U.S. Severe Weather Forecast (Konvektīvā prognoze)

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 232214 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 232214 

Mesoscale discussion 0844 
National Weather Service Storm Prediction Center Norman OK 
0514 PM CDT Sat Jun 23 2018 

Areas affected...central/eastern Wyoming...western Nebraska...and 
southwestern South Dakota 

Concerning...severe potential...watch unlikely 

Valid 232214z - 232315z 

Probability of watch issuance...5 percent 

Summary...scattered storms continue to migrate eastward across the 
discussion area and will pose a threat for occasional, isolated hail 
and damaging wind gusts through sunset. A ww issuance is not 

Discussion...scattered strong to occasionally severe thunderstorms 
continue to migrate/propagate eastward across Wyoming this 
afternoon. These storms are in a weakly unstable environment 
(500-1000 j/kg sbcape), with 30-45 kt deep shear profiles and steep 
low- to mid-level lapse rates supporting occasional, yet isolated 
severe hail and wind in the most intense cells. Large-scale lift 
associated with an upstream wave over the northern rockies is also 
enhancing storm coverage and should continue to do so through the 
evening before low-level stabilization lowers the overall severe 
threat. Some upscale growth into linear segments may occur in 
southeastern Wyoming and western Nebraska overnight, resulting in a 
lingering severe threat in these areas. The overall magnitude of 
the threat should preclude any ww issuance, however. 

.Cook/grams.. 06/23/2018 

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


Latitude...Lon 43700892 44040809 44120667 44100450 43870300 43450227 
42560189 41690208 41290291 41440449 41500525 41570652 
41600766 41910864 42600912 43120916 43700892