U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 200522 
Storm Prediction Center ac 200520 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1220 am CDT Fri Apr 20 2018 

Valid 201200z - 211200z 

..there is a marginal risk of severe thunderstorms over a portion 
of the southern High Plains... 

A few strong to severe thunderstorms with a threat for hail and 
downburst winds are possible over the southern High Plains, mainly 
later this afternoon into early evening. 

..southern High Plains... 

Upper low now approaching The Four Corners region will move through 
the southwest states today, the southern High Plains this evening 
and the Southern Plains tonight accompanied by a Pacific cold front. 
Farther east, a large area of Continental-polar high pressure will 
advance through the eastern states, maintaining offshore flow over 
most of the Gulf Coast during the day. As a result Richer low-level 
moisture will remain south of a quasi-stationary front located over 
the northern Gulf into deep south Texas. However, the establishment 
of a southerly low-level jet will transport dewpoints in the 40s f 
through the High Plains beneath steeper mid-level lapse rates 
resulting in a corridor of marginal instability with 400-800 j/kg 
MLCAPE. Elevated thunderstorms are likely later this morning over 
northeast nm into the southern and Central High plains as forcing 
for ascent now evident on water vapor imagery over northern nm 
intercepts evolving corridor of moist advection and destabilization. 
Upstream of the morning storms, deeper mixing over the High Plains 
of New Mexico along with frontal convergence should contribute to 
thunderstorm initiation across eastern New Mexico as the boundary 
layer destabilizes during the afternoon. Forcing for ascent 
attending the upper trough will be weaker with southward extent, but 
at least isolated storms may develop over the mountains of southwest 
Texas. Vertical wind profiles accompanying the upper trough with strong 
effective bulk shear and large low-level hodographs will be more 
than adequate for organized storms including some supercell 
structures capable of mainly a few instances of large hail and 
downburst winds. However, the primary limiting factor for a more 
robust severe threat is expected to be limited moisture return and 
resulting instability. Will therefore maintain a marginal risk this 

.Dial/Gleason.. 04/20/2018 


Mesoscale Discussion

acus11 kwns 200027 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 200027 

Mesoscale discussion 0278 
National Weather Service Storm Prediction Center Norman OK 
0727 PM CDT Thu Apr 19 2018 

Areas affected...portions of southern nm into far West Texas 

Concerning...severe potential...watch unlikely 

Valid 200027z - 200300z 

Probability of watch issuance...5 percent 

Summary...a very isolated hail/wind risk may exist through this 
evening. Watch issuance is not expected. 

Discussion...low-level moisture remains limited early this evening 
across southern nm into far west TX, with surface dewpoints no 
greater than mid to upper 30s. The 00z sounding from El Paso, Texas 
shows a very deeply mixed boundary layer with MUCAPE around 650 
j/kg. A veering and strengthening wind profile through mid-levels 
and related effective bulk shear around 45-50 kt will support 
updraft organization with any thunderstorms that form/move into 
southern nm and far West Texas. At this time, thunderstorm coverage is 
expected to remain isolated at best, with the best chance for 
convection forming across the higher terrain of northern Mexico and 
moving just across the international border over the next several 
hours. Given the deeply mixed boundary layer, strong/gusty downdraft 
winds will be possible, along with some hail. Watch issuance is not 
expected due to the overall isolated nature of the severe risk. 

.Gleason/Thompson.. 04/20/2018 

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


Latitude...Lon 31640651 32140685 32470695 32680683 32730656 32430600 
31540529 31100500 30700495 30570513 30710536 31120584