U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 220601 
Storm Prediction Center ac 220559 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1259 am CDT Fri Jun 22 2018 

Valid 221200z - 231200z 

..there is an enhanced risk of severe thunderstorms from eastern Colorado 
into central OK... 

..there is a slight risk of severe thunderstorms across portions of 
the lower MS valley...southeast...and mid-Atlantic... 

Scattered severe storms will be possible across parts of the 
central/Southern Plains, southeast and mid-Atlantic states today. 

..southeast into the Ohio Valley and mid-Atlantic... 
Upper low currently moving through the middle MS valley is expected 
to gradually move northeastward through the Ohio Valley while 
devolving into an open wave. A series of vorticity maxima will 
rotate around this upper low, accompanied by anomalously strong 
mid-level flow, which is expected to spread across northern portions 
of the southeast and into the mid-Atlantic. 

Thunderstorms will likely be ongoing at the beginning of the period 
as one of the lobes of vorticity moves into the lower MS valley, 
providing the impetus for convection within the moist and 
low-inhibition airmass. Despite the unfavorable timing, the airmass 
will likely be moderately unstable with temperatures in the low 80s 
and dewpoints in the mid 70s helping support MLCAPE over 2000 j/kg. 
As previously mentioned, seasonally strong flow aloft will increase 
bulk shear and the potential for more robust, longer-lived updraft 
organization. Consequently, these early storms will likely pose a 
severe threat from northern la/southern Arkansas eastward across central 
MS and Alabama. Water-loaded downbursts and hail are the primary threats. 
A tornado or two cannot be ruled out, particularly on the western 
periphery of any convective line where enhanced storm-relative 
helicity from any southwestward progressing storms could contribute 
to locally higher tornado threat. 

Vorticity maximum responsible for these early day storms will 
continue eastward, likely reaching the Piedmont around or just after 
peak heating. Attendant forcing for ascent coupled with airmass 
destabilization will likely contribute to increased thunderstorm 
coverage in this region into the evening. Farther north, more subtle 
forcing may contribute to afternoon storms in the vicinity of The 
Wedge front. While the overall bulk shear will be modest, 
easterly/southeasterly winds near the boundary could enhanced 
low-level shear while also increasing vertical vorticity along the 
boundary itself. As a result, a small area of relatively enhanced 
tornado probability exists across southeast Virginia. 

..southern/Central Plains... 
Fast-moving shortwave trough currently entering the western Great 
Basin will continue eastward, moving through the High Plains during 
the afternoon and through the plains overnight. Strong Lee 
cyclogenesis is anticipated ahead of this system across southeast Colorado 
with resulting southerly flow encouraging moisture return into the 
Central Plains/High Plains. High 50s dewpoints, possibly low 60s, 
will likely arc into southeast Colorado along the northern periphery of 
the surface low. Steep mid-level lapse rates advected ahead of the 
approaching shortwave atop this at least moderately moist low-level 
airmass will result in moderate to strong instability during the 
afternoon. Additionally, increasing mid-level flow attendant to the 
approaching shortwave trough atop easterly/southeasterly results in 
strongly sheared environment. 0-6 km bulk shear over 50 kt is 
likely. All of these factors point to the potential for 
thunderstorms capable of hail over 2 inches in diameter and wind 
gusts over 60 kt across eastern Colorado. Tornadoes are also possible, 
particularly if storms are able to remain discrete. 

Strong cold pool generation coupled with the strong forcing for 
ascent and fast-moving shortwave trough all point to likelihood for 
quick upscale growth into what could be a significant mesoscale 
convective system. Steep mid-level lapse rates downstream into OK 
coupled with a strong low-level jet also point to the potential for 
a well-organized system capable of tracking much farther east than 
would normally be expected given the increased convective 

.Mosier/Wendt.. 06/22/2018 


Mesoscale Discussion

acus11 kwns 220706 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 220706 

Mesoscale discussion 0818 
National Weather Service Storm Prediction Center Norman OK 
0206 am CDT Fri Jun 22 2018 

Areas affected...Texas and Oklahoma panhandles...extreme northeast 
New Mexico...southeast Colorado...and southwest Kansas...and far 
western Oklahoma 

Concerning...severe potential...watch possible 

Valid 220706z - 220830z 

Probability of watch issuance...40 percent 

Summary...ongoing thunderstorms are increasing in coverage across 
the Oklahoma and Texas panhandles. An isolated large hail or gusty 
thunderstorm wind will be possible through the night. Trends will be 
monitored for a possible Severe Thunderstorm Watch. 

Discussion...initial thunderstorms developed during the evening 
hours across southeast Colorado, northeast New Mexico, and the 
northwest Texas Panhandle in response to modest warm-air advection 
atop a stationary front across the area. These thunderstorms 
organized into 2 or 3 primary thunderstorm cores, with the strongest 
moving southeast across Dallam County, TX, and Cimarron County, OK. 
Large hail is likely with this thunderstorm. 

Additional thunderstorms are developing to the northeast of this 
initial band of convection, with the strongest across Hansford 
County, TX, as the persistent warm-air advection allows 
surface-based parcels to isentropically ascend to their level of 
free convection. Given the larger-scale environment across the area 
-- 1000-1500 j/kg of most-unstable cape and 40-60 knots of effective 
deep-layer shear -- updraft organization is possible for any 
persistent updraft. Given the elevated nature of the thunderstorms, 
large hail should be the primary threat, although brief, gusty 
thunderstorm outflow cannot be ruled out. These thunderstorms are 
expected to continue to develop/persist through the morning hours as 
they move east, before weakening after sunrise as the low-level jet 
veers and the warm-air advection/isentropic ascent weakens. 

Trends will continue to be monitored for possible severe 
thunderstorm issuance. 

.Marsh/guyer.. 06/22/2018 

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


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