Severe Storm Outlook Narrative (AC)
Issued by NWS
ACUS11 KWNS 210845
SPC MCD 210844
Mesoscale Discussion 0533
NWS Storm Prediction Center Norman OK
0344 AM CDT Fri Apr 21 2017
Areas affected...Portions of the OK/TX Panhandles into western and
Concerning...Severe Thunderstorm Watch 152...
Valid 210844Z - 211045Z
The severe weather threat for Severe Thunderstorm Watch 152
SUMMARY...Recent storm development is being monitored in northeast
NM into the northwest TX Panhandle, which is likely the start of the
next round of strong to severe storms forecast to spread to the
east/southeast across the OK/TX Panhandles into western and central
OK through the morning. This will likely warrant a new WW issuance
prior to the expiration of WW 152. Meanwhile, isolated strong to
severe storms will continue across west-central OK, with storms
weakening east of the I-35 corridor.
DISCUSSION...At 08Z, the strongest storms with some severe hail
threat were persisting within and just east and southeast of WW 152.
These more isolated storms should eventually weaken, as they move
east of the I-35 corridor, where instability is much less than
currently analyzed across the western half of OK and western north
TX into the TX Panhandle.
Meanwhile, trends in IR satellite imagery have indicated an increase
in convective clouds/cooling cloud tops across northeast NM into the
northwest TX and OK Panhandles, where there has also been a recent
uptick in reflectivity per mosaic radar imagery and CAPPI data.
This activity indicated the increase in large-scale ascent spreading
into the southern Plains this morning with the approach of a
central/southern Rockies shortwave trough and accompanying
southeastward-digging mid-upper level jets. Attendant height falls
have resulted in veering and strengthening 850-mb winds across much
of west TX (from AMA southward) allowing for low-level moistening.
These factors combined with very steep midlevel lapse rates across
much of the TX/OK Panhandles into western OK has resulted in ongoing
strong destabilization during the overnight hours with MUCAPE
ranging from 1500-2000 J/kg as of 08Z.
The recent uptick in reflectivity across northeast NM and part of
the northern TX Panhandle has been depicted by the last several runs
of the HRRR, with each run suggesting a further increase in storm
development toward the east and somewhat to the southeast through
this morning. HRRR further suggests an eventual upscale growth into
a linear MCS as storms spread into western OK between 13-15Z,
reaching the I-35 corridor by late morning. Large hail will be the
initial severe-weather risk followed by a combination of damaging
winds and hail as the storms become more linear.
...Please see www.spc.noaa.gov for graphic product...
LAT...LON 35860234 36380114 36429984 36279740 36119679 35439663
34229666 34139713 34009789 34269891 34509980 34610112
34590148 35140199 35860234