U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 171957 
Storm Prediction Center ac 171956 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0256 PM CDT Sat Mar 17 2018 

Valid 172000z - 181200z 

..there is a slight risk of severe thunderstorms across parts of 
Texas...northwest Louisiana and far southwest Arkansas... 

..there is a slight risk of severe thunderstorms across parts of 
the southern Appalachians into northern and eastern North 

..there is a marginal risk of severe thunderstorms across parts of 
the Southern Plains and arklatex... 

..there is a marginal risk of severe thunderstorms across parts of 
the Ohio and Tennessee valleys eastward into virgina and North 

Severe thunderstorms with wind damage and hail are expected this 
afternoon into tonight from the southern Appalachians eastward into 
parts of northern and eastern North Carolina. Severe thunderstorms 
with large hail and wind damage will also be possible across parts 
of central and northeast Texas into the arklatex. 

Only two changes have been made to the outlook for this issuance. 
The first change is to expand the slight risk area in central Texas 
westward to the western edge of the ongoing convection. This change 
includes a westward expansion of the wind damage, hail and tornado 
probabilities. The second change to the outlook is to expand the 
marginal risk in the southern Appalachians southward into far 
northeast Alabama and far northern Georgia. The hrrr is suggesting 
that convection will initiate in eastern Kentucky and middle 
Tennessee. If this occurs, a marginal severe threat may affect areas 
a bit further south. 

.Broyles.. 03/17/2018 

Previous discussion... /issued 1132 am CDT Sat Mar 17 2018/ 

..Central/Northeast Texas to The Ark-la-tex... 
Coincident with the leading edge of stronger cyclonic flow aloft, 
12z upper-air analysis sampled a mid-level cold pocket over the 
southern High Plains with a strong southern stream/sub-tropical jet 
extending from northern Mexico eastward into central/North Texas. At 
midday, low-level stratus continues to stream northward across 
south-central/East Texas coincident with increasingly prevalent 
middle/upper 60s f surface dewpoints. 

By mid/late afternoon, as clouds thin, concern exists for the 
possibility of initial surface-based storm development across the 
north-central Texas Big Country near a triple point characterized by 
a gradually deepening surface wave near a stationary front/dryline 
intersection. Some supercells can be expected in the presence of 
long hodographs influenced by strengthening mid/high-level 
westerlies. Moderate buoyancy, relatively steep lapse rates and the 
long/relatively straight hodographs should support some splitting 
supercells with large hail as the primary hazard. While low-level 
winds and related vertical shear/srh will not be strong initially, 
some low-level strengthening will occur by early evening and there 
will be a risk for a couple of tornadoes. 

..south-central Appalachians/North Carolina... 
A mid-level shortwave trough moving toward northern/central Illinois 
at midday will gradually accelerate southeastward today and interact 
with an increasingly moist environment across the region along/south 
of an advancing warm front. Initial strong to severe thunderstorm 
development is likely to occur across east/southeast Kentucky this 
afternoon. Aided by steep mid-level lapse rates and strong 
deep-layer shear, this includes the possibility of supercells 
capable of large hail, with damaging winds also a concern. Storms 
should continue to increase and progress east/southeastward this 
evening into far southern Virginia and North Carolina potentially as 
a semi-organized mesoscale convective system. 


Mesoscale Discussion

acus11 kwns 172306 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 172306 

Mesoscale discussion 0131 
National Weather Service Storm Prediction Center Norman OK 
0606 PM CDT Sat Mar 17 2018 

Areas affected...portions of eastern KY/TN...far southern 
WV...southwestern Virginia...and far western NC 

Concerning...Severe Thunderstorm Watch 10... 

Valid 172306z - 180100z 

The severe weather threat for Severe Thunderstorm Watch 10 

Summary...isolated marginally severe hail and strong/gusty winds may 
continue for the next several hours across remaining valid portions 
of Severe Thunderstorm Watch 10. 

Discussion...fast mid-level westerly flow of 50-70+ kt is present 
across eastern Kentucky/Tennessee and vicinity in associated with a shortwave 
trough over the Ohio Valley. Thunderstorms have formed generally along 
and south of a front oriented generally west-to-east across this 
region over the past several hours. The strong mid-level flow is 
promoting effective bulk shear of 35-50 kt, which is more than 
sufficient to organize updrafts. But, the very limited low-level 
moisture present across this region has generally tempered overall 
thunderstorm strength/severity thus far. Still, marginally severe 
hail and strong to perhaps locally damaging winds will remain 
possible across valid portions of ww 10 for the next several hours. 
The best, albeit isolated, severe potential may exist across 
southern portions of the ww (eastern tn) where surface dewpoints are 
slightly higher than farther north. The loss of daytime heating by 
late this evening will further reduce the already limited 
instability, and interaction with the mountainous terrain of eastern 
Tennessee/southwestern Virginia/far western NC will likely result in weakening of 
convection with eastward extent. 

.Gleason.. 03/17/2018 

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


Latitude...Lon 36688493 37858314 37428134 36598141 35798224 35598406 
35838487 36688493