating does not occur. Current expectation is for
temperatures in this region to reach the low/mid 70s by late
morning/early afternoon with some areas farther east reaching
mid/upper 70s.
Kinematic environment is even more impressive than the thermodynamic
environment. 60-70 kt of southwesterly 500 mb flow will gradually
spread eastward/northward across the TX Panhandle and into OK and
KS. At same time, a strong and persistent low-level jet will be in
place, with 40+ kt at 850 mb throughout the period. Surface winds
within the warm sector will likely be southeasterly at 15 to 20 kt.
All of these factors result in wind profiles very favorable for
discrete supercells capable of all severe hazards, including
significant tornadoes.
Given that overall large-scale forcing for ascent is minimal
throughout much of the day, much of the afternoon and evening
activity is currently expected to initiate along the dryline and
within the warm sector, with a discrete storm mode favored. As the
shortwave ejects out later in the period, a more linear MCS may
develop, resulting in a second round of severe thunderstorms Monday
night into Tuesday morning.
...Northeast...
Thunderstorms are expected to develop along and ahead of a cold
front progressing across the region. Favorable low-level moisture
ahead of this front as well as strong unidirectional wind fields
will result in the potential for a few strong to severe storms.
Damaging wind gusts are the primary severe threat. Uncertainty
regarding coverage precludes higher severe probabilities with this
forecast.
..Mosier.. 05/18/2019
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