U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 210055 
Storm Prediction Center ac 210054 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0754 PM CDT sun may 20 2018 

Valid 210100z - 211200z 

..there is a marginal risk of severe thunderstorms for parts of Texas 
and southern and eastern MO... 

Isolated strong to locally severe thunderstorms are possible this 
evening in portions of Texas and the middle Mississippi Valley. 

..middle MS valley... 
A band of thunderstorms associated with a weak mid-level disturbance 
will continue east-northeast across eastern MO during the evening. 
A couple of strong gusts or marginally severe hail are possible with 
the stronger cores before the gradually cooling boundary layer leads 
to a weakening of storms and a diminished severe threat. 

The southern portion of a long-lived band of convection on the 
leading edge of a composite front/outflow will push south-southeast 
across the lower coastal plain of Texas this evening. The evening 
upper-air sounding from Corpus Christi showed moderate instability 
and relatively high precipitable water but only marginal shear for 
storm organization. As a result, water-loaded downdrafts and a low 
risk for large hail may accompany the strongest storms before this 
activity moves off the coast later this evening. Farther west, a 
few storms over southwest Texas may continue to move across the Rio 
Grande and pose an isolated hail/wind threat. These storms will 
weaken during the next 1-2 hours and the severe risk will subside. 

.Smith.. 05/21/2018 


Mesoscale Discussion

acus11 kwns 202326 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 202326 

Mesoscale discussion 0479 
National Weather Service Storm Prediction Center Norman OK 
0626 PM CDT sun may 20 2018 

Areas affected...western Kentucky...western Tennessee...eastern 
Arkansas...and northern Mississippi 

Concerning...Severe Thunderstorm Watch 110... 

Valid 202326z - 210030z 

The severe weather threat for Severe Thunderstorm Watch 110 

Summary...an isolated damaging wind threat continues across 
remaining portions of ww 110, although much of the region has 
stabilized recently due to convective overturning. Portions of ww 
110 may be cancelled before the 01z expiration time. 

Discussion...storms continue to propagate slowly/erratically in and 
near the remaining valid portions of ww 110 currently. These storms 
are in a weakly sheared environment, with widespread convective 
overturning and expanding rain-cooled air/outflow limiting the 
magnitude of surface-based instability needed to maintain a robust 
severe threat. Storms propagating through the warm, moderately 
unstable pre-convective airmass (in eastern Arkansas and near middle 
tennessee) may continue to pose a threat for isolated damaging wind 
gusts in the short term, although ongoing trends suggest that the 
overall severe threat will continue to wane through 01z. Some 
portions of ww 110 may be cancelled early as a result. 

.Cook.. 05/20/2018 

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


Latitude...Lon 36129127 36169085 36289008 36498937 36948847 37438791 
37858766 37918731 37748715 37058733 36088769 35388799 
34438825 33998832 33738853 33698929 33809036 33999111 
34119139 34579138 35409127 36129127