Day 1 Severe Weather Outlook

Valid 151300Z – 161200Z


Isolated severe thunderstorms are possible from parts of the Ozarks
to central Texas and across portions of the Gulf Coast States.

In mid/upper levels, a progressive, somewhat complex pattern will be
evident over most of the CONUS, east of a synoptic ridge forecast to
progress across the Great Basin and northern Rockies. A strong
shortwave trough — now apparent in moisture-channel imagery over
the Dakotas with an embedded low near DVL — will dig southeastward
and amplify further. By 12Z, a well-defined cyclone should be
centered over northern Lower MI, with trough southwestward across
the lower Ohio Valley and Mid-South region. A weaker, positively
tilted, southern-stream perturbation — initially located from
northern NM to southwestern AZ — will move east-southeastward. By
12Z, this feature should extend from northwest TX to northern
Chihuahua — with a weak 500-mb low possibly taking shape in the
INK/MAF area.

At the surface, the 11Z chart showed a low over southeastern MN,
with cold front across central IA, northwestern MO, south-central
KS, and northeastern NM. The low should move across WI today,
occluding and becoming nearly vertically stacked with the mid/upper
low by the end of the period. The cold front will sweep
southeastward across the southern Plains and lower Missouri/mid
Mississippi Valleys today. By 00Z the cold front should reach
southwestern IL, southeastern MO, southeastern OK, and north-central
through southwest TX. By 12Z, it should reach eastern OH, middle
TN, central MS, and the mid/upper TX coast. Meanwhile, the Gulf
warm front should move inland, decelerating but becoming better-
defined near the south rim of a persistent corridor of precip that
is reinforcing boundary-layer static stability across inland
sections of MS/AL/GA.

…Ozarks to central TX…
Widely scattered thunderstorms should develop as the cold front
impinges on a plume of favorable warm-sector/return-flow moisture
this afternoon and evening, from north-central/northeast TX across
eastern OK into the Ozarks, offering sporadic strong/locally severe
gusts and hail. A broken band of thunderstorms may extend well
northeastward into a narrow corridor of progressively weaker and
less surface-based buoyancy toward IL/IN/OH. The southwestern limit
of frontal convection should be its intersection with a dryline —
now located over the southeastern Panhandle and South Plains — that
should mix southeastward across northwest and parts of north-central
TX ahead of the front, before the front overtakes it this evening.

Rich low-level moisture will advect northeastward across the outlook
area ahead of the front, with surface dew points commonly in the mid
60s to low 70s F. This, along with relatively steep midlevel lapse
rates and areas of sporadic heating beneath high-cloud breaks,
should contribute to peak preconvective MLCAPE in the 2000-3000 J/kg
range from eastern OK into the Arklatex region. Weak near-surface
winds will limit low-level shear and hodograph size, though
sufficient flow aloft will exist to support 40-50-kt effective-shear
magnitudes. As such, supercells and organized multicells each are

Additional convection may form this afternoon in a regime of greater
moisture (1.75-2.25-inch PW, per regional RAOBs and GPS-based
readings) and weaker MLCINH — but also, more-modest deep shear and
veered low-level winds — across parts of central/east TX. Damaging
gusts will be the main threat with this activity as well, especially
if any upscale clustering and cold-pool aggregation occur.

Farther northeast toward the lower Ohio Valley, isolated strong/
damaging gusts cannot be ruled out, but the potential is very
conditional and uncertain at this stage, given the narrow/limited
and weak corridor of any surface-based instability. That corridor
will be monitored in subsequent outlook cycles for a more
unconditional wind threat developing, given the strength of winds
aloft and increase in large-scale forcing for ascent preceding the
amplifying northern-stream perturbation.

…Eastern LA to eastern Gulf Coast…
Scattered thunderstorms in episodic clusters are expected to develop
across the region and move eastward to east-southeastward in the
antecedent precip area and warm-frontal zone, and perhaps into part
of the warm sector. Associated severe potential still appears
isolated, marginal and rather poorly organized, mainly in the form
of damaging to near-severe gusts in the most water-loaded

Though diurnal heating will be limited by cloud cover, ample
boundary-layer theta-e will exist to support relatively uninhibited
MLCAPE of 500-1500 J/kg by mid-afternoon on and south of the
thickest cloud/precip plume. The wind profile will be characterized
by generally modest low-level flow. Small low-level hodographs are
expected, except along the warm front where SRH and vorticity are
locally enhanced, but still amidst weak speeds. However, deep shear
will be favorable for organized convection, with forecast effective-
shear magnitudes in the 35-45-kt range. Strong anvil-level/
ventilating flow aloft is expected, near the southern rim of a
strengthening west-southwesterly 250-mb jet. This eastern lobe of
the severe risk is rather tenuous and more fuzzy-edged in character
than implied by a sharp line on a map, owing to the expected messy
modes, modest lapse rates, mesoscale boundary uncertainties, and
subtlety of forcing away from the immediate warm front.

..Edwards/Goss.. 10/15/2019


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