U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 181657 
Storm Prediction Center ac 181656 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1156 am CDT sun Mar 18 2018 

Valid 181630z - 191200z 

..there is a slight risk of severe thunderstorms across the 
Southern Plains to the southeast states... 

..there is a marginal risk of severe thunderstorms across the 
central/Southern Plains to the southeast states... 

Thunderstorms with large hail and a tornado risk are possible 
especially across north and East Texas late this afternoon into 
evening, with additional severe thunderstorms possible across other 
parts of the south-Central Plains to southeast states. 

..North/East Texas and far southern Oklahoma to arklatex... 
The potential exists for locally intense storm development later 
this afternoon/early evening, but a number of questions remain 
regarding the likelihood and locations/coverage of deep convective 
development. Along these lines, various convection-allowing models 
have shown semi-dramatic sub-regional spatial shifts between 00z and 
12z of preferred severe corridors later today, while various hrrr 
runs have also exhibited considerable run-to-run variability 
(supercells vs. Essentially no development) this morning. 

Scattered showers and some thunderstorms along with multi-layer 
cloud cover remain prevalent across the region at midday, related to 
east/northeastward-transitioning southern-stream forcing for ascent 
embedded with a strong (100+ kt at 250 mb) subtropical jet stream. 
In the wake of this scattered precipitation/thicker clouds, cloud 
breaks and some additional low-level moist influx should allow for 
relatively rapid destabilization especially across 
north-central/east-central Texas to the near/east of a dryline and 
along/south of an east/southeastward-extending front. 

But given some hindered heating through early afternoon and the 
early timing of the aforementioned southern-stream impulse, the 
likelihood and extent of deep convective development later today 
remains questionable, particularly given that areas such as 
north-central Texas may be influenced by subsidence aloft during 
peak heating. Accordingly, the overall scenario seemingly remains 
largely conditional, with the notion that any sustained 
surface-rooted development could evolve into supercells capable of 
very large hail and some tornado risk in the presence of steep 
mid-level lapse rates, moderate buoyancy, and favorable hodographs 
for large diameter (potentially significant 2+ inch) hail. 

Further outlook refinements/adjustments can be expected with the 20z 

..lower Mississippi Valley to southeast states... 
A weak impulse or two (and/or mcv) should semi-focus thunderstorm 
clusters across the region today, such as is occurring across 
southern Mississippi at midday. While buoyancy will not be overly 
strong, 40+ kt effective shear could support some bowing segments 
and possibly even a transient supercell or two. Damaging winds and 
possibly some hail should be the primary concerns. 

..portions of Texas Panhandle/western Oklahoma into Kansas... 
At least some severe-weather potential should exist later this 
afternoon through early evening with anticipated low-topped storm 
development across the region. Very limited moisture will exist 
within/north of a narrowing warm sector, but steep lapse rates and 
moderately strong wind profiles could support some strong to severe 
storms across the Texas Panhandle/northwest Oklahoma northeastward 
into southern Kansas. 

.Guyer/marsh.. 03/18/2018 


Mesoscale Discussion

acus11 kwns 180135 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 180135 

Mesoscale discussion 0132 
National Weather Service Storm Prediction Center Norman OK 
0835 PM CDT Sat Mar 17 2018 

Areas affected...east central Texas 

Concerning...Severe Thunderstorm Watch 9... 

Valid 180135z - 180230z 

The severe weather threat for Severe Thunderstorm Watch 9 continues. 

Summary...isolated damaging wind and large hail remain possible over 
east central Texas through 04z, but overall trend should be for 
storms to weaken after 03z. 

Discussion...as of mid evening, storms persist over the eastern part 
of central Texas from east of kileen to west of Lufkin. The strongest 
storms are developing along an outflow boundary interacting with a 
modest southerly low-level jet. A couple of supercell structures 
continue to be observed with large hail the main threat. With onset 
of nocturnal cooling, updrafts should become increasingly elevated 
with a gradual weakening trend expected during the next couple of 

.Dial.. 03/18/2018 

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


Latitude...Lon 31169751 31459650 31779565 31449514 30989541 30569655 
30769745 31169751