- Day Three
acus02 kwns 190540
Storm Prediction Center ac 190539
Day 2 convective outlook
National Weather Service Storm Prediction Center Norman OK
1139 PM CST Mon Feb 18 2019
Valid 201200z - 211200z
..there is a marginal risk of severe thunderstorms into the day
Wednesday across parts of southeastern Louisiana and Mississippi
into adjacent portion of southwestern Alabama...
Strong thunderstorms may continue to impact parts of the lower
Mississippi Valley into the day Wednesday, accompanied by at least
some risk for severe weather.
Latest model output suggests little appreciable change from prior
runs. The westerlies emanating from the mid-latitude Pacific appear
likely to remain amplified, with at least some further amplification
of embedded ridging over the northeast Pacific into downstream
troughing inland of the U.S. Pacific coast. The cyclonic regime is
likely to be reinforced by a strong short wave trough digging along
the coast, as a vigorous downstream impulse emerges from the
larger-scale western U.S. Troughing.
As the northwestern periphery of a prominent subtropical ridge,
centered east of the Bahamas, remains strong across parts of the
southeast, the lead impulse is forecast to accelerate around it,
into a broadly confluent regime near/north of the Great Lakes
region. Although it may undergo considerable deformation, models
suggest that it may still support the evolution of a modest cyclone
within deepening surface troughing across the upper Midwest and
Great Lakes region, as a gradual erosion of cold surface ridging
proceeds to the east of the Mississippi Valley.
Above the residual cold/stable surface-based air, weak
destabilization associated with a moist southerly return flow off
the western Gulf of Mexico may be contributing to considerable
convective development, including embedded thunderstorms, at the
outset of the period across the lower Mississippi and Ohio valleys.
Across the Ohio Valley, this likely will be aided by warm advection
associated with a strong low-level jet (including 50-70 kt at 850
mb). This jet is forecast weaken while shifting east-northeastward
across the central Appalachians and mid Atlantic region, but models
indicate forcing for ascent will support secondary frontal wave
development near/east of the northern mid Atlantic coast late
By 12z Thursday, the primary low-level frontal zone is expected to
become quasi-stationary to the west-southwest of this feature,
across the mid Atlantic coast and southern Appalachians through the
lower Mississippi Valley and Texas Gulf Coast region. This boundary
is expected to provide a continuing focus for mostly weak
thunderstorm development, associated with moist return flow above/to
the cool side of it.
..southeast Louisiana/Mississippi/adjacent Alabama...
Weak surface troughing is expected to provide the focus for boundary
layer moisture return (including surface dew points rising through
the lower/mid 60s f) and associated weak to modest destabilization
Tuesday night. It appears that this will linger in a corridor
inland of the coast through the day Wednesday, gradually shifting
across/east of the lower Mississippi Valley, but with little
enlargement, with a residual near-surface stable layer expected to
linger northward/northeastward into the Tennessee Valley and
Piedmont to the Lee of the southern Appalachians.
Before the strong low-level jet to the north progresses further away
from the region, it appears that lingering 30-40 kt southerly 850 mb
flow may contribute to sizable low-level hodographs and the
maintenance of an environment at least marginally conducive to
organized severe thunderstorm development, including supercells,
into the day Wednesday. This may include a risk for a tornado or
two, in addition to a few potentially damaging wind gusts.
..Pacific coast/intermountain west...
Despite the strength of the digging upper trough, a generally cold
low-level environment inland of coastal areas appears likely to
minimize the potential for thunderstorm activity.
..maximum risk by hazard...
Tornado: 2% - marginal
wind: 5% - marginal
hail: 5% - marginal