U.S. Severe Weather Forecast (Convective Outlook)

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acus02 kwns 120549 
swody2 
Storm Prediction Center ac 120548 


Day 2 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1148 PM CST Tue Dec 11 2018 


Valid 131200z - 141200z 


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


... 
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. 


... 
Models continue to indicate further amplification within split 
westerlies emanating from the mid-latitude Pacific through this 
period. Troughing and ridging within these belts across the eastern 
Pacific into western North America may become increasingly in phase. 
However, the vigorous southern portion of a splitting tough across 
and east of The Rockies is forecast to continue digging sharply into 
the Southern Plains, where a significant embedded lower/mid 
tropospheric cyclone may evolve, while it gradually turns eastward 
toward the lower Mississippi Valley. 


Models generally indicate that this will be accompanied by a 
modestly deep and occluding surface low migrating eastward near or 
just south of the Southern Plains Red River. Secondary surface wave 
development still appears possible near/east of the southeast 
Louisiana Gulf Coast by late Thursday evening. 


Large-scale forcing for ascent associated with this evolving regime 
is expected to support considerable precipitation and embedded 
thunderstorm activity across the southeastern plains and Upper Texas 
coastal areas, into the western Gulf of Mexico, through much of the 
lower Mississippi Valley and remainder of the Gulf of Mexico. This 
probably will include at least some risk for severe thunderstorms. 
However, with the Gulf boundary layer only beginning to modify in 
the wake of recent cooling/drying, it still appears that severe 
weather potential, in general, will be mitigated over inland areas 
by weak warm sector boundary layer destabilization. 


..Ark-la-tex/lower Mississippi Valley/Gulf Coast... 
Broad brush 5 percent severe probabilities have been maintained 
across the region with some adjustment based on current expectations 
of the evolving warm sector. However, any developing severe weather 
potential during this period may ultimately become focused in a 
couple of distinct areas. 


Cloud cover/precipitation accompanying an initial band or cluster of 
convection (largely aided by forcing associated with an initial 
perturbation within the subtropical westerlies) probably will 
inhibit destabilization through much of the inland developing warm 
sector, as it spreads into and east of the lower Mississippi Valley. 
However, in the wake of this activity, a developing dry slot may 
allow for sufficient insolation to contribute to mixed layer cape on 
the order of 500 j/kg, beneath cold mid-level air near the Sabine 
valley into The Ark-la-tex by late Thursday afternoon. 


It appears possible that the exit region of a 90-100 kt 500 mb jet 
may overspread this instability axis before the onset of diurnal 
cooling, supporting discrete storm development across The Ark-la-tex 
vicinity, and perhaps southward through western/central Louisiana. 
Given the strong deep layer shear, this may include a couple of 
supercells. It remains unclear whether low-level hodographs will 
become large enough to support an appreciable risk for tornadoes, 
but activity will probably be accompanied by at least some risk for 
severe hail and wind before diminishing across the lower Mississippi 
Valley Thursday evening. 


Otherwise, the secondary surface frontal wave may provide another 
focus for isolated severe storm development by Tuesday night, across 
coastal areas between southeast Louisiana into the western Florida 
Panhandle. In the presence of strengthening deep layer wind fields 
and shear, somewhat better boundary layer moistening over the Gulf 
of Mexico may contribute to increasing instability across this area. 


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


.Kerr.. 12/12/2018 


$$