U.S. Severe Weather Forecast (Convective Outlook)

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Day Three

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acus03 kwns 210831 
swody3 
Storm Prediction Center ac 210830 


Day 3 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0230 am CST sun Dec 21 2014 


Valid 231200z - 241200z 


..there is a slight risk of severe thunderstorms from the lower MS valley into 
the Gulf coastal region... 


..there is a marginal risk of severe thunderstorms over the lower MS valley into a 
portion of the southeastern states and northern Florida... 


... 
Potential will exist for a few strong to severe thunderstorms from 
southern portions of the lower Mississippi Valley through the Gulf 
coastal region Tuesday into Tuesday night. The primary threats will 
be isolated damaging wind gusts and a couple of tornadoes. Some hail 
will also be possible...mainly over the lower Mississippi Valley 
region. 


... 


High-amplitude upper trough will advance slowly through the plains 
with an embedded southern stream shortwave trough reaching the lower MS 
valley region Tuesday night. Primary surface cyclone attendant to the 
northern-stream shortwave trough will weaken as it moves toward the western 
Great Lakes. The trailing cold front will continue through the MS 
valley and likely extend from the Great Lakes southward into Alabama by the end 
of this period. Weak cyclogenesis will also be possible in 
association with the southern-stream impulse...and this feature should 
lift northeastward along the front through MS into the Tennessee Valley overnight. A 
warm front should stall over the Gulf Coast region. 


..lower MS valley through the Gulf coastal region and northern Florida... 


Primary complicating factor this forecast is potential for numerous 
showers and thunderstorms to develop early in period over a portion 
of the southeastern states within zone of isentropic ascent along and north 
of coastal front. This should limit boundary-layer destabilization 
potential with northward extent away from the Gulf Coast. Greatest cape 
early Tuesday is likely over la and southern MS where remnant eml will 
have advected above western fringe of the moist axis. MUCAPE in this 
region may approach 1500 j/kg. Storms will likely increase during 
the day along and north of the warm front from the Gulf Coast area 
northward into the southeastern states promoted by a broad southerly low level jet. Given 
effective shear from 40-50 knots...potential will exist for a few 
supercells...and storms may become rooted near the surface over southern 
portions of the lower MS valley and Gulf Coast region. Other storms 
may develop as southeastward advancing front intercepts the moist axis. 
Activity will develop eastward during the day and overnight through the 
southeastern states and Gulf of Mexico and eventually into northern Florida. Will 
maintain a lower-end slight risk this update given the conditional 
nature of the threat. 


.Dial.. 12/21/2014