SPC MD 555

MD 0555 CONCERNING SEVERE THUNDERSTORM WATCH 159... FOR PORTIONS OF CENTRAL/EASTERN OKLAHOMA

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
continues.

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.

..Picca.. 04/26/2017

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...TSA...OUN...

LAT...LON   34879791 36359662 36849601 36839507 36359471 36279470
            35069534 34639648 34679743 34879791 

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