- Day Three
acus01 kwns 251252
Storm Prediction Center ac 251251
Day 1 convective outlook
National Weather Service Storm Prediction Center Norman OK
0751 am CDT Mon Mar 25 2019
Valid 251300z - 261200z
..there is a slight risk of severe thunderstorms over portions of
Alabama and Georgia...
Severe thunderstorms are possible over portions of Alabama and
Georgia this afternoon and evening. Hail is the primary threat.
A very large, deep mid/upper-level cyclone near the northern tip of
Labrador will remain in that area through the period, rendering
broadly cyclonic flow across much of the central/eastern Continental U.S..
within the southern branch of that flow, two shortwave perturbations
will be most prominent:
1. A small cyclone now located over central IL, with troughing
southwestward across the arklatex region. This feature should
transition to an entirely open-wave trough moving east-southeastward
to the southern Appalachians vicinity by 00z, then the coastal
Carolinas and Georgia by 12z.
2. An upstream trough -- now evident in moisture channel imagery
over portions of Wyoming/Colorado -- and forecast to strengthen as it moves
over the Ozarks late in this period.
Meanwhile, a large synoptic cyclone will remain offshore from the
West Coast. However, a basal shortwave perturbation -- now located
about 450-500 nm west of sfo -- should pivot northeastward across
parts of northwestern California and western or this afternoon and evening,
contributing to low/middle-level destabilization and related general
thunder potential there.
At the surface, the 11z analysis showed a cold front from a weak low
over the lower Ohio Valley, across southeastern Arkansas and central Texas.
By 00z the front should reach middle/eastern TN, southwestern al,
central la, and the middle/Upper Texas coastal plain. By 12z, the low
will have shifted/redeveloped offshore from the northern NC Outer
Banks. The front then should extend across southeastern GA, the
eastern Florida Panhandle and the northern Gulf.
..southeastern Continental U.S....
scattered thunderstorms are expected to develop near the front today
across portions of Alabama and eastern MS, moving eastward to
southeastward across the outlook area. Isolated to widely scattered
thunderstorms also may form in the prefrontal warm sector. Large
hail will be the main threat, but isolated severe gusts and widely
scattered damaging convective winds also are possible. A
combination of moist/warm advection and diurnal heating will
destabilize the prefrontal boundary layer enough to support 500-1000
j/kg MLCAPE, locally higher. Despite relatively veered/westerly
prefrontal surface wind component, sufficient speed shear will exist
to yield 40-50 kt effective-shear magnitudes, with motion off the
hodograph to the east-southeast and southeast possible in any
Despite the weak mlcinh and resultant profusion of convection
expected, sufficiently orthogonal winds aloft are expected (with
respect to orientation of convective forcing along/ahead of the
front) to support discrete to semi-discrete modes for much of the
convective cycle. A broken to solid band of thunderstorms may
evolve over portions of eastern Alabama and Georgia this evening, offering
somewhat greater wind potential. However, this threat is
conditional enough on uncertain Mode details, both in terms of
timing and clustering, that probabilities of 15% or greater do not
yet appear warranted. Still, the outlook has been expanded
southeastward somewhat over Georgia and the Savannah River region. This
will give the potential band of convection more room to weaken below
severe levels this evening. If it organizes a cold pool, this
activity may be more of a solid line with bowing segments, forced by
leading-edge lift to persist somewhat deeper into stabilizing
boundary-layer air (with time and eastward extent) before weakening
enough to lose its damaging-wind and localized hail threat.
Though the greatest concentration of convection is forecast in and
near the slight/15% risk area, isolated severe may occur from near-
frontal thunderstorms this afternoon into early evening as far
southeast as the Upper Texas coastal plain as well. Although low-level
flow will be weak in this area, with small hodographs, 30-40-kt
effective-shear magnitudes with 1500-2000 j/kg MLCAPE may support
severe potential with any sustained storms in this regime. Coverage
is in question due to stronger mlcinh than farther poleward along
the front, although higher Theta-E and stronger diurnal heating also
acus11 kwns 250648
sels mesoscale discussion
Storm Prediction Center mesoscale discussion 250647
Mesoscale discussion 0238
National Weather Service Storm Prediction Center Norman OK
0147 am CDT Mon Mar 25 2019
Areas affected...parts of northeast Texas...northwest Louisiana and
adjacent southern Arkansas
Concerning...severe potential...watch unlikely
Valid 250647z - 250815z
Probability of watch issuance...5 percent
Summary...some risk for severe hail and wind may linger in stronger
storms for another hour or two, mainly across the Interstate 20
corridor of northeast Texas, before likely diminishing by 4-5 am
CDT. An additional severe weather watch is not anticipated.
Discussion...the most vigorous thunderstorm development is now
generally focused west-northwest through north/northeast of Tyler
TX, within a remnant axis of stronger, but waning boundary layer
destabilization associated with yesterday's daytime heating, and a
return flow of Gulf moisture that persists. This now appears to be
just ahead of a southward advancing surface cold front, which may
gradually tend to undercut the stronger convection and associated
unstable boundary layer air through 09-10z, as it progresses across
the Interstate 20 corridor. As this occurs, storm intensities are
expected to diminish. Until then, some risk for severe hail and
gusty surface winds may remain possible in isolated stronger storms
for another hour or two.
..please see www.Spc.NOAA.Gov for graphic product...
Latitude...Lon 32369573 32539485 32799390 33039328 32919297 32209356
31919510 32089642 32369573