OKC No Severe Threat, Eastern Oklahoma Under the Gun


As of the time of this post, the dryline is moving through Oklahoma City. West sides of town, it’s clear with increasing fire danger and winds. I will write a post on that shortly. Eastern Oklahoma, the moisture return is increasing rapidly, cape values, through the roof. This means one thing. Major severe weather outbreak. Severe hail, over 3 inches in diameter, straight line winds of 80+ mph & long-track supercells with violent, strong long-track tornadoes are possible in eastern Oklahoma, southeastern Kansas, portions of southwestern Missouri, western Arkansas & northeastern Texas are most likely to get these conditions. Below is what the Storm Prediction Center is saying about this life-threatening & potentially dangerous situation.

Day 1 convective outlook
National Weather Service Storm Prediction Center Norman OK
1111 am CDT Thursday Apr 14 2011

Valid 141630z – 151200z

..there is a MDT risk of severe thunderstorms from southeastern Kansas/southwestern MO southward through
eastern OK far western Arkansas into portions of northestern Texas…

..there is a slight risk of severe thunderstorms from portions of the central
and Southern Plains into parts of the lower MS valley…

..central and Southern Plains…

..Severe thunderstorm and tornado outbreak expected later this
afternoon and tonight…

Developing upper low over Colorado/nm will deepen east-northeastward into central Kansas by
tonight as powerful upstream jet and cold advection rotate southeastward
across southern rockies and out into the Southern Plains. Surface low northwestern OK
deepens north-northeastward into Kansas this afternoon while a secondary low takes
shape by this evening southern OK/Texas border in response to approach of
the upstream jet and large scale ascent.

Parameters favorable for the initiation of the forecast outbreak of
severe thunderstorms will focus on the dry line by middle/late
afternoon. From the surface low in Kansas the dry line should mix out
to a position from near rsl south-southeastward to about ict and then vicinity
I-35 into northern Texas.

The only question will be the moisture return but given the very
steep lapse rates and strong heating…strong instability will
develop with MLCAPES at or above 2500 j/kg northward ahead of dry line into
central/southeastern Kansas.

Discrete thunderstorm development will take place by middle/late
afternoon beneath strongly diffluent upper jet spreading across the
dryline. The strong instability combined with strong deep layer
vertical wind shear /near 70 knots in the 0-8 km layer/ will favor a
few longer-lived supercells. Very large hail will develop rather
quickly once initiation occurs. Low-level hodograph structure also
forecast to enlarge by later this afternoon and evening as low level
jet backs and increases…with effective srh values increasing to
200-400 m2 S-2. This supports the development of tornadic
supercells…with potential for strong tornados.

With the secondary low development near the Red River this
evening…high res models support a greater potential for long lived
tornadic supercells this evening across southeastern OK. Deeper moisture and
the diffluence of the approaching 120kt upper jet maximum will be
focusing on this area by this evening and it will be monitored for a
possible upgrade in the afternoon update if this scenario seems
likely to play out.

Surface cold front currently northwestern OK southwestward into Texas Panhandle is
forecast to rapidly move across eastern OK into western Arkansas after 00z.
Strengthening low-level linear forcing for ascent is expected to aid
in upscale growth to a qlcs structure. This activity will likely
move across Arkansas and southern MO overnight…posing a threat for damaging
winds. There will continue to be tornado potential with embedded
supercell structures.

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