U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 241302 
Storm Prediction Center ac 241300 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0800 am CDT sun Jun 24 2018 

Valid 241300z - 251200z 

..there is an enhanced risk of severe thunderstorms across the 
south-Central High plains... 

Severe storms capable of significant damaging wind, large hail and 
possibly a few tornadoes are expected from southeast Colorado 
through southwest Kansas, the Texas and Oklahoma panhandles and 
northwest Oklahoma. Other severe thunderstorms can be expected 
across additional parts of Kansas and Nebraska as well as the 
mid-south region and Tennessee Valley. 

..eastern Colorado to south-Central Plains... 
Significant convection including an mesoscale convective system that crossed 
northern/eastern Oklahoma overnight and related outflow, as well as 
regenerative Post-mesoscale convective system convection across northwest Oklahoma/southwest 
Kansas, are considerable factors for the severe risk later today. It 
seems likely that the greatest destabilization will occur on the 
west/southwest fringes of this early-day activity, although some 
northward retreat of the outflow-reinforced boundary may occur. 
Moderate to strong destabilization appears most likely from 
southeast Colorado into the Oklahoma/Texas panhandles and western 
Oklahoma late this afternoon/early evening. 

With aid of upslope flow, current thinking is that storms will 
initially develop and intensify this afternoon along the Front Range 
vicinity of east-central/southeast Colorado, and subsequently into 
the south-Central High plains vicinity by late afternoon/early 
evening. Aided by a mid-level jet accompanying the mid-latitude 
shortwave trough and easterly low-level winds, more than sufficient 
effective bulk shear will exist for supercells. Large hail, and 
possibly a couple of tornadoes will be the initial threats. But 
storms are likely to grow upscale into an mesoscale convective system and continue generally 
eastward with damaging wind becoming the primary threat this evening 
into the overnight. 

..northern Kansas into central/eastern Nebraska and mid-Missouri 
although the influence of extensive convection to the south may be a 
detrimental factor, storms are expected to develop along a surface 
boundary where the atmosphere should become moderately unstable 
during the afternoon. Wind profiles will undergo some increase with 
the approach of the upper trough with 30-35 kt effective bulk shear 
supportive of multicells and possibly some supercell structures 
capable of damaging wind and large hail through mid-evening. 

..mid-south to Tennessee Valley... 
A well-organized and long-lived quasi-linear mesoscale convective system continues to 
persist across Arkansas early this morning, likely with aid of a 
trailing mesoscale convective vortex across far northeast Oklahoma. Various 
convection-allowing models including overnight hrrr runs have tended 
to erroneously predict a weakening of this convection. It is 
plausible that this mesoscale convective system persists and even re-intensifies within a 
moist and diurnally destabilizing boundary layer. At the very least, 
the parent mesoscale convective vortex will likely provide favorable forcing for ascent, as 
well an enhanced belt of mid-level winds/deep-layer shear, for 
severe-conducive development into the afternoon as it spreads 
eastward across the region. Damaging winds should be the most common 
concern, but severe hail and even some tornado risk may exist 
through early evening. 

..mid-Atlantic states/Carolinas... 
An east/northeastward-moving shortwave trough will influence the 
region as it moves from the Ohio Valley toward the north-central 
Appalachians, with moderate downstream destabilization expected 
near/ahead of a front and surface trough. While low-level 
convergence will not be overly strong in most areas, adequate 
instability, especially when coupled with moderate deep-layer shear 
over the mid-Atlantic region, could allow for isolated severe 
thunderstorms capable of locally damaging winds and possibly some 
hail this afternoon into early evening. 

.Guyer/marsh.. 06/24/2018 


Mesoscale Discussion

acus11 kwns 241238 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 241237 

Mesoscale discussion 0856 
National Weather Service Storm Prediction Center Norman OK 
0737 am CDT sun Jun 24 2018 

Areas affected...extreme northeast Texas...much of 
Arkansas...northwest Mississippi...and far western Tennessee 

Concerning...Severe Thunderstorm Watch 211... 

Valid 241237z - 241430z 

The severe weather threat for Severe Thunderstorm Watch 211 

Summary...thunderstorms ongoing across western Arkansas will 
continue to pose a risk for large hail and strong, gusty winds as 
they move into central Arkansas. The environment ahead of this 
thunderstorm cluster suggests that a new Severe Thunderstorm Watch 
may be needed east of the current watch. 

Discussion...long-lived mesoscale convective system (mcs) with 
leading edge Bow-echo continues across western Arkansas. Recent 
radar trends suggest an uptick in intensity as the mesoscale convective system is moving 
into central Arkansas. Surface dewpoints in the 70s and diurnal 
heating will allow for continued destabilization ahead of this 
feature. Thus, most-unstable cape values currently around 2000 j/kg 
should only increase through the morning. Additionally, this area is 
on the southern fringe of the better deep-layer shear, which will 
only act to further thunderstorm organization and mesoscale convective system maintenance. 
Thus, the severe threat may continue through the morning and begin 
to impact areas outside of Severe Thunderstorm Watch 211. The region 
will continue to be monitored for the potential of an additional 
Severe Thunderstorm Watch to the east of watch 211. 

.Marsh/guyer.. 06/24/2018 

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


Latitude...Lon 33509557 35709417 36099164 34938954 33099090 33509557