Aug 14, 2018 1300 UTC Day 1 Convective Outlook
Updated: Tue Aug 14 14:10:30 UTC 2018 (20180814 1300Z Day 1 shapefile | 20180814 1300Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20180814 1300 UTC Day 1 Outlook Graphic
Day 1 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
MARGINAL 108,496 5,766,018 Oklahoma City, OK...Tulsa, OK...Raleigh, NC...Fayetteville, NC...Cary, NC...
Probabilistic Tornado Graphic
20180814 1300 UTC Day 1 Tornado Probabilities Graphic
Probability of a tornado within 25 miles of a point.
Hatched Area: 10% or greater probability of EF2 - EF5 tornadoes within 25 miles of a point.
Day 1 Tornado Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
2 % 32,764 2,941,091 Oklahoma City, OK...Tulsa, OK...Norman, OK...Lawton, OK...Broken Arrow, OK...
Probabilistic Damaging Wind Graphic
20180814 1300 UTC Day 1 Damaging Wind Probabilities Graphic
Probability of damaging thunderstorm winds or wind gusts of 50 knots or higher within 25 miles of a point.
Hatched Area: 10% of greater probability of wind gusts 65 knots or greater within 25 miles of a point.
Day 1 Wind Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
5 % 95,824 5,746,816 Oklahoma City, OK...Tulsa, OK...Raleigh, NC...Fayetteville, NC...Cary, NC...
Probabilistic Large Hail Graphic
20180814 1300 UTC Day 1 Large Hail Probabilities Graphic
Probability of hail 1" or larger within 25 miles of a point.
Hatched Area: 10% or greater probability of hail 2" or larger within 25 miles of a point.
Day 1 Hail Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
5 % 99,348 5,325,666 Oklahoma City, OK...Tulsa, OK...Raleigh, NC...Fayetteville, NC...Cary, NC...
   SPC AC 141410

   Day 1 Convective Outlook CORR 1
   NWS Storm Prediction Center Norman OK
   0910 AM CDT Tue Aug 14 2018

   Valid 141300Z - 151200Z



   Marginally severe thunderstorms are possible this afternoon into
   evening over parts of the north-central Rockies/High Plains region,
   eastern North Carolina, as well as portions of Oklahoma and southern

   The mid/upper-level pattern over the contiguous U.S. will be rather
   disheveled through the period, with the primary belt of northern-
   stream westerlies remaining over Canada.  A broad cyclone now
   covering the central/northern Appalachians and much of the Northeast
   will move slowly northeastward while gradually weakening to an open
   wave late this period or early day 2.  Another cyclone -- currently
   covering much of the central/southern plains with a primary
   circulation center over central KS -- will move slowly east-
   northeastward through the period, also becoming an open-wave trough.
   By 12Z the trough should be near the KS/MO line and over eastern OK.
   An embedded vorticity lobe -- now apparent in moisture-channel
   imagery over the HYS/HLC area -- is forecast to dig southeastward to
   northern OK this evening then pivot eastward toward the western
   Ozarks.  A basal shortwave trough over the northern Rockies occupies
   the southwest end of a persistent/positively tilted synoptic trough
   that extends to Hudson Bay.  The shortwave trough will amplify
   steadily as it moves east-southeastward across MT, reaching the
   western Dakotas and northeastern WY by 12Z. 

   At the surface, a weak, wavy, quasistationary frontal zone was drawn
   from the coastal Mid-Atlantic across eastern/central NC, central SC,
   northern portions of GA/AL, then northwestward arching across the
   STL and OMA areas as a warm front, then southwestward to a surface
   low near SPD.  A cold front associated with the northern-stream
   synoptic trough was drawn from the James Bay region to south-central
   MN, becoming quasistationary to the central High Plains.  

   ...North-central Rockies/High Plains...
   Convection evolving from an ongoing cloud/precip shield over
   southeastern MT/northeastern WY may produce isolated severe hail
   through early afternoon as it moves east-southeastward.  Additional
   thunderstorms are expected to develop this afternoon over higher
   terrain of eastern WY and move east-southeastward to southeastward,
   offering hail as well as isolated severe gusts. 

   Convective potential will be aided by a combination of favorable
   residual moisture (surface dew points commonly 50s F), diurnal
   heating south of the morning cloud/precip area, and post-frontal
   upslope flow.  The latter will provide enhanced storm-relative
   boundary-layer winds, as well as contribute to enough veering of
   flow with height to yield 40-45-kt effective-shear magnitudes. 
   Buoyancy will be on the marginal side, with MLCAPE reaching 800-1200
   J/kg, but still sufficient to support multicells and transient
   supercells moving into a favorably well-mixed boundary layer for
   sporadic hail and strong-severe gusts.  Activity should weaken this
   evening as it moves into lower-theta-e air.

   Scattered thunderstorms are expected to develop this afternoon over
   the outlook area, offering the potential for isolated severe
   hail/gusts and a conditional, lower-end tornado risk. 

   Satellite imagery shows a broad clear slot across the region, over
   the southern semicircle of the mid/upper cyclone.  This feature is
   related to a corridor of midlevel drying analyzed on last night's
   00Z upper-air charts, and evident in available soundings this
   morning.  It should persist today, north of the southwest-northeast
   plume of profuse low/middle-level moisture, cloud cover and embedded
   convective precip that covers parts of north TX, southern/eastern OK
   and into the Ozarks.  Forecast soundings suggest that sustained
   heating of a favorably moist boundary layer in that slot will offset
   modest lapse rates aloft over central/northeastern OK, and act in
   concert with somewhat greater lapse rates over western/northern
   areas nearer the cyclone core and in a zone of DCVA aloft.  The
   result should be around 2000-3000 J/kg MLCAPE.

   Favorable buoyancy and low-level theta-e will be juxtaposed with a
   belt of somewhat enhanced middle-level flow to aid in storm
   organization.  Anvil-level flow, low-level winds and hodographs each
   are progged to remain modest on the meso-alpha scale.  However,
   localized vorticity enhancement along outflow/differential-heating
   boundaries may promote short-lived development/tightening of
   low-level rotation on the storm scale.  As such, a marginal tornado
   risk exists, as well as locally strong-severe gusts and sporadic

   ...Eastern NC...
   Isolated to widely scattered thunderstorms may develop this
   afternoon near a surface lee trough and residual frontal zone,
   across the eastern Piedmont/western coastal plain.  The most intense
   cores may yield marginally severe hail/gusts.

   The frontal zone, while losing baroclinicity, still demarcates very
   moisture-rich Atlantic marine air to the south from lower theta-e in
   VA, beneath the southern rim of somewhat enhanced mid/upper cyclonic
   flow.  Low-level flow/lift along these boundaries should be weak,
   but in concert with strong surface diabatic heating, still
   sufficient for at least a few sustained cells to develop.  By
   early/mid-afternoon, weak MLCINH and near-70 F surface dew points
   will be in place, supporting 2000-2500 J/kg MLCAPE, amidst roughly
   35 kt effective-shear magnitudes.

   ..Edwards/Peters.. 08/14/2018