Severe Storm Outlook Narrative (AC)
Issued by NWS
ACUS11 KWNS 260331
SPC MCD 260330
Mesoscale Discussion 0555
NWS Storm Prediction Center Norman OK
1030 PM CDT Tue Apr 25 2017
Areas affected...Portions of central/eastern Oklahoma
Concerning...Severe Thunderstorm Watch 159...
Valid 260330Z - 260500Z
The severe weather threat for Severe Thunderstorm Watch 159
SUMMARY...Primary severe threat has likely transitioned to
occasional instances of large hail, with the greatest threat focused
over southern/eastern portions of Watch 159.
DISCUSSION...Convection has blossomed across much of central
Oklahoma this evening, probably in response to a strengthening
south/southwesterly low-level jet. While these storms are likely
rooted above the surface, residual steep mid-level lapse rates and
strong deep-layer shear will support a continued threat for large
hail over the next few hours. Additionally, a few cells may merge
into small bowing segments, with perhaps enough downward momentum to
penetrate a weakly stable surface layer, potentially resulting in
isolated instances of strong/damaging winds.
Farther southeast, somewhat more discrete convection has evolved,
with a supercell over southern Seminole Co, OK as of 0320 UTC.
Despite surface dew points in the mid 60s, mean mixing ratios of
only 10-12 g/kg and dry mid-levels are likely precluding a greater
tornado threat. Indeed, the radar evolution of these cells has been
relatively consistent with a dry environment (e.g., higher ZDR in
the hook suggesting a lack of smaller drops due to considerable
evaporation in the RFD). Nonetheless, a threat for a brief/weak
tornado may persist, and Watch 159 may be expanded eastward across
parts of the Tulsa CWA.
...Please see www.spc.noaa.gov for graphic product...
LAT...LON 34879791 36359662 36849601 36839507 36359471 36279470
35069534 34639648 34679743 34879791