U.S. Severe Weather Forecast (Convective Outlook)

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 
are expected. 

.Edwards/Kerr.. 03/25/2019 


Mesoscale Discussion

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. 

.Kerr.. 03/25/2019 

..please see www.Spc.NOAA.Gov for graphic product... 


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