U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 201240 
Storm Prediction Center ac 201239 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0739 am CDT sun Apr 20 2014 

Valid 201300z - 211200z 

..there is a slight risk of severe thunderstorms portions western/northwestern Texas and southwestern 

Scattered thunderstorms may drop severe hail and damaging gusts from 
the Texas South Plains across The Caprock area to northwest Texas 
and perhaps southwestern Oklahoma...mainly late afternoon into early 

Nearly zonal middle-upper-level flow courses over northern tier of 
states...perturbed primarily by shortwave trough now moving eastward from 
northern rockies. This feature will move eastward along Canadian border and 
reach northern Minnesota by end of period. Split flow will persist around two 
progressive southern-stream troughs. First of these contains embedded 
middle-upper-level low now offshore Carolinas...and forecast to move slowly 
east-northeastward over Atlantic waters through remainder period. Upstream shortwave 
ridging will shift eastward over Lower-Middle MS valley today...reaching 
central/southern Appalachians by end of period. Gradually deamplifying 
perturbation -- formerly containing closed 500-mb low -- is evident 
in moisture channel imagery from southern Colorado south-southwestward across nm and northwestern 
mex. 500-mb trough should continue slow weakening trend...while 
advancing east-northeastward to near hlc-cds-6r6 axis by 00z and top-okc-erv axis 
by 12z. 

At surface...weak low now evident over southeastern Colorado is part of Lee troughing 
regime extending from Montana to SW Texas. This low should move slowly southeastward 
to OK Panhandle or northern Texas Panhandle by 00z...with weak cold front 
southwestward over northestern nm...trough south-southwestward across Permian Basin...and dryline 
becoming better defined in vicinity of Lee trough. By 12z...low should reach 
southwestern OK...weak front to southeastern nm...dryline/trough southwestward over southeastern 
corner of nm. Initially separate frontal zone associated with 
northern-stream trough...and extending from upper MS valley southwestward over 
Nebraska...also may encourage thunderstorm development this afternoon and evening. 
However...vertical shear appears too weak for organized severe threat. 

..W Texas to southwestern OK... 
Scattered thunderstorms should develop this afternoon in vicinity of Lee 
trough/dryline...as well as over Texas Panhandle on either side of surface 
trough. This should occur after several hours of diabatic 
destabilization that weakens cinh...in wake of cloud/precipitation plume 
now extending from portions central/northern OK to west-central Texas. 
Vertical juxtaposition of slight low-level moistening with cooling 
temperatures aloft and surface heating should contribute to plume of 1000-1500 
j/kg MLCAPE ahead of dryline between 21-00z. 

Timing of middle-upper trough will put it essentially atop dryline by 
00z...by which time 500-mb flow at or above 35 knots and 250-mb winds at or above 50 knots 
should be southeast of okc-maf line and shifting eastward in step with trough 
translation. Weaker winds aloft in vicinity of middle-upper trough will greatly 
limit vertical shear and restrict potential for more than transient 
supercellular characteristics...mostly with northward extent from US-380 
corridor in northwest Texas. Capping will be more of a limiting factor with 
southward extent from there. Midlevel lapse rates will be steepest near 
trough aloft...where coldest 300-600 mb layer air should pass. As 
such...best overlap of at least marginally favorable parameters appears 
most probable inside 15% wind/hail and categorical slight line. 
Though some convection should persist well into overnight hours over 
parts of North Texas and/or southern OK...severe threat should wane with eastward extent 
into stabilizing boundary layer. 

.Edwards/Rogers.. 04/20/2014 

Mesoscale Discussion

acus11 kwns 200000 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 200000 

Mesoscale discussion 0372 
National Weather Service Storm Prediction Center Norman OK 
0700 PM CDT Sat Apr 19 2014 

Areas affected...trans-Pecos...Pecos Valley of West Texas 

Concerning...severe potential...watch unlikely 

Valid 200000z - 200130z 

Probability of watch issuance...20 percent 

Summary...localized mesoscale convective vortex with embedded supercells will pose a 
near-term risk for large hail and severe wind gusts. This activity 
should diminish after sunset amidst progressively weaker instability 
with eastern extent. 

Discussion...an mesoscale convective vortex centered over southern Reeves County with embedded 
supercells arcing into northestern Presidio County have had a history of 
radar-algorithm derived large hail along with storm-relative inbound 
velocities up to around 90 knots. Although downstream surface dew 
points have mixed into the middle 40s at kfst...these probable severe 
storms should move across this area within the hour. 

Latest objective analysis suggests minimal MLCAPE exists east of the 
Pecos River. Even so...steep tropospheric lapse rates and already 
established storm-scale organization suggest at least a marginal 
severe risk may extend to a couple of hours after sunset...before 
nocturnal cooling/stabilization finally yield dissipation of 
rotating updrafts. 

.Grams/Mead.. 04/20/2014 

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


Latitude...Lon 31210373 31310367 31620261 31570203 31080131 30290112 
29710137 29010310 29090338 30090406 31210373