- 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
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.
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.
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.
..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