Convective Outlook

U.S. Severe Weather Forecast

acus01 kwns 131957 
Storm Prediction Center ac 131955 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0155 PM CST Thu Dec 13 2018 

Valid 132000z - 141200z 

..there is a marginal risk of severe thunderstorms across much of 
northeast Texas...and across parts of the Florida Panhandle... 

Isolated strong to severe thunderstorms may impact parts of The 
Ark-la-tex region through evening, and over parts of the central 
Gulf Coast/Florida Panhandle tonight. 

..northeast Texas region... 
Low pressure will continue to drift eastward across northeast Texas 
where cooling aloft and near-60 f dewpoints are contributing to 
sufficient instability for a few strong storms. Marginal hail 
appears to be the main threat, with perhaps a brief/weak tornado as 
lapse rates steepen. Overall, wind profiles are weak in the 
low-levels and do not favor any organized severe threat. 

..Florida Panhandle and vicinity... 
While most of the thunderstorm activity will be offshore tonight, a 
low-level jet increasing to 50 kt will eventually bring more 
unstable air toward the coastal Florida Panhandle. Given strong 
veering winds with height, will maintain low tornado probabilities, 
conditional on near-surface based instability late. 

.Jewell.. 12/13/2018 

Previous discussion... /issued 1005 am CST Thu Dec 13 2018/ 

Morning water vapor imagery shows a compact and progressive upper 
low digging southeastward into West Texas. The primary associated 
surface low is currently near Wichita Falls, and should remain in 
North Texas for most of the day. Low level winds in the warm sector 
are not particularly strong, but visible imagery suggests at least 
some breaks in the low clouds will aid in heating and vertical 
mixing of the boundary layer. This should steepen the low level 
lapse rates and help destabilize the warm sector to marginal values. 
12z cam solutions are not bullish on much coverage of storms, but 
most show at least a few cells this afternoon affecting the slight 
risk area. Forecast soundings suggest sufficient vertical shear for 
low-topped rotating cells capable of hail and gusty winds. Ambient 
vorticity in vicinity of the surface/upper low may also pose a risk 
of funnel clouds or a tornado or two. This threat should diminish 
rapidly after sunset. 

..central Gulf Coast region... 
Scattered thunderstorms are ongoing this morning off the coast of 
Texas/la, and should spread inland into parts of la/MS/al and the Florida 
Panhandle later today. The air mass offshore is only partially 
modified with dewpoints in the mid 60s, so significant 
destabilization northward is not expected. Nevertheless, strong 
wind fields beneath the southern stream jet may be sufficient for a 
few strong cells capable of gusty winds. 


Mesoscale Discussion

acus11 kwns 131916 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 131916 

Mesoscale discussion 1707 
National Weather Service Storm Prediction Center Norman OK 
0116 PM CST Thu Dec 13 2018 

Areas affected...north central and northeast Texas area 

Concerning...severe unlikely 

Valid 131916z - 132145z 

Probability of watch issuance...20 percent 

Summary...thunderstorms may pose a risk for mainly a few instances 
of marginally severe hail through early evening. A couple of locally 
strong wind gusts and perhaps a brief tornado are also possible. 
Overall threat does not appear sufficient for a ww issuance. 

Discussion...early this afternoon a cold front stretched from a weak 
surface low near Gainsville Texas southwest to near del Rio. A 
pre-frontal trough extends from near Dallas to near Huntsville, and 
the atmosphere has destabilized in a narrow corridor. However, 
extensive clouds and weak mid-level lapse rates have limited MLCAPE 
to 500-1000 j/kg across north central Texas and showers, and 
thunderstorms are currently developing along a pre-frontal trough. 
This activity may undergo modest intensification with additional 
storms possible along the cold front as forcing for ascent and 
steeper mid-level lapse rates attending a progressive shortwave 
trough begin to interact with western fringe of warm sector. The 
stronger winds aloft accompanying the upper trough will remain south 
of this region, with modest vertical shear (30-35 kt) supportive of 
multicells and possibly some marginal supercell structures. Hail 
approaching severe levels appears to be the main threat, but given 
cooling temperatures aloft, low LCLs and presence of the slow-moving 
pre-frontal boundary, a brief non-supercell tornado or two cannot be 
ruled out despite small 0-1 km hodographs. 

.Dial/Hart.. 12/13/2018 

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


Latitude...Lon 32329675 33039712 33919678 33999610 33289523 32289511 
31729544 31799626 32329675 

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