STORM2K

Mesoscale Discussion 0702
NWS Storm Prediction Center Norman OK
0121 PM CDT Mon May 20 2019

Areas affected...southwest and central OK

Concerning...Severe potential...Watch needed soon

Valid 201821Z - 201845Z

Probability of Watch Issuance...95 percent

SUMMARY...Environmental signals are continuing to point towards a
tornado outbreak with multiple strong to potentially violent
tornadoes across portions of western and central OK later this
afternoon into the evening.

DISCUSSION...Visible imagery shows a bubbling and destabilizing
boundary layer with upwards of 4000-4500 J/kg MLCAPE developing
across the warm sector over western and central OK. Surface
dewpoints are rising through the lower 70s degrees F across western
and central OK.

The 18z Fort Worth, TX upper air balloon showed a capping inversion
located just below 700mb. Recent runs of the RAP model show this
inversion less pronounced farther north. Despite temperatures
warming into the lower 80s over north TX into southwest OK, this
capping inversion has delayed convective initiation. This is
concerning for 2 reasons: 1) the wind profile continues to
strengthen across southwest and central OK with the Norman, OK upper
air balloon sampling 50kt flow around 850mb which is about 1-2 hours
earlier than forecast soundings were showing. 2) It does not appear
many storms will develop across southwest OK and resulting in
destructive storm-to-storm interference. In other words, tornadic
potential appears very high. Storms will likely initiate on the
north-end of the cloud streets over southwestern OK in the hotter
air and intensify and move northeast towards the I-40 and I-35
corridors later.

As such, the very rare combination of shear/buoyancy with many hours
of run-to-run consistency of the HRRR model showing discrete
supercells all point to a tornado outbreak developing later this
afternoon featuring strong to violent long-track tornadoes.

..Smith/Hart.. 05/20/2019

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0302 PM CDT Mon May 20 2019

Valid 202000Z - 211200Z

...THERE IS A HIGH RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
OKLAHOMA AND INTO PARTS OF WESTERN NORTH TEXAS AND THE TEXAS
PANHANDLE...

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS A LARGE
PORTION OF THE SOUTHERN PLAINS VICINITY...

...SUMMARY...
An outbreak of tornadoes, some potentially long-track and violent,
remains likely today into this evening over portions of northwest
Texas into western and central Oklahoma. More isolated but still
potentially dangerous severe weather, including tornadoes and
destructive winds and hail, remains possible in surrounding parts of
Texas, Oklahoma, Kansas, and Arkansas.

...Discussion...
Current expectations and reasoning laid out in prior outlooks
remains valid, with a potentially dangerous severe weather/tornado
outbreak in its initial stages at this time. Very few changes have
been made to the outlook areas, with only minor tweaks to shift the
northern fringe of the tornado risk a bit southward, due to current
and anticipated outflow boundary location. Otherwise, the initial
supercell storms have developed from the Texas South Plains region
northeast into western Oklahoma, with a rapid increase in risk
expected over the next couple of hours, and then lasting through the
evening and into the overnight period.

..Goss.. 05/20/2019

.PREV DISCUSSION... /ISSUED 1126 AM CDT Mon May 20 2019/

...Southern Plains...
A tornado outbreak is forecast to unfold this afternoon and evening
across parts of northwest TX and western/central OK. Moisture
continues to stream northward across the region, with dewpoints in
the 70s yielding very high afternoon MLCAPE values of 3000-5000
J/kg. Meanwhile, shear profiles are also rapidly increasing as a
50-60 knot southerly low-level jet strenghens across the area. This
is leading to a rare combination of extreme instability and large
hodographs as depicted on forecast soundings throughout the region.

Given the weak capping inversion, strong low-level theta-e
advection, and approaching large-scale forcing, all signs point to
the development of numerous intense supercells this afternoon across
the MDT and HIGH risk areas. Any storm that persists in this
environment will pose a risk of strong tornadoes, very large hail,
and damaging winds. The corridor of greatest concern, including a
threat of long-track and potentially violent tornadoes, will extend
from the southeast TX Panhandle into western and central Oklahoma.

Multiple rounds of severe storms are expected to affect these areas,
with new storms forming this evening over west TX and spreading
across north TX and much of OK overnight. These storms will
maintain a risk of large hail, damaging winds, and isolated
tornadoes through the night in some areas.

...Northeast States...
Relatively strong heating is occurring over New England and eastern
NY, where a moist and moderately unstable air mass is present.
Scattered afternoon thunderstorms are expected to form in this area,
and spread eastward toward the New England coast during the late
afternoon. Steepening low level lapse rates and westerly flow aloft
will promote a risk of gusty/damaging winds and some hail in the
stronger cells.