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 230602 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 230601 

Mesoscale discussion 0833 
National Weather Service Storm Prediction Center Norman OK 
0101 am CDT Sat Jun 23 2018 

Areas affected...north-central and northeast Texas 

Concerning...Severe Thunderstorm Watch 201...202...203... 

Valid 230601z - 230700z 

The severe weather threat for Severe Thunderstorm Watch 201, 202, 
203 continues. 

Summary...long-lived thunderstorm cluster continues to move 
southeast across central Oklahoma. On its current trajectory, this 
cluster will move into portions of north-central and northeast Texas 
later this morning. Trends will be monitored for a potential Severe 
Thunderstorm Watch. 

Discussion...long-lived quasi-linear convective system (qlcs), with 
history of severe winds or wind damage, continues to track southeast 
across central Oklahoma. On its current trajectory, this cluster 
will begin to impact areas to the south of Severe Thunderstorm Watch 
202 and southwest of Severe Thunderstorm Watch 203 in the next 1-2 
hours. Additionally, if this trend/trajectory continues, much of 
Severe Thunderstorm Watch 203 may need to be canceled early as the 
main severe threat will remain to the southwest. 

The airmass across northeast Texas is characterized by most-unstable 
cape values in excess of 3000 j/kg and deep-layer shear of 35-50 
knots. However, as you move south of severe thunderstorm watches 202 
and 203, convective inhibition increases as well. Thinking is that 
the qlcs should be maintained for at least another few hours as it 
moves into the region, although confidence on maintaining severe 
level intensity is less certain. As such, trends will be monitored 
for the need of a small Severe Thunderstorm Watch. 

.Marsh/guyer.. 06/23/2018 

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


Latitude...Lon 33609404 33839575 33989694 34309853 34519913 34779953 
35169960 35539916 36349779 36869709 36719613 35539407 
35029317 34489311 33779345 33609404