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000
ACUS11 KWNS 271905
SWOMCD
SPC MCD 271904
OKZ000-272030-

Mesoscale Discussion 0866
NWS Storm Prediction Center Norman OK
0204 PM CDT Sat May 27 2017

Areas affected...Northern and eastern Oklahoma

Concerning...Severe potential...Watch likely

Valid 271904Z - 272030Z

Probability of Watch Issuance...95 percent

SUMMARY...A tornado watch probably will be issued by 20-21Z.  Rapid
supercell development appears likely by around 23-00Z, if not
before, particularly near the Tulsa area.

DISCUSSION...The latest objective mesoanalysis suggests that
inhibition for boundary layer parcels is at least beginning to
weaken in response to insolation along the surface frontal zone now
extending across northern Oklahoma.  More substantive weakening of
inhibition appears likely to await the southward suppression of
mid-level heights and the northern periphery of the plume of very
warm elevated mixed layer air, as coupled impulses within the
mid-latitude and subtropical westerlies continue to emerge from the
southern Rockies.  The latest Rapid Refresh, among other model
output, suggests that this may not occur until closer to, or perhaps
after, 23-00Z.  However, convective initiation seems at least
possible earlier.

Regardless, once the cap weakens, thunderstorm development will be
rapid, in the presence of strong to extreme CAPE (in excess of 4000
J/kg) and strong deep layer shear.  This probably will at least
initially include the risk for supercells, with potential for very
large hail and a couple of tornadoes, particularly on the nose of
the corridor of strongest pre-frontal surface heating, roughly in
the vicinity of Tulsa.  Additional, isolated supercell development
may not be out of the question, farther southwest along the
Interstate 44 corridor near the Oklahoma City area.

..Kerr.. 05/27/2017

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

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

LAT...LON   35699769 35919864 36339876 36749764 36979633 36899493
            36309478 35849493 35099573 34989694 35509718 35699769



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