Severe Storm Outlook Narrative (AC)
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931
ACUS11 KWNS 042334
SWOMCD
SPC MCD 042334
ARZ000-OKZ000-050100-

Mesoscale Discussion 1781
NWS Storm Prediction Center Norman OK
0534 PM CST Mon Dec 04 2017

Areas affected...Portions of eastern OK and western/central AR

Concerning...Severe Thunderstorm Watch 519...

Valid 042334Z - 050100Z

The severe weather threat for Severe Thunderstorm Watch 519
continues.

SUMMARY...An isolated threat for mainly strong to damaging winds
should continue across WW 519 for the next several hours. Downstream
watch issuance into more of western/central AR will probably not be
needed.

DISCUSSION...Mosaic radar imagery from 2330Z depicts a broken line
of thunderstorms extending along and just ahead of a surface cold
front across eastern OK into far northwestern AR. Several other
thunderstorms have recently developed across southwestern AR within
the open warm sector. A few cells within the broken line have
exhibited supercell characteristics over the past several hours,
with sporadic large hail and strong/damaging winds being reported.
The airmass immediately downstream of this ongoing convection should
remain favorable for maintenance of severe thunderstorms in the
short term, as MLCAPE around 500 J/kg and effective bulk shear
values of 40-50 kt are present across western AR. A tornado cannot
be completely ruled out given veering low-level winds supporting
effective SRH around 275-325 m2/s2. However, the primary severe
threat will likely transition to strong/damaging winds as the
surface cold front overtakes ongoing convection, with these
thunderstorms quickly growing upscale into a southeastward-moving
squall line.

While some severe threat may exist to the east of WW 519, cooler
surface temperatures and less low-level moisture is present with
eastward extent across central AR. Resultant instability likewise
wanes into central AR. Coupled with the loss of diurnal heating
which should further reduce already weak instability, the small
spatial severe threat to the east of WW 519 may become too marginal
over the next several hours to justify a new WW in central AR.

..Gleason.. 12/04/2017

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

ATTN...WFO...LZK...SHV...TSA...OUN...

LAT...LON   34869577 35509514 36459470 36459248 35419248 33959344
            33619418 34029517 33979592 34489610 34869577




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