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spc ac 200819

day 3 convective outlook
nws storm prediction center norman ok
0219 am cst wed feb 20 2019

valid 221200z - 231200z

...there is a marginal risk of severe thunderstorms friday afternoon
through friday night across parts of the lower mississippi valley
into the southern plains...

...summary...
strong thunderstorms may impact portions of the lower mississippi
valley friday afternoon, into portions of the southern plains by
late friday night, accompanied by at least some risk for severe
weather.

...discussion...
models continue to suggest that mid/upper flow will undergo at least
some transition across the eastern pacific during this period, as a
blocking ridge begins to become more prominent near the gulf of
alaska. downstream of this feature, another significant short wave
trough is forecast to continue digging toward the u.s. pacific
northwest. as this occurs, guidance indicates that a vigorous short
wave trough, initially near the southwestern u.s. international
border area at 12z friday, will remain progressive, and begin to
more rapidly pivot east-northeastward across new mexico and
southwest texas into the southern high plains by late friday night.
it appears that this will provide support for a rapidly developing
cyclone by the end of the period across the texas panhandle
vicinity.

meanwhile, mid/upper ridging within the mid-latitude and subtropical
westerlies is forecast to remain amplified across the mississippi
valley through the atlantic seaboard, to the north/northwest of
persistent prominent subtropical ridging (centered at mid-levels
east of the bahamas).

on the northwestern periphery of the subtropical ridge, weak
elevated destabilization above a warm frontal zone may be supporting
considerable thunderstorm development at the outset of the period in
a corridor from the ark-la-tex through the tennessee valley. this
boundary may remain a focus for continuing convection through much
of the period, while gradually shifting northward across the ozark
plateau and lower ohio valley.

additional thunderstorm development appears likely across parts of
the southern plains by late friday night, in response to increasing
large-scale ascent and destabilization associated with the impulse
emerging from the southwest.

...lower mississippi valley...
modest boundary-layer destabilization is forecast in a corridor
south of the initial warm frontal convection, across parts of
central louisiana into western mississippi by late friday afternoon.
this will be aided by daytime heating of a moistening air mass
characterized by lower/mid 60s+ f surface dew points. although it
is possible that this may occur beneath increasingly capping
mid-level warming, areas of enhanced low-level convergence may
support the initiation of scattered thunderstorms. if this occurs,
deep layer shear probably will be sufficiently strong to support
storms capable of producing at least marginally severe hail and
wind, which may linger into early evening.

...southern plains...
late friday night, increasing forcing for ascent and strengthening
wind fields within the moistening and destabilizing warm sector of
the developing cyclone may become supportive of increasing and
organizing convective development. by 12z saturday, forecast
soundings suggest thermodynamic profiles will become characterized
by increasing convective instability, and perhaps cape on the order
of 500-1000 j/kg. it is possible that this may still be mostly
based above a residual shallow stable near-surface layer, but storms
capable of producing severe hail and wind may not be out of the
question by daybreak.

..kerr.. 02/20/2019

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note: the next day 3 outlook is scheduled by 0830z