U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus02 kwns 121721 
Storm Prediction Center ac 121720 

Day 2 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1120 am CST Wed Dec 12 2018 

Valid 131200z - 141200z 

..there is a marginal risk of severe thunderstorms across parts of 
the Arkansas-la-tex region into the lower Mississippi Valley and central 
Gulf Coast... 

Strong thunderstorms may impact parts of The Ark-la-tex region into 
the lower Mississippi Valley and north central Gulf Coast vicinity 
Thursday into Thursday night, accompanied by at least some risk for 
severe weather. 

Pair of shortwave troughs currently observable in water vapor 
imagery over the western Continental U.S. Will influence the sensible weather 
from the Southern Plains through the southeast on Thursday. The 
southernmost shortwave will continue to move across northern Mexico 
and will likely be centered over the far western Gulf of Mexico at 
the beginning of the day 2 period (i.E. 12z thursday). Northernmost 
shortwave, currently extending across Idaho and into northern NV, is 
expected to take a sharp dive southward across the central rockies, 
leading to a split for the northern stream and the development of a 
closed low over the southern High Plains by early in the day 2 

Strong height falls attendant to the second, significantly more 
amplified shortwave will spread across the Southern Plains, 
contributing to both increased forcing for ascent across the region 
as well as the development and deepening of a surface low expected 
to move across North Texas. A modestly moist and unstable air mass will 
likely be in place ahead of the system, from East Texas eastward 
through the lower MS valley, with some threat for a few strong to 
severe thunderstorms. 

..East Texas/lower MS valley/central Gulf Coast... 
Current surface observations reveal mid-50s dewpoints are currently 
south of a line arcing from iah (in southeast tx) westward to lrd 
(along the Texas/Mexico border in south tx). Dewpoints greater than 60 
are currently confided to the immediate southern Texas coast. This 
low-level moisture is expected to advect northward/northeastward 
within the persistent low/mid-level southerly/southeasterly flow 
anticipated throughout the day today. Consensus amongst the guidance 
is that mid 50s dewpoints will reach as far north as the arklatex 
region by 12z Thursday, with some further increase to the upper 
50s/low 60s possible by early Thursday afternoon. 

Interaction between the maturing cyclone and this low-level moisture 
(and resulting marginal instability) will result in the most 
coherent severe threat during the period. In this area (i.E. 
East/southeast Texas and western la), some modest air mass 
destabilization is possible between the mid-level dry slot and 
approaching surface low/occluded front. Strong vertical shear will 
likely compensate for the marginal thermodynamics and a few strong 
to severe storms are possible. Primary threat is hail but a brief 
tornado is also possible, particularly if any boundaries are left 
over from the early morning showers and thunderstorms and/or if 
southeasterly surface winds persist. 

A more spatially limited severe threat is possible farther southeast 
across southeast la and the immediate coastal areas of south MS, al, 
and the far western Florida Panhandle. A secondary surface low will 
likely develop during the late afternoon over southeast la near the 
triple point as the primary low occludes over northeast Texas. This 
second low is then expected to track eastward along the immediate 
central Gulf Coast into the western Florida Panhandle. This track will 
limit the inland penetration of the warm sector, tempering the areal 
extent of any potential severe threat. Given the strong vertical 
shear and proximity to the secondary surface low, a few storms may 
be capable of producing damaging wind gusts and perhaps even a brief 
tornado within about 75 miles of the coast. 

..maximum risk by hazard... 
Tornado: 2% - marginal 
wind: 5% - marginal 
hail: 5% - marginal 

.Mosier.. 12/12/2018