SPC AC 081959
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0159 PM CST Wed Feb 08 2023
Valid 082000Z - 091200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS THIS EVENING
ACROSS PORTIONS OF NORTHEAST LOUISIANA...SOUTHEAST ARKANSAS...AND
MUCH OF WESTERN AND CENTRAL MISSISSIPPI...
Severe thunderstorms are expected this afternoon into tonight,
mainly across parts of the lower into middle Mississippi Valley.
Some of these will be accompanied by a risk for tornadoes, a couple
of which could become strong this evening across parts of eastern
Louisiana and southeastern Arkansas into western and central
A significant uptick in convection has been observed in the last
hour along the cold front in eastern Texas, within the moisture
plume moving off the Gulf of Mexico, and within the uncapped
warm/moist airmass across Louisiana and southern Mississippi.
However, these storms are relatively unorganized thus far, owing to
the weak shear (~20-25 knots per area VWPs). However, as the trough
approaches and shear strengthens this evening, expect more storm
organization, including supercells capable of tornadoes. A few
tornadoes could be strong as the low-level jet strengthens to around
55 knots, elongating the low-level hodograph and doubling the 0-500m
shear (per RAP forecast soundings).
Farther north, the forecast remains on track. Low 60s dewpoints are
now into western Tennessee, which will advect northward rapidly this
evening and overnight as low-level flow strengthens.
.PREV DISCUSSION... /ISSUED 1027 AM CST Wed Feb 08 2023/
The more prominent belt of split mid-latitude westerlies is
undergoing considerable amplification across the eastern Pacific
into western North America. This will continue through this period,
with mid-level ridging building inland of the Canadian and U.S.
Pacific coast by late tonight. As this occurs, a vigorous
downstream short wave trough is forecast to dig sharply along the
Rockies, with mid-level flow ahead of it trending southwesterly and
strengthening across the southern Great Plains through the Ohio
A significant mid-level trough/elongating low is already beginning
to pivot east of the southern Rockies as it begins to interact with
a belt of westerlies emanating from the subtropical eastern Pacific.
The trough axis is likely to gradually take on an increasingly
negative tilt across Oklahoma and Texas during the day today, before
accelerating north-northeastward through the middle
Mississippi/lower Ohio Valley vicinity by 12Z Thursday. Models
continue to indicate that associated forcing for ascent will
contribute to significant surface cyclogenesis from near/northwest
of the Ark-La-Tex by late this afternoon into areas north-northeast
of the St. Louis area by the end of the period.
In the wake of a couple of significant recent cold intrusions,
boundary modification over the northwestern Gulf of Mexico is still
underway. Mid/upper 60s surface dew points have advected inland
within at least a shallow pre-cold frontal plume across Texas
coastal areas into portions of the Piney Woods. A somewhat more
substantive influx of Gulf moisture is forecast to overspread the
Louisiana coast through much of the lower Mississippi Valley later
today through tonight. Near the northwestern periphery of mid-level
subtropical ridging, centered and becoming a bit more prominent
across the Bahamas, mid/upper-levels are relatively warm, and lapse
rates might not become particularly steep. However, the development
of weak to moderate boundary-layer CAPE still appears probable
within the evolving warm sector, in the presence of strengthening
deep-layer shear which is expected to become sufficient for
organized convection, including supercells.
...Southeastern Great Plains into Mississippi Valley...
The primary mid-level trough may be preceded to its south and
southeast by one or two subtropical perturbations, and the influence
of associated forcing for ascent on thunderstorm development within
the plume of returning moisture, while the boundary-layer attempts
to destabilize inland of coastal areas, remains unclear.
At the present time, the low-level moisture return associated with
the stronger low-level flow (still around 40-50 kt around 850 mb) is
tending to be undercut by the eastward advancing cold front, to the
south of the developing surface low over northeast Texas.
Meanwhile, convection allowing models generally indicate that a
considerable amount of convection may commence in the destabilizing
warm sector, well ahead of the cold front, across portions of
Louisiana into Mississippi this afternoon. This would likely be
prior to substantive strengthening of the low-level wind fields and
associated hodographs, though the environment could be supportive of
at least weak updraft rotation.
Depending on the impact of earlier convective development, forcing
along and just ahead of the eastward advancing cold front likely
will become the focus for increasing vigorous thunderstorm
development late this afternoon and evening. This probably will
including one or two evolving lines, with supercells embedded within
and perhaps preceding it. Coupled with strengthening southerly 850
mb flow along a corridor near/east of the Mississippi River, as
surface cyclogenesis proceeds, a window of opportunity may develop
this evening for one or two sustained, long tracked supercells
capable of producing strong tornadoes.
The possible lingering influence of at least a shallow residual
stable surface-based layer results in more uncertainty concerning
severe weather potential closer to the track of the surface cyclone.
However, mid/upper forcing for ascent and deep-layer mean wind
fields/shear will be stronger across this region, and could
contribute to potential for damaging surface gusts and perhaps
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