U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 230606 
Storm Prediction Center ac 230605 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0105 am CDT Sat Jun 23 2018 

Valid 231200z - 241200z 

..there is a slight risk of severe thunderstorms from the Southern 
Plains through the southeast states and over the middle Atlantic 

Scattered severe storms are expected from the Southern Plains to 
lower Mississippi Valley and a portion of the southeast states. 
Other severe storms are expected over the middle Atlantic region. 
More isolated strong to severe storms might occur over a portion of 
the central and northern plains. 

..Southern Plains... 

Outflow boundary from ongoing mesoscale convective system will reinforce stationary front 
currently situated near the OK/Texas border. This boundary might shift 
a little farther north into OK today. Diabatic heating of the moist 
warm sector will contribute to strong instability in the vicinity of 
and south of the front (2000-3000 j/kg mlcape), but a capping 
inversion should limit thunderstorm initiation much of today. 
Current thinking is that storms may initiate by late afternoon near 
the intersection of the dryline and front across northwest Texas. 
Additional storms may also develop farther east within frontal zone, 
especially during the evening as the southerly low-level jet 
strengthens. A belt of modest winds aloft with 25-30 kt at 500 mb 
will result in 35-40 kt effective bulk shear near/north of the front 
where surface winds will remain backed to easterly. Weaker shear 
will reside in warm sector. Both multicell and some supercell 
structures will be possible with damaging wind and large hail the 
main threat from late afternoon into the evening. Higher severe 
probabilities may be needed in later updates, but uncertainty 
imposed by ongoing mesoscale convective system regarding where the corridor of greater 
severe potential will be located precludes an upgrade at this time. 

..lower Mississippi Valley through southeast states.... 

Mesoscale convective system may still be in progress over the lower MS valley region and 
most likely over Arkansas. It remains uncertain whether this activity will 
be severe, but remnant mesoscale convective vortex and outflow boundaries accompanying the 
mesoscale convective system will provide a focus for additional development during the day. 
The downstream atmosphere will likely become moderately unstable 
with up to 2500 j/kg MLCAPE. A belt of stronger winds aloft will 
accompany the mesoscale convective vortex/shortwave trough, and storms will likely 
reintensify during the afternoon. The environment appears supportive 
of swaths of damaging wind through the afternoon into the early 

..middle Atlantic region... 

Warm front will lift north through Virginia and into PA during the day 
ahead of a cold front accompanying a shortwave trough. Diabatic 
warming of the moist warm sector will result in moderate 
instability. A belt of stronger winds aloft will accompany the upper 
low as it shifts northeast and transitions to an open wave. Storms 
are expected to develop over the higher terrain with a Lee trough 
across central Virginia also becoming a focus for development. Storms may 
organize into broken bands as they develop east with also some 
potential for mid-level updraft rotation given effective bulk shear 
increasing to 30-40 kt. Damaging wind will be the main threat, but 
some hail will also be possible. 

..central through northern plains... 

Ascent accompanying a shortwave trough moving southeast through the 
northern rockies and diabatic heating will promote thunderstorm 
development over the higher terrain. High based storms capable of 
downburst winds and hail appears to be the main threat. 

Farther east across South Dakota into eastern NE, surface trough accompanying 
a lead shortwave trough will provide a focus for storm development 
during the afternoon. Modest winds aloft will promote multicell 
storm modes with a few instances of marginally severe hail and gusty 
winds possible. 

.Dial/Wendt.. 06/23/2018 


Mesoscale Discussion

acus11 kwns 230945 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 230945 

Mesoscale discussion 0834 
National Weather Service Storm Prediction Center Norman OK 
0445 am CDT Sat Jun 23 2018 

Areas affected...Arkansas 

Concerning...Severe Thunderstorm Watch 203... 

Valid 230945z - 231115z 

The severe weather threat for Severe Thunderstorm Watch 203 

Summary...isolated severe thunderstorms will continue through the 
morning hours. Large hail and gusty winds will be the primary 

Discussion...long-lived quasi-linear convective system 
(qlcs)/mesoscale convective system (mcs) turned eastward across 
southeast Oklahoma and continues to progress eastward through 
Arkansas. The activity appears to be moving along the north side of 
a Theta-E gradient, with the best moisture and instability to the 
south of the precipitation shield. However, sufficient instability 
and deep-layer shear across Arkansas should allow for a few more 
hours of isolated large hail and gusty thunderstorm wind potential. 
The combination of additional thunderstorm development ahead of the 
ongoing qlcs/MCS, and a cooler, more stable airmass across northern 
Mississippi, should promote an overall weakening trend. This appears 
to be underway as latest infrared satellite imagery has indicated a 
warming of cloud temperatures of late. 

A local extension of Severe Thunderstorm Watch 203 may be necessary 
for portions of east-central Arkansas, and the need for this will be 

.Marsh.. 06/23/2018 

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


Latitude...Lon 33809437 35119346 35119127 34199080 33569182 33809437