U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 231954 
Storm Prediction Center ac 231953 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0253 PM CDT Sat Jun 23 2018 

Valid 232000z - 241200z 

..there is a slight risk of severe thunderstorms from the Southern 
Plains to the Tennessee Valley...across the middle Atlantic and the Central 
High plains... 

Scattered severe thunderstorms are expected this afternoon and 
evening from the Southern Plains to the lower Mississippi Valley and 
a portion of the southeast states. Other severe storms are expected 
over the middle Atlantic region and Central High plains. 

Overall minor changes have been made to the day 1 outlook this 
update. Some trimming was done on the southern end of the slight 
risk from Texas to Alabama based on latest surface observation and hi-res 
guidance trends. The sig hail area was expanded north and east 
across central OK to account for the current position of the outflow 
boundary and expected storm initiation over the next couple of 
hours. See mesoscale discussion 838 for more details on this threat. 

Additional adjustments include expanding the eastern Colorado slight risk 
eastward into portions of far western Kansas as guidance has been 
consistent in maintaining storm cluster across this area this 
evening. Damaging winds and hail will be the main threats with this 
activity. See mesoscale discussion 839 for more details. 

Finally, operational hrrr guidance suggests this cluster may persist 
overnight into parts of southwest Kansas and northwest OK and a marginal 
wind and hail threat could accompany this activity. The marginal 
risk area was expanded to account for this potential. Otherwise, no 
other changes were made. 

.Leitman.. 06/23/2018 

Previous discussion... /issued 1147 am CDT Sat Jun 23 2018/ 

..TN and lower MS valley region today... 
The remnants of an overnight MCS, now moving into northwest Alabama and 
southern middle TN, will be accompanied by some threat for damaging 
winds about as far east as southeast Tennessee and northwest Georgia through 
early afternoon, given a belt of 40+ kt flow near 700 mb (enhanced 
some by the mesoscale convective vortex with the convection). However, the widespread 
clouds/convection ongoing farther to the south in Alabama casts doubt of 
the degree of destabilization possible in advance of these storms. 
Otherwise, additional strong/isolated severe storms could evolve 
from the ongoing central Alabama storms into GA, or develop this 
afternoon along the residual outflow from southeast Arkansas into MS and 
eventually spread into central Alabama (along the southern fringe of the 
current storms). Damaging outflow gusts will be the main threat. 

..northwest Texas into southern OK this afternoon into early 
the outflow boundary from overnight and ongoing convection has 
consolidated immediately north of I-20 across north central and 
northeast TX, and the boundary may begin to retreat a little to the 
north across northwest Texas this afternoon. An influx of low-mid 70s 
boundary-layer dewpoints into the boundary, along with daytime 
heating and midlevel lapse rates near 9 c/km, will boost MLCAPE into 
the 3000-4000 j/kg range this afternoon. This corridor will lie 
along the southern fringe of the stronger midlevel flow (near or 
above 30 kt), with some enhancement to low-level shear along the 
boundary. The net result will be profiles sufficient for supercells 
where deep mixing reduces convective inhibition across northwest TX, 
and in the warm advection zone to the north into southern OK this 
afternoon/evening. The strongest storms could produce isolated very 
large hail and damaging gusts. 

..Chesapeake region this afternoon/evening... 
A midlevel trough over the upper Ohio Valley will progress 
east-northeastward to southern New England tonight. Embedded speed 
maxima will continue to rotate around the southeast periphery of the 
trough and interact with a diffuse Lee trough across Virginia. The Richer 
low-level moisture/buoyancy should remain near Chesapeake Bay 
through the afternoon, while mid-upper flow/shear will be sufficient 
for organized storms. A few supercells will be possible, with a 
primary threat for a few damaging gusts. 

..Central High plains this afternoon through early tonight... 
Another midlevel trough is beginning to amplify and will move from 
the northern rockies to Wyoming/Colorado tonight. Low-level moisture is 
returning northward across southeast Colorado in the wake of overnight 
convection, and profiles will become sufficient for supercells by 
this afternoon. A few storms should form along the Palmer Divide, 
and potentially the Raton Mesa, and then spread east-southeastward 
over the plains this evening. There are still some concerns 
regarding storm coverage, but any supercells that form will be 
capable of producing large hail and damaging winds, and storms could 
grow into a small cluster and persist into early tonight. 


Mesoscale Discussion

acus11 kwns 231937 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 231936 

Mesoscale discussion 0839 
National Weather Service Storm Prediction Center Norman OK 
0236 PM CDT Sat Jun 23 2018 

Areas affected...portions of the southern/Central High plains 

Concerning...severe potential...watch possible 

Valid 231936z - 232130z 

Probability of watch issuance...60 percent 

Summary...isolated thunderstorms could pose a risk for large hail 
and damaging winds into this evening. Watch issuance could be 

Discussion...a few strong/severe storms have developed near the 
Palmer Divide eastward into northwest Kansas this afternoon, amidst 
an environment characterized by favorable effective shear, but 
modest boundary-layer moisture (e.G., Upper 40s/lower 50s dew 
points). Still, sufficient mixed-layer buoyancy exists for isolated 
multicells/splitting supercells, capable of large hail and damaging 
winds. If a few cells continue to organize and evolve southeastward 
into improved storm-relative flow and higher dew points, an 
increasing severe threat would likely evolve, perhaps in the form of 
a small convective complex. As such, convective trends are being 
monitored for possible watch issuance. 

.Picca/Thompson.. 06/23/2018 

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


Latitude...Lon 37380089 36610234 36490345 36810384 37220401 37960403 
38610412 39390414 39510396 39630343 39660210 39520114 
39030067 38040046 37380089