U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 251935 
Storm Prediction Center ac 251934 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0234 PM CDT Wed Apr 25 2018 

Valid 252000z - 261200z 

..there is a marginal risk of severe thunderstorms for the 
Lower/Middle Rio Grande Valley... 

Isolated strong/severe thunderstorms may affect primarily the 
Lower/Middle Rio Grande Valley region of south Texas. 


No appreciable changes are warranted to 1630z outlook. 

Strong surface heating is confined to regions west of the Rio Grande 
River and this has contributed to an axis of MLCAPE upwards of 2000 
j/kg in the Lee of the Sierra Madre orientals. Strong convection is 
evolving over the higher terrain and will soon spread toward lower 
elevations. However, it appears the strongest activity should 
struggle to spread east of the international border. For these 
reasons will maintain 5% severe probs for the U.S. Side of the 
Lower/Middle Rio Grande Valley. 

.Darrow.. 04/25/2018 

Previous discussion... /issued 1052 am CDT Wed Apr 25 2018/ 

A strong cold front is surging southward across The Big Bend region 
of TX, and is spreading eastward through The Hill Country. 
Scattered elevated thunderstorms are occurring immediately behind 
the front, with the potential for hail in the stronger cells 
throughout the day. The air mass ahead of the front continues to 
moisten and destabilize, with afternoon MLCAPE values expected to be 
around 2000 j/kg. It appears likely that a few severe thunderstorms 
will affect parts of northern Mexico, with some severe threat 
extending northward into the Rio Grande Valley of Texas. At this time, 
12z guidance and trends in observational data continue to support 
that the overall risk in central/south Texas is marginal, but an 
isolated storm or two could produce large hail and/or damaging winds 
this afternoon and evening. 


Mesoscale Discussion

acus11 kwns 242155 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 242155 

Mesoscale discussion 0288 
National Weather Service Storm Prediction Center Norman OK 
0455 PM CDT Tue Apr 24 2018 

Areas affected...portions of West Texas 

Concerning...severe potential...watch unlikely 

Valid 242155z - 250030z 

Probability of watch issuance...20 percent 

Summary...an isolated damaging wind and hail threat should develop 
eastward this evening. Watch issuance is unlikely mainly due to the 
marginal thermodynamic environment. 

Discussion...isolated thunderstorms have formed this afternoon along 
and just ahead of a surface trough located over West Texas. Surface 
temperatures have warmed into the upper 80s and lower 90s across 
this region, but low-level moisture return has been very limited 
thus far. Large temperature-dewpoint spreads generally around 40-45 
degrees imply a very well-mixed boundary layer, and convective 
downdraft winds will likely be enhanced as they reach the surface, 
possibly producing isolated severe-caliber gusts. Although winds in 
the 0-3 km layer remain weak per 2136z vwp from klbb, they do veer 
and strengthen slightly into mid-levels. This is supporting 
effective bulk shear values around 30-35 kt, which should be 
marginally supportive of organized updrafts and perhaps some hail 
threat with the strongest cores. Tendency with time should be for 
convection to congeal into some form a loosely organized 
line/cluster as it moves eastward this evening, with strong to 
locally damaging winds becoming the primary threat. The limited 
low-level moisture and resultant marginal thermodynamic environment 
should tend to keep the overall severe threat isolated, and watch 
issuance appears unlikely at this time. 

.Gleason/Thompson.. 04/24/2018 

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


Latitude...Lon 31650029 31550090 31590160 31920225 32170221 32530197 
33040206 33190209 33520190 33760093 33749993 33379952 
32869938 32389950 31989981 31650029